no power under load + backfires - fuel pressure? ignition? sensors/ecu?

hi everyone,

i originally posted this under the 2nd gen thread, but i think that was the wrong place.

i'm working on a '91 mighty max 2.4 for a friend, and it was running super rough, hard start, etc. i did lots of things, swapped a bunch of parts with a '96 mighty max parts car, and finally swapped the entire exhaust manifold/catalytic converter. this fixed the main issues -- i think it was a combo of failed spark wire and warped manifold/busted studs leading to clogged cat. however, during the process i changed the distributor timing, and didn't have a timing light so had to set it by feel.

things were a lot better, but still having very weak power at low RPMs or on hills (under load). i suggested not to drive it much until i got a timing light, but i think it got driven at least a hundred miles. :(

got the timing light, and the timing was way advanced, i think. like 15-20 degrees (!?!). i was jumping the wrong jumper at first, so that was the post-computer timing. now, with correct jumper, the timing is a steady 7 deg BTDC. however, with jumper ungrounded, it jumps around from ~9 degrees to ~14 or so. not smooth, each rotation is a bit different. not sure if that's normal?

anyway, now it starts well and everything is a lot smoother -- but still getting pretty terrible power at low RPM under load, and also backfires. not huge ones, put pretty frequent coughs/puffs of smoke. i drove it for ~10 miles to see if the computer just needed to reset, but not much change. disconnected battery, cleaned connections, and reattached (ie. reset ECU), no apparent change.

at idle (which is more or less ok, though it wanders), when i open the throttle, the RPMs go *down* and it bogs, almost cuts out, unless i feather it. sounds to me like fuel isn't getting added when throttle opens, right?

disconnecting the TPS or the MAF sensors appears to have little or no impact on the problem. i *think* this means they're not likely culprits. i'm not hearing misfires, so that makes me think spark is less likely the problem.

so: fuel, right? what's the best way to attach a pressure tester to these trucks -- i know some folks have had a hard time with it? the only other thing that makes me doubt fuel is that the truck was running fine before the spark/exhaust manifold issues cropped up, and it would be strange if a completely unrelated thing bust as well... yeah?

other thoughts?

appreciate the help!

Does the distributor have a vacuum advance? Test the vacuum diaphragm actuator see if it holds vacuum & advances the timing? Remove air cleaner cover with engine off look down the carburetor while opening the throttle you should see gas streams from the acceletator pump (does it have a carb?)

thanks for the response!

it's a fuel injected engine, no carb. not sure if there's an analogous way to check how much fuel's coming out of the injectors.

i don't *think* there's a vacuum advance, but i'll check tomorrow. but your point makes me wonder: maybe there's a problem with the mechanical advance in the distributor? especially since the problem shows even when i revv the engine with the car in neutral -- it bogs down unless i feather it. then when i get to high rpms (like, maybe the mechanical advance unsticks??) it seems to be better.

what's the best way to test this? i do have this '96 parts car sitting here, would it make sense to swap distributors and see if that changes anything, or is there something else that would be easier?

thanks again!

Quote:

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Originally Posted by xboxrox

Does the distributor have a vacuum advance? Test the vacuum diaphragm actuator see if it holds vacuum & advances the timing? Remove air cleaner cover with engine off look down the carburetor while opening the throttle you should see gas streams from the acceletator pump (does it have a carb?)

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4G64 doesn't have a vacuum advance - all controlled by the ECU. You need to do some basic checks. First see if you are getting ANY codes from the ECU that indicate a fault. The ECU's themselves are notorious for failing but are not a nightmare to fix or diagnose. Cracking the ECU case open and a visual inspection usually reveals bad capacitors or worse case scenario bad tracks on the PCB. If the ECU has failed, it will operate in 'limp home' mode which means it'll run, but not be happy about it.

To check the mechanical (or any 'n all advancing going on) would'nt it be easiest if you used a timing light while revving the engine..? Locate & put a big blob of white on the pully timing mark so it's easy to see... I used my wife's fingernail polish pen with white color...

Actually, I don't know if my timing idea will work on a fuel injected ECU engine, I assume your motor has a distributor, maybe not..? I would just remove the dist cap and try moving the base plate parts that move when the mechanical advance is activated... Could be things are stuck or in need of cleaning & some lube... Try not removing the distributor unless that's the only way to fix it, too much work in my opinion... Sometimes we break more than we fix, I do, so it often pays to do only what's needed & no more... I have a 50/50 success rate...

Hoping for your Success
George

thanks for both responses! a few updates and replies:

first, i swapped the ECU with the '96 computer, and no changes in the symptoms. so i *think* that rules out busted caps.

second, i checked the codes and just get a neverending quick blink, which i believe means no codes. same as last time i checked, before the ECU was reset.

third, i believe that the timing does not really advance cleanly when revved, but i'm going to do it again with better lighting. so that *would* tend to imply the mechanical advance?

finally, that's a good idea about working with the baseplate parts. i took out the distributor from the parts car, but having a heck of a time getting the wiring connector phillips screws to unstick. so if i can avoid moving the distributor that's better.

any particular hints on messing with the base plate?

thanks!

