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

[brush]

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

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.

[brush]

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

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...

[brush]

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!

[brush]

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?

[geezer101]

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

[brush]

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!

[brush]

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?

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!!

[boozehero]

Cat converter partially plugged?

[xboxrox]

Cat converter partially plugged?

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...)

[brush]

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!

[brush]

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...)

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...

[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.

[SubGothius]

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)

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.

[Lon Moer]

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

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

[brush]

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.

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.

[brush]

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.

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!

[brush]

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

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

[geezer101]

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

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...

[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?

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!

[brush]

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!

[brush]

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!

[brush]

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!

[geezer101]

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...)

[geezer101]

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

[SubGothius]

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.