Need some help, Backfires when given gas.

Hello all,

My 86 2.0 3spd is having some weird issues these past 2 week.

I hadn't drove it for almost a month now and went to start it, started just fine, idled just fine. Let it warm up and put it in gear, got out of driveway and stepped on the gas and it backfired out of the carb. Wouldn't go past 25 mph. Hasn't had any issues for the past 2 years.

Pulled back in and started working on it. First was to double check firing order and that was all set right to 1-3-4-2. PCV was good. Set a timing light and timing is all good there and checked it at tdc on the compression stroke and everything lines up. Distributor advances like it should, and it's vacuum advance diaphragm holds vacuum, and I get vacuum from the hose. Cap and rotor are also new. I then did a compression test on it and all 4 cylinders are at 150 psi. Checked around for vacuum leaks also and nothing came up. Also replaced fuel filter.

With it running I pulled one wire at a time and gave it throttle, it would backfire and stall on 1, 2, 3 but would rev fine and did not backfire when I pulled #4. Thought okay, maybe a bad wire and got a new wire set, plugs, and coil, but nope, still the same issue. Pulled the valve cover off, ran it without that to see if something was sticking but nothing was and everything looked to be running right and if a valve was not seating right, the psi in that cylinder would be low I would think.

It's not burning oil or coolant.

The only other thing I can think is that something on the carb went bad or Egr? Maybe Tps or O2 sensor? I'll test the o2 and egr tomorrow

Something else I should add, is I noticed before I parked it that it bog quick once after a while in and out of gear at idle after a minute or so kinda like vr-vr-vr-ch-vr-vr-vr (Yeah ik, I'm explaining sound via text LOL :))). Also one time I had to start it with my foot pressed all the way down on the gas, so maybe the Tps is going/went bad?

Any help would be appreciated.

My buddy and I have been scratching our heads over why it decided to start doing this. It had passed smog just fine in October..

Thanks,
Fenster

What are all the vacuum lines like going the vac control unit? Seems to be the leading culprit with idle/power issues. Weird...

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Originally Posted by geezer101

What are all the vacuum lines like going the vac control unit? Seems to be the leading culprit with idle/power issues. Weird...

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All the vacuum lines themselves are pretty new and not cracked where replaced 2 years ago with some 3.5 mm and 4 mm vacuum tubing. Everything was hooked up right, maybe the guy who did the smog did something by accident? Idk. But yeah idles great, but step on the gas and it backfires.. I could post some pictures of the nest of tubes, everything looks to be hooked up right via the diagram.

cap & rotor contacts "crusty"/tired....or just some condensation inside the cap?

did you check the lines going to the silver box on the drivers side inner fender - that houses the vacuum sensor for the computer controlled carb. The lines crack inside there, especially the big one going to the sensor, and it will bog and backfire if that hose is split.

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Originally Posted by ragragtimetime

cap & rotor contacts "crusty"/tired....or just some condensation inside the cap?

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All of that checks out good clean contacts, no condensation.

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Originally Posted by pennyman1

did you check the lines going to the silver box on the drivers side inner fender - that houses the vacuum sensor for the computer controlled carb. The lines crack inside there, especially the big one going to the sensor, and it will bog and backfire if that hose is split.

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My truck doesn't have that box, never seen it with one, it was made 04/86 if there is any differences. Tested every hose with a vac gauge and they all pass. No cracks in the hard plastic ones either that run along the firewall. Here is a picture of whats on my driver side fender.
Attachment 19951

I have the distributor disconnected right now also just to add lol..

What do the spark plugs look like? Are they showing signs of the engine leaning out? And is the secondary throttle actuator working? If the vac actuator is split you will lose all of your top end and it will create a vacuum leak in the process. Take the elbow hose off it and hook up a longer hose and try sucking on it. If you can pull continuous air from it, then the actuator is kaput.

you are cali emissions - that explains the difference. Try Geezers suggestions it sound like a vacuum leak

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Originally Posted by geezer101

What do the spark plugs look like? Are they showing signs of the engine leaning out? And is the secondary throttle actuator working? If the vac actuator is split you will lose all of your top end and it will create a vacuum leak in the process. Take the elbow hose off it and hook up a longer hose and try sucking on it. If you can pull continuous air from it, then the actuator is kaput.

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Took a look at the old plugs, and they looked to be rich, not lean.