Quote:

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Originally Posted by xboxrox

To check the mechanical (or any 'n all advancing going on) would'nt it be easiest if you used a timing light while revving the engine..? Locate & put a big blob of white on the pully timing mark so it's easy to see... I used my wife's fingernail polish pen with white color...

Actually, I don't know if my timing idea will work on a fuel injected ECU engine, I assume your motor has a distributor, maybe not..? I would just remove the dist cap and try moving the base plate parts that move when the mechanical advance is activated... Could be things are stuck or in need of cleaning & some lube... Try not removing the distributor unless that's the only way to fix it, too much work in my opinion... Sometimes we break more than we fix, I do, so it often pays to do only what's needed & no more... I have a 50/50 success rate...

Hoping for your Success
George

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I used a driver drill with the best fitting + driver tip I could find to remove carburetor screws that my bare hands could'nt budge... Start with low setting then keep increasing until the screws finally come loose.
You'll get it:thumbup:

Get a JIS* screwdriver or bit set. Hozan or Vessel brands are good and widely available online. I like my ball-grip Vessel with swappable bits, even came with Pozidriv bits that came in handy for assembling Ikea stuff.

Philips screws/drivers are designed to cam-out as a torque limiter for ease of assembly without stripping threads, but this can lead to stripped heads with repeated dis/reassembly or trying to undo even a mildly-seized screw.

JIS screw heads look similar but differ, being designed for a more secure fit between the screw head and driver bit; these often (but not always) have a dimple on the head, so that's a dead giveaway you've got a JIS screw, which is pretty much all of them on these trucks. A Philips driver bit engages these even more loosely than a proper Philips screw head, further contributing to head strip-out.

Nearly anything assembled outside the US will be using JIS or equivalent screws, so having the proper driver/bit will help enormously. Better yet, a JIS driver bit also works better on actual Philips screw heads, and a JIS screw head stripped by a Philips driver/bit may still be recoverable with a JIS driver bit.

*Technically superseded by DIN 5260-PH/ISO 8764-1, but outside the industry ppl still call them JIS anyway as they're nearly-enough identical, and only these newer successor standards are readily available anymore anyway.

We should all have a set of JIS drivers ~ thanks SubGothius

this is super helpful, i didn't know about JIS screws, explains all the challenges i've had with TPS screws, coil, etc. with various vehicles. usually end up putting hex-head screws back in!

i've been pretty busy, but getting back to the project now. i did check the timing with the ground-wire connected to turn off the ECU, and it was absolutely steady no matter how much i tried to revv it. revving is hard -- if i open too much, it gutters and drops lower, but if it feather it slowly and carefully i can get it to what sounds like 2500+, with no advance.

so that's definitely a problem, right?

i will say i liked xboxrox's idea of working on unsticking the advance before swapping dizzie's (with potential alignment problems, stripped screws, etc.). but my initial look at it doesn't make it obvious how to do this. any ideas? has anyone had an experience like this?

fwiw, it looks like the PO replaced the distributor recently, it's shiny-looking, and it could be a cheap-o part.

also still would love to rule out fuel pressure as a problem, anyone have a good way to test? (how *do* you attach a pressure gauge to these things? <shakes head>)

thanks again everyone!

Quote:

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Originally Posted by SubGothius

Get a JIS* screwdriver or bit set. Hozan or Vessel brands are good and widely available online. I like my ball-grip Vessel with swappable bits, even came with Pozidriv bits that came in handy for assembling Ikea stuff.

Philips screws/drivers are designed to cam-out as a torque limiter for ease of assembly without stripping threads, but this can lead to stripped heads with repeated dis/reassembly or trying to undo even a mildly-seized screw.

JIS screw heads look similar but differ, being designed for a more secure fit between the screw head and driver bit; these often (but not always) have a dimple on the head, so that's a dead giveaway you've got a JIS screw, which is pretty much all of them on these trucks. A Philips driver bit engages these even more loosely than a proper Philips screw head, further contributing to head strip-out.

Nearly anything assembled outside the US will be using JIS or equivalent screws, so having the proper driver/bit will help enormously. Better yet, a JIS driver bit also works better on actual Philips screw heads, and a JIS screw head stripped by a Philips driver/bit may still be recoverable with a JIS driver bit.

*Technically superseded by DIN 5260-PH/ISO 8764-1, but outside the industry ppl still call them JIS anyway as they're nearly-enough identical, and only these newer successor standards are readily available anymore anyway.

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quick update: took off distributor cap, and attempted to turn rotor. does not move, except some wiggling of the rotor on the spindle. am i correct that rotor should be able to be rotated by hand, on the order of ~20 degrees or something, and then spring back when released? does that happen on your working truck? :)

My 2.6L with Mitsu distributor the advance plate moved quiet a bit of movement too & with just pushing with my finners <g>

Quote:

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Originally Posted by brush

quick update: took off distributor cap, and attempted to turn rotor. does not move, except some wiggling of the rotor on the spindle. am i correct that rotor should be able to be rotated by hand, on the order of ~20 degrees or something, and then spring back when released? does that happen on your working truck? :)

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That would be correct if your dizzy has mechanical advance, but AFAICT from the exploded diagrams in Haynes, looks like the '89-on FI engines had no advance (vac or mech) built into the dizzy at all.

to me it sounds like its jumped time or somehow gotten itself out of time for one thing. The backfiring is a huge give away on that.

thanks, SubGothius, that is super helpful. i also tried turning the distributor rotor on the parts truck, and it doesn't turn either, so unless they both are rusted tight -- i guess there's intentionally no advance? as for the timing being off-- what i think is going on is that the timing was set way advanced previously, and it was kind of working but had low-RPM problems (which kind of makes sense). i then timed it "properly" with a timing light using the numbers on the plastic housing, and it's now got the problems i describe: terrible loss of power when attempting to revv, and backfiring. which i think makes sense if either a) it's not advancing enough with increasing revvs, and/or b) it's leaning fuel (due to pressure or other things). (am i thinking this correctly?)

so -- *could* it be a slipped tooth on the timing belt? which might mean that my timing light-setting is way off? would there be other symptoms?

or could it be that some sensors (which ones?) are causing the computer to send completely wrong advance info? (when the computer is engaged, the timing jumps around randomly within 5 degrees every rotation, it seems like, not sure what that means.)

or, of course, could just be low fuel pressure maybe? claych offered to talk to me about how to test that (thanks), but any thoughts are welcome.

Post up some pictures. They all advance and they all should turn. Something doesn't sound right.

Quote:

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Originally Posted by camoit

Post up some pictures. They all advance and they all should turn. Something doesn't sound right.

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I must disagree ,a fully electronic engine control system with cam angle sensor(S) and a crank angle sensor
configuration does not use or need input from a mechanical device...

I also would like some pictures -- Because I do not know every thing & weirder engineering has happened
Thanks

claych ~ do you happen to know if any years of our trucks have all those angle sensors ? Hope the guy's distributor don't get broke trying to force something that don't supposed to move

As far as I know. None of theses trucks had crank or cam sensors. It was before they came out. Unless someone put in a different engine. This is why when setting the timing you grounded out the plug to keep the ECU from adding advance to the mechanic advance.
once the cam and crank sensor came out we did away with the distributor

No crank sensor needed when the dizzy pickup for electronic ignition is already providing that signal (x4); then it can be static timed without any mech/vac advance, and all advance can be determined by the ECU. From there it was a small leap to eliminate dizzys entirely in favor of crank sensors and directly ECU-triggered spark.

Apologies for the confusion, xbox
I should have been more concise.
I used the word 'configuration' in post seventeen and should have differentiated
between separate individual sensors mounted at the crank & camshaft(S)...
And a single optical 'sensor' mounted in the distributor that provides
a crank and cam position reference signal.(4g64 M/M R/50 , late '88-early '95).

brush? an update?

delayed with all the holiday stuff. need to get back on it though. i don't want to bust anything by trying to force it either! how do i post pics on here, can't see how to do it?

ok, i'm going to try and update with photos to address this question of whether the distributor is at fault.

this photo is of the distributor in the '91:
https://photos.app.goo.gl/rBxFc89ofqSY789y5

you can't see it well, but it's there and a bit shiny, indicating it was fairly recently replaced by previous owner.

these are pictures of the mostly removed dizzy in the '96 parts car, which i think is identical, and also doesn't rotate when i hold both ends (though that's harder to try):
https://photos.app.goo.gl/GmhMdf7jTjFyE8JU8
https://photos.app.goo.gl/b6YuwfJ37TyFvGQYA

back in the '91 here is a poorly lit video of me trying to rotate the rotor, unsuccessfully:
https://photos.app.goo.gl/SF1gFVQ9hedaJq3H7

whatever, just to be clear i'm trying to rotate it by hand, and it slips slightly on its spindle, but doesn't actually move appreciably like one would expect a mechanical advance.

this is a really badly lit video that tries to show the timing (but i think it's impossible to see) and then let you hear the sound of opening the throttle, all with the grounded jumper that takes the computer timing offline. unfortunately the sound has static, but what you would see and hear is: a) fairly steady timing at ~7 deg BTDC, and b) it really struggling to rev up in RPM, actually dropping when i open full throttle quickly, but going up if i feather it.
https://photos.app.goo.gl/b6YuwfJ37TyFvGQYA

and this last is a video of the same as above with the jumper disconnected, ie. computer controlling advance. in this case, the revvs are better and can get pretty high, but still not as responsive as would expect. also, the timing at idle jumps around every revolution w/in about 5 degrees. when revving high the advance is strange, sometimes it goes way advanced as you'd expect, then drops back to just 15 deg or something, then way up high again. not sure if that's expected behavior or not.
https://photos.app.goo.gl/r6kZceUD7vTPhV2d9

thoughts?