Tested the secondary, and it seems to have a leak...again :( , so that might be it.., but why did it last only 2 years? Just curious since that's the issue I had 2 years ago, only without it stalling thrown into gear, but instead it's backfiring.

Also how stiff should the secondary throttle be? Mine seems to be pretty stiff to move.

My secondary looks like this one. Should it be that type, or this one ? I had the carb rebuilt 5 years ago, maybe they used the wrong actuator?

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Originally Posted by pennyman1

you are cali emissions - that explains the difference.

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Why you got to remind me of my misfortune of living here? Are you saying my truck is special and different from the other out of state trucks? :lmao: Sorry, had to :P:grin:

The secondary is locked out by a cam lobe on the primary throttle shaft. That way the vacuum prevents the secondary from opening before the primary has reached it's midrange power band. It should move freely once the primary is completely open. I think the G63B carb should have the spring tensioned actuator on it, not the metal arm. But I can't be 100% sure due to the Cali emissions thing. It was running fine before right? And now you can confirm the secondary is leaking. Damn, those secondary diaphragms are not cheap either...

Happy Holidays All!,
Ok so its been a few days with the holidays and all.

Got around to pulling the secondary actuator off, and put a spring in just to see how much that had fixed it. Plugged all the old lines that ran to the secondary and started it. Started up just fine and didn't backfire.... as bad. It will idle just like it did fine and all, but sometimes now when you give it gas it will backfire.... But it doesn't want to stall like it did it seems..

Oh and did I mention that I now have a tick that increases with the rpm now since I fixed one issue...? Well I do now.
:lmao:dang lol...

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Originally Posted by geezer101

And now you can confirm the secondary is leaking. Damn, those secondary diaphragms are not cheap either...

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I think I will leave the spring I put in there for now just until I get it running and driving right and not backfiring.

OK I got something new to add. My friend tested the O2 sensor and it is working how it should. HOWEVER at idle it is doing what it should (bouncing back ~1v-0v) but once it's off idle and open throttle it will Lean out. Hope this info helps. Wish I tested that sooner. Gave my friend a book to take home and he and I are looking at what to probe next. Whatever is causing this may probably be the main reason on why it backfires.

Btw it no longer ticks/ pings, I enriched it a tad and that went away.

Things are starting to look somewhat better! :))

Sounds like you may have more than 1 issue with the carb. Has it been overhauled? Take the air cleaner off, pull the throttle open and closed and look down the primary throat for a shot of fuel that should be coming from the side of the venturi out of a small jet. No fuel = accelerator enrichment pump is dead. If you see a trickle of fuel that means it's blocked. What fuel are you using and are you using the factory recommended tune? The factory tune is garbage.

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Originally Posted by geezer101

Sounds like you may have more than 1 issue with the carb. Has it been overhauled? Take the air cleaner off, pull the throttle open and closed and look down the primary throat for a shot of fuel that should be coming from the side of the venturi out of a small jet. No fuel = accelerator enrichment pump is dead. If you see a trickle of fuel that means it's blocked. What fuel are you using and are you using the factory recommended tune? The factory tune is garbage.

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Whole carb was rebuilt 5 years ago and ran fine until now.

It shoots fuel strong when you pull on the throttle.

Fuel is 89

Not sure on the tune, I'd imagine factory just since it was rebuilt by a shop.

Oh and I noticed idk why I didn't bring it up before, this never looked right to me, but could not compare it to anything. When I was a younger and my father owned it, looking under the hood out of boredom lol, I would swear that these two ports had something going to them, but since it was rebuilt they where plugged... But can't find any info, I had a shop re-install the carb 5 years ago... If I would have to guess maybe the fuel line from the return on the fuel pump went to one then the other one to the return? I bet this could be the culprit....
If anyone knows how it should go then let me know.

Attachment 19963

Just by pure luck I found this image on google that directed link to this post on...mightyram50 -

http://www.mightyram50.net/vbulletin...ll=1#post17915

Is this what you're talking about? There's a fuel barb sticking out on an angle that crosses the path of the main fuel inlet line and another pointing exactly the opposite direction on the other side of the accelerator enrichment pump. If I'm getting this right, the shop bypassed the accelerator pump and hooked the line straight up to the fuel return line - which is bad and stupid on the shops behalf.