Different distributor than on my 1986 Ram50 ~ hm, dark vid & photos I see rusty parts ~ clean clean or order rebuilt ?

I’m. So it’s running but when you hit the throttle it is very slow to respond and back fires, YES?
if that’s that’s the case it’s probably off one tooth on the cam timing. Many times someone will put the belt on and use the flat of the head as the mark or the belt is getting ready to snap. The timing mark is actually below the flat of the head on the passenger side. It’s a bump on the head. It the marks on the crank and cam are lined up and it’s still having problems it might be the MCA jet valves. You can check them with a vacuum gauge. When they go bad the needle is a whip.
If the timing is off 1 tooth the engine will run but but have no power. In the tech section we have pictures of the mark.
also a bad coil will keep it from revving up and can cause erratic timing

Quote:

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Originally Posted by xboxrox

Different distributor than on my 1986 Ram50 ~ hm, dark vid & photos I see rusty parts ~ clean clean or order rebuilt ?

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yeah, mine is a second gen engine, per manual i believe the distributor does not have mechanical advance on the 2nd gen. the dirty one you see is from the parts car -- the one in the worked-on car is newish and clean. i think i'm moving away from the dizzy as the problem.

Quote:

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Originally Posted by camoit

I’m. So it’s running but when you hit the throttle it is very slow to respond and back fires, YES?
if that’s that’s the case it’s probably off one tooth on the cam timing. Many times someone will put the belt on and use the flat of the head as the mark or the belt is getting ready to snap. The timing mark is actually below the flat of the head on the passenger side. It’s a bump on the head. It the marks on the crank and cam are lined up and it’s still having problems it might be the MCA jet valves. You can check them with a vacuum gauge. When they go bad the needle is a whip.
If the timing is off 1 tooth the engine will run but but have no power. In the tech section we have pictures of the mark.
also a bad coil will keep it from revving up and can cause erratic timing

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thanks camoit, this is useful as leads! i can believe that the cam timing could be an issue, but what befuddles me is that the engine was working fine for a while. then a) bad spark wire, b) busted exhaust manifold led to big problems but they kept running it. now those are fixed, but i don't see how doing the repairs on those would have affected the cam timing?? unless it slipped? or, as you say, is stretching and ready to snap?

as for the mca jet valves -- isn't that a 1st gen thing? do 2nd gen engines have them? (haynes says carbureted systems only?)

here's another weird symptom: the revving problem was getting worse and worse. got to the point that i couldn't even get it to rev in neutral, with throttle wide open. switched the MAF with that from the '96 parts car, and it worked better again -- back to the original problem, of really bad power at low RPMs. again, to describe this -- in neutral, it stutters and is slow to rev when suddenly go wide throttle, but if go slowly it revs fine. when driving, going up a hill is hard because the light touch on the accel isn't enough to really make it go. but once you get higher revs, it's pretty much fine -- except for backfires now and then, especially when releasing the throttle.

i'm going to go and test the TPS. when i disconnect it, behavior is basically the same, which i realize might be an issue. ;) going to do the resistance test...

well, just did the TPS test, and i don't know? haynes manual is confusing -- it says to measure between terminals 1 and 4 for base test, where i get 15k-ohms and manual says 6.5k-ohm max. then it says to measure between terminals 2 and 4 for sweep test, but on mine terminal 2 is missing? going from 1 to 3 starts at 5k-ohm at closed throttle, to 15k-ohm at wide open ... so maybe it's describing it backwards?

i suppose i could test the voltage as well, but i'm out of time.

two more notes:

1) i've previously swapped the coil with the parts car, no change. i think that rules it out?

2) i'm guessing it's not the fuel pressure, for now. i rented a fuel pressure tester, but couldn't for the life of me figure out how to attach it without the special very-hard-to-get adapter, or cutting the fuel line (ugh). also, i'm kind of assuming that since it revvs super-high when i get it going, it must be feeding the fuel pretty fast. (is that a bad assumption? is there another way to get a sense of if fuel pressure might be the problem still?)

thanks for the help everyone!

TPS measures the same on the parts car, so I don't think it's that. Argh. How much of a PITA to open it up to check the timing belt on the cam?

Timing belts on Mitsubishi SOHC's aren't "that bad" to get to (at least on trucks...) Requires removal accessory drive belts, fan + water pump pulley and crank pulley to gain access to the timing covers. They're in 2 pieces and the upper half is obviously the easier one to get to. Be aware that there is a small 'seal' that runs around the edge of the inside of the timing cover lower half that goes brittle so be careful during removal.

*tip for cracking the crank pulley bolts - use a deep socket and extension bar with a length of pipe as a sleeve around the bar as an extender. Fit it to the crank bolt and turn clockwise until it rests firmly on the frame (make sure it doesn't rest on anything that could be damaged) Disconnect the main coil lead and crank the ignition in one or 2 very short bursts. Guaranteed to crack the bolt free every time :thumbup:

hi folks, well i got sucked into other projects and just got back to this now. by golly, i think the "off by one tooth" timing belt issue is it. there's a little sticker saying that a new gates belt was installed 10,000 miles ago -- i'm wondering now whether the timing has been off that entire time, and the distributor was intentionally mistimed to get it to run kinda-sorta ok (but off when looking at the timing marks). the timing belt looks clean, no sign of wear, cracks, glazing, etc. so i'm going to assume it's ok, not loosening, and it was just set wrong. (oil pump pulley and crank were in sync.)

so my plan was just to loosen the belt and reinstall one tooth over.

but now, i have a minor puzzle regarding the tensioner:

i loosened the tensioner pulley adjustment bolt, but had to kind of crank on it to push it towards water pump, and it stayed once there -- the spring wasn't pulling it back. no problems adjusting the timing belt, but now it's not clear how to get the tensioner back.

after a little reading around, i see that some sources (unlike the haynes manual) talk about loosening the "upper" tensioner bolt. i'm assuming that this is the bolt attaching the hub of the spring (around which i think the tensioner rotates) to the block? is that correct? my thought is that it's currently very tight and not allowing the spring to push on the tensioner. (the tensioner pulley rotates smoothly, bearings seem fine. i detached the spring and it seems strong. so just seems like that pivot is real tight.)

am i right that this "upper bolt" needs to be loosened? if so, what is it? it's recessed and i can't get an angle to see into it... too small an opening to let a 10mm socket into.

thanks everyone!

ok, an update.

firstly: in some of the cars, the upper bolt on the tensioner is a recessed hex. so... that was easy once i figured it out. so... put it all back together, and now when timing it to 7 BTDC, the distributor adjustment is now perfectly centered! (before it was off to one side). so cam timing was definitely off by a tooth, and possibly had been run for 5 years that way, with distributor timing used to counteract. what damage could that cause? :shrug:

however! this fix resulted in little or no change in the symptoms (!).

i decided to check the spark plugs and do compression test. all the plugs are between 160 and 170 psi dry (though my gauge might read high). however, they're also all dry carbon black -- which is new (when i swapped new plugs in at the beginning of all this, they looked grey-normal). so -- running rich! that also makes sense of the backfires, right?

well, that seems to confirm it's not the fuel pump, but maybe the regulator is keeping pressure high? so i decided to swap regulator with parts car.

however! they say you have to remove the air intake plenum. i tried to remove without doing so, and *almost* could, but could not remove the center bolt entirely. *sigh*. the plenum is a real PITA to take off and put on. some hints: there's 4 bolts and two studs for the mating surface. there's a 14mm bolt underneath on the stay. there's a hidden stay on the inside, above the fuel rail. you have to undo both the bottom bolt (angle wrench required imho) and ALSO the top bolt into the plenum, which is much easier with a long extension straight underneath the TB/rubber connector. then there's a coolant hose underneath, that you really can't reach till you take the plenum off. also, the plenum is designed with a little ridge next to the bottom stay that means have to kind of force it (with a soft prybar) off and on the studs. *sigh*

well, after hours of puzzling through all that (and cleaning the gasket off, etc.) -- the swapped regulator resulted in ... not much difference.

(the one advantage is that i could at least tell that the EGR is a bit dirty but not plugged at all.)

what the heck?

just because, i opened the ECU. no sign of swollen capacitors.

what else could it be? i might try the coil again, but... as i said, already swapped it before with no change.

could this be the O2 sensor? it's running the one from the donor '95, that has the same harness and per rockauto means it's federal emissions, same part. again, that car didn't have this problem...

finally, here's the weirdest thing -- just on a lark, i connected those two harnesses on the passenger side of the firewall, that i believe connect to the tachometer when installed (i don't have one), and the vehicle suddenly behaved ... better. ie. i could rev easily from start. i took it for a test drive, and it was a little improved, like i could drive uphill at 30mph not 15 mph... but still bogging and backfiring. and by the time i got back, seemed to be back to the worse-normal.

what's going on? does that tach connector go to the computer somewhere? is maybe the computer at fault, but invisibly?

any ideas for how to systematically troubleshoot this, it's driving me a bit nuts.

thanks!!

Cat converter partially plugged?

Quote:

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Originally Posted by boozehero

Cat converter partially plugged?

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I've used CATACLEAN product at O'Reilly's ~ follow the directions exactly and it might give great results ~ my truck runs so much better after cleaning out all the carbon from carburetor to tip of tailpipe (kinda pricey stuff tho but worth it IMHO maybe use twice a year...)

thanks for the response! so, a clogged cat was my first thought when all this began. when i originally investigated, i found an exhaust manifold stud was broken, manifold probably warped, and also part of the exhaust connector busted, and so i replaced the entire system from the manifold to after the cat with a donor from the 1995 mighty max donor vehicle. that vehicle had been working fine, no signs of bogging, though was burning oil (and had a busted leaf spring).

again, what seems weird to me about this is that it's able to rev up when i feather it (ie. just barely open the throttle), but WOT bogs it badly. similarly, it actually accelerates briefly whenever i let *off* the throttle, like something is being released. based on the carbon deposits on the plugs, i've assumed this means that when the throttle is opened the mix is getting super-fuel-rich, but i'm not sure why that would be.

i'm also wondering about spark and the ignition system. though the distributor cap looks newish, i'm going to try swapping it and seeing what happens. really appreciate all the ideas, keep them coming!

Quote:

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Originally Posted by xboxrox

I've used CATACLEAN product at O'Reilly's ~ follow the directions exactly and it might give great results ~ my truck runs so much better after cleaning out all the carbon from carburetor to tip of tailpipe (kinda pricey stuff tho but worth it IMHO maybe use twice a year...)

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also, thanks for this suggestion! i might as well try... assuming it also works for injected engines? when i opened the intake plenum, there was a little deposits in the intake but really not that bad, not enough to cause this as far as i can tell, but...

It will work on EFI. I am still thinking there's a fault somewhere else. Have you had any luck trying to pull error codes from the ECU since you've swapped parts? Is the distributor set correctly? I've run into situations where the distributor has been out by '180 degrees' and it's pretty common (it's not exactly 180 degrees due to the odd number of gear teeth) If the O2 sensor wasn't working you'd get an error code from it.

Quote:

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Originally Posted by geezer101

I've run into situations where the distributor has been out by '180 degrees' and it's pretty common (it's not exactly 180 degrees due to the odd number of gear teeth)

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Well, it is exactly 180 degrees, but with the odd number of gear teeth it results in your ign. timing being a half-tooth too advanced or retarded no matter how you insert the dizzy, with not enough range in the advance adjustment to bring it right. This can happen if you rebuild the dizzy with either the drive gear or the mechanical advance mechanism wrong way around.

Quote:

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Originally Posted by brush

<>.... the 1995 mighty max donor vehicle. <>... had a busted leaf spring).
<>

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:shock:WTH?? Outside of an accident I can't imagine how that happens.:confused:

Quote:

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Originally Posted by geezer101

It will work on EFI. I am still thinking there's a fault somewhere else. Have you had any luck trying to pull error codes from the ECU since you've swapped parts? Is the distributor set correctly? I've run into situations where the distributor has been out by '180 degrees' and it's pretty common (it's not exactly 180 degrees due to the odd number of gear teeth) If the O2 sensor wasn't working you'd get an error code from it.

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i've tried to pull codes, and just get the steady blinking light of no codes, as far as i can tell. so probably means o2 sensor is ok? i haven't been able to pull the sensor to test it (or to check the clogged-cat theory more directly), since it's rusted on. my o2 sensor wrench just opens the jaws too much and slips. any recommendations? (i might try the propane torch next).

i'll respond to the dizzy idea next message.

Quote:

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Originally Posted by SubGothius

Well, it is exactly 180 degrees, but with the odd number of gear teeth it results in your ign. timing being a half-tooth too advanced or retarded no matter how you insert the dizzy, with not enough range in the advance adjustment to bring it right. This can happen if you rebuild the dizzy with either the drive gear or the mechanical advance mechanism wrong way around.

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hmmm, the issue is that the distributor hasn't been moved since before this issue arose, when it was working fine. is there a way to tell whether this might be a problem, without disassembly?

you do bring up the mechanical advance again, and remind me of that issue. there has been a debate about whether the 2nd gen trucks have a mechanical advance. when i connect the jumper that cuts out the computer for the timing, there is zero advance with increased revs, even with engine racing. if anything, it very slightly goes towards zero/to the right, about 1 degree or so (i think this might just be that everything's moving so much faster).

can someone 100% confirm whether their 2nd gen truck shows any advance with the jumper set?

that would be amazing, thanks!

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Originally Posted by Lon Moer

:shock:WTH?? Outside of an accident I can't imagine how that happens.:confused:

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yeah, i'm not sure. it was driven that way for many years. maybe overloading it with rock and then driving over potholes?

Quote:

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Originally Posted by Lon Moer

:shock:WTH?? Outside of an accident I can't imagine how that happens.:confused:

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I had a Mitsubishi Lancer 77 fast back that snapped a rear leaf spring. But, they were grossly inadequate from factory and I have a feeling the PO was dumping the clutch in it every time they drove it. When it failed I was lucky I was driving slowly around a turn or it would've killed me...

Quote:

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Originally Posted by brush

you do bring up the mechanical advance again, and remind me of that issue. there has been a debate about whether the 2nd gen trucks have a mechanical advance. when i connect the jumper that cuts out the computer for the timing, there is zero advance with increased revs, even with engine racing. if anything, it very slightly goes towards zero/to the right, about 1 degree or so (i think this might just be that everything's moving so much faster).

can someone 100% confirm whether their 2nd gen truck shows any advance with the jumper set?

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hi folks! one last bump on this. i really can't think what else it is, but throwing more hours (and potential problems) on swapping the distributor when actually it's fine would be pretty painful. i might throw in the towel if i can't get this. :(

i feel like someone doing a check on a 2nd gen with a timing light to see if the mechanical advance moves with revving, with the "ECU cutout" jumper set, would help not only me but others.

thanks!

well, urgent other projects left the truck sitting for a while, but i'm back at it. i removed the crank/cam position sensor from my donor distributor (the 1996 mighty max), with the idea that maybe just swapping sensors would be a great place to start, as a failing sensor would explain the weird jumpy timing light as well as ignition problems. however, the connector for the 1996 is different from the connector on the 1991. does anyone know more about this? also, it appears to be difficult-to-impossible to find the sensor (is it cam or crank or both?) for sale online. anyone know about that? part name?

i guess my main question is: are the sensors compatible? ie. if i cut the wires and splice to the old connector housing, should it work?

(fwiw, rockauto lists the same distributor for both 1991 and 1996.)

thanks!

some updates and requests for help:

after some research, i think crank position sensor is integral in these 2.4 89+ distributors.

so i broke down and swapped the whole donor distributor in. as others before me, had some challenges getting it in the right tooth. i *think* what i realized is that you have to align the rotor to #1 plug at TDC *when the housing is in fully-retarded position*. if you try doing it when the alignment bolt is at the notch (which is close to where the base timing will be), then you easily get a tooth off.

unfortunately, the situation is unchanged with the new distributor. it times to 7deg BTDC when the notch is just about aligned with the bolt. however, backfires and carbonizes the sparkplug. when maximally advance the distributor, it runs much better -- but the advance is way off.

on another forum got the suggestion that advancing timing has side-effect of leaning mix, so perhaps rather than a timing issue this is just a symptom of an underlying running-rich issue. again, having (i think) ruled out the fuel pressure regulator, and with good compression readings, what could be causing rich mix?

thanks folks!

hi everyone! i have some updates.


spoiler: i've tuned it so that it's got 80% of its power back, with only quite rare little backfires! here's how we got there--


i tested the vacuum with a mityvac i have around, and the results were interesting. the main "symptom" is that the needle flutters very quickly back and forth about 1 inch Hg. this *could* be that the gauge doesn't have a damper, apparently, but also might be useful info.


otherwise, at idle and warm the vac is around 17-18 inches. not great, but not bad afaik. rev quickly and release, and it drops to zero then back up quickly to around 23, then settles back. so -- no clogged cat. maybe worn rings. rev high (no tach, but in vicinity of 3k rpm by ear), and it goes down on accel, stays level around 18 or so when even revs, then goes up a bit when decel. seems normal. otherwise, no big issues (eg. spontaneous drops in vac, etc.)


so. if the flutter isn't an artifact, then i think it could mean one spark plug is underperforming, or a valve is a bit tight or got friction or something.


so i start to explore the sparkplugs. bingo - the #1 plug is more carbonized that the others. testing the gap, it's also a lot smaller -- like .030 when the others are .039, which is spec for that plug. (maybe the #1 got bumped a lot as i was pulling it over and over to get TDC correct.)


however -- spec for the vehicle is .044! i check, and the original plugs before i put in new ones are also at .039, so it's been running with subpar spark the whole time.


gapped the sparks, and there's a distinct improvement in performance. can accelerate up hills, much less bucking and hesitation on accel, and much fewer backfires (which only happen at low rpms under load).


so this is exciting!


after gapping the sparks, the flutter in vacuum is less but still present. when i rev high, it sometimes goes away completely, but then back at idle. unlike previously, it seems as if it's mostly at the high point, then once per cycle (ie. per crank or cam rotation) it drops about 1 inch. this makes me think maybe one of the plugs is still acting up, or maybe a valve has problems.


anyone have suggestions for how to further explore this?


at this point, with how well it's now running at correct 7 deg BTDC timing, i'm thinking the timing is no longer a likely cause of remaining problems.


(in related news: on the suggestion above, i thought to clean the MAF. pulled it and sprayed with CRC MAF cleaner, waited for it to dry, then put it back in and it seemed to make things better! wow! THEN i read the fine print that said not to use the MAF cleaner on karman vortex MAFs like in the mitsubishi -- it can destroy them! argh! but things seem fine so far, knock on wood. lucky i have a spare from the other vehicle.)


again, thanks for everyone's input! appreciate further thoughts!

What I would do - replace plugs and under gap them slightly (0.85 to 0.9mm/.033 - .035in) Use NGK's or Bosch. Replace coil with an OEM style transformer type coil with an integrated ballast resistor. I don't remember reading in your posts whether or not you have already replaced it. Blast out the idle air control valve as this has a tendency to mess with idle and power when it's gummed up. Lean on someone who has a hand held dwell/tach meter. Start the engine, put it into ECU tune mode by grounding the connector in the engine bay, loosen the distributor retaining nut and hold rpm's @ approx 2000. Swing the distributor between advance and retard gently until you detect a small spike in rpm and lock the distributor in place. Test drive and observe power delivery. If you think there's a misfire, run the engine in as dark conditions as you can and look for signs of ignition arc. Even attempt to propagate misfire by spraying a light mist of water over the leads and spark plug boots. If I've already recommended any of the above just ignore it lol. I'd also run it on midgrade/89 octane. You should notice a difference between running on regular vs midgrade (better throttle response, smoother power delivery, increase in torque) 91-94 premium seems to nerf torque on cars not designed for it (just my experience and it costs a buttload more...)

*don't use platinum plugs either. Use the recommended rated plug or slightly hotter rated plug to fend off misfire by burning carbon deposits.

Higher-octane fuel is simply more resistant to spontaneous/premature detonation (knock/ping), that's all. For that reason, it's typically specified for engines with a high compression ratio or forced induction (turbo/super charged). It isn't any higher quality, nor has any extra/special additives, nor any performance/economy benefits as long as it's the correct octane specified for your vehicle -- AFAIK, none of our trucks require anything higher than regular 87 octane, but I could be wrong about the later FI engines here (check your owner's manual or look for stickers in your fuel flap or under the hood). If your engine has proper ignition advance and is not knocking/pinging, you probably won't benefit from higher octane and may even see worse performance/economy.

Platinum/iridium plugs are only good for fuel-injected engines clean-running in good tune and not burning much if any oil. Otherwise, they just tend to foul quicker, as they have less surface area in the spark gap. The tradeoff advantage for that is greatly reduced wear due to the harder electrode metal and thus extended replacement/regap intervals (if they ever need it at all). Use conventional plugs while getting your engine into good tune, then feel free to switch to platinum/iridium if it's injected.

As for running cooler/hotter plugs than specified on a stock engine, that's just a band-aid for symptoms without really solving the underlying problem causing those symptoms. Here's a good overview I found about plug heat ranges. I suppose if you're burning oil and can't feasibly fix that anytime soon, running plugs one step hotter might help burn off the oil fouling the plugs.

My Gen 1 truck has the G63B 2.0 in it. On the fuel filler door there's a decal stipulating 97+ octane fuel but I bet every owner cheaped out on it and filled it with regular pump. It seems like a pretty exotic fuel to use in a 4 cylinder truck made in the mid 80's. This isn't a feedback operated carb and doesn't have an O2 sensor in the exhaust - Australian delivered trucks 'may' have a higher CR but I don't know/doubt it. I use the equivalent of premium in my Hyundai beater wagon. There is a definite difference in engine behaviour compared to regular pump (bearing in mind this is a 16v twin cam 2.0). It idles and runs smoother, has better throttle response, more torque and improved power all round. I have tried using 98 in it and it felt down on power and torque (not what I expected). It still idled and ran as smooth as 95. Only way to get the best performance out of your engine is to test different fuel and tune combos...

Ah yeah, US-market engines in general (esp. those still carbureted) often had a nerfed CR during that era to help meet tougher NOx smog standards; RoW models likely differed with a higher CR that may require higher octane.

Also, octane rating standards can differ by country, so that 97 RON octane in AU would be equivalent to about 91 (R+M/2) octane in the North American market.

...wonder what they did to bump CR's to the OEM engines :think:

It will be timing limited probably

thats the case on my nissan, its a JDM import so its running quite a lot more timing than the ones that went to the usa. Better fuel and giving them more timing gives the USA ones more power

retarding the timing reduces the dynamic compression ratio, so less pressure on the intake mix, so less preignition

Quote:

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Originally Posted by tortron

It will be timing limited probably

thats the case on my nissan, its a JDM import so its running quite a lot more timing than the ones that went to the usa. Better fuel and giving them more timing gives the USA ones more power

retarding the timing reduces the dynamic compression ratio, so less pressure on the intake mix, so less preignition

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Makes sense. It seemed like the plug gaps on US factory tune specifications were... generous. So retarding the timing and adding a big plug gap (1.1mm?) will seriously affect power output and make the requirement for higher octane fuel unnecessary.

OK so here are the factory tune specifications for Australian market G63B 2.0 optioned trucks -

13 deg BTDC+/-2 deg @ 700 rpm +/- 50 rpm

plug gap 0.7mm - 0.9mm

*and a link to a review of the lowest mileage L200 on earth - https://www.drivesection.com/reviews...xpress-review/

It's the base model. It has vinyl flooring and the small side storage boxes under the bench seat. No clock, AM radio only and no A/C.
And - it's perfect :green:

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Originally Posted by geezer101

...wonder what they did to bump CR's to the OEM engines :think:

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Typically most mfrs. just used lower-compression pistons in their US-bound engine builds during that era.