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Originally Posted by geezer101

Just by pure luck I found this image on google that directed link to this post on...mightyram50 -

http://www.mightyram50.net/vbulletin...ll=1#post17915

Is this what you're talking about? There's a fuel barb sticking out on an angle that crosses the path of the main fuel inlet line and another pointing exactly the opposite direction on the other side of the accelerator enrichment pump. If I'm getting this right, the shop bypassed the accelerator pump and hooked the line straight up to the fuel return line - which is bad and stupid on the shops behalf.

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Yeah that't it!:)) I think I saw somewhere that, that is a return hose in that pic. But I think I remember something also being hooked up to that other port on the right in my pic. Does the fuel pump return go to that, then the return on the carb go to the tank? Dare I ask what the shop might have broken lol? :shakehead:

The line that is now hooked from the pump to the return hose is meant to feed into the forward facing fuel hose barb (this is the inlet for the accelerator enrichment pump) and the other barb connects to the return line. Those monkeys... Without the accelerator enrichment pump you will have a flat spot on take off. But be warned, there might be a reason why it's not connected (your pic does show a new diaphragm gasket poking out around the top of the pump). Reconfigure the hoses so they are correct and see what it does. Use the method I suggested in my earlier post to look for the tell-tale stream of fuel coming out of the enrichment jet. If the pump is functioning and all the diaphragms and gaskets are new, it will shoot a solid jet of fuel straight across the primary throat in the carb.

I'm going to be a happy camper if this fixes my issues :)) .

Kinda weird it never showed the sign of it running like it does now over those years without those lines hooked up. Wonder if I will feel a noticeable difference in how it preforms and if I can go over 16-19mpg... I was using it more this year than the others because of some projects I have going on, noticed capy gas mileage as well.

I would go out in the cold and dark midnight sky and do it fast but the neighbors might not like me celebrating and reving it lol... I'll report back in the morning!

Great, I doubt I can sleep now hahaha.

Thanks!

Try retuning the engine using this method - http://www.mightyram50.net/vbulletin...ll=1#post56600

I know you are hog tied by the Cali emissions thing but this should help with engine performance. The new coil and ballast resistor will ensure you get a good mixture burn. Make sure your plug gaps aren't too closed up as well.

Well, hooked up the lines like it should and followed the advice you listed , but my issue is still there :shrug:... Only now it "hiccups" at idle when warm and when you start it the EGR Light comes on and will go off and stay off if you rev it to about 2000 rpm...

Are there any other adjustment screws on it that are not so visible? Also it seems the engine is bouncing between +- 200 rpm at idle.

I looked down the carb and noticed a little amount of fuel in the manifold.

I'll try and hunt down for the 5th time vacuum leaks but I doubt that's whats causing it.

Oh and there's this white wire on the coil, something ticks for a second on the carb once it has power. I'm just curious, what does it go to? Part of the O2 sensor? can't find a white wire listed in the wiring diagram. I don't have a tach gauge.

Is there a black wire with a white stripe on the side of the carb that is/isn't hooked up? It's for the fuel cut solenoid. This bad boy needs to be hooked up or it'll shut off the internal air metering in the carb and do things like randomly kill the engine (or perhaps in this case mess up fuel delivery enough to cause it to run badly) It is powered by the ignition circuit - no power, no fuel.

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Originally Posted by geezer101

Try retuning the engine using this method - http://www.mightyram50.net/vbulletin...ll=1#post56600

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So I got to working on it again.

Looked at the wiring diagram, though its a white wire in the book it says it's black..? But I found the cause of the backfire was that the coil was hooked up wrong, the blue wire on the distributor and that white wire where on the positive coil and the resistor plus a black/white wire were on the negative. Hooked up the wires how the book said (Blue and white to negative, all black/white stripe wires on the resistor and resistor hooked to the positive.) Fired it up and It ran first shot and didn't Backfire... But it stalled when given throttle.

Thought ok fuel delivery maybe. Changed the fuel filter and nothing different happened, tweaked the fuel mixture and nothing happened.

Then got the idea you gave me, ignition advancement (one thing I didn't follow yesterday:grin:) , took the distributor out and moved it a tooth to the right, popped it back in and it fired up first shot.

Thought naw, can't be, popped it in drive and gave it throttle and BAMM IT DROVE, no backfires or stalls! :))

It does however have a little 1-2 sec of hesitation when you hammer the throttle and feels like it might stall if you don't let up, but once it gets past that it drives fine. I think a little more tuning is in order and it will be running 100% better than it has in 5 years lol...

If we can rid it of the hesitation it has it will be golden!

Happy New Years!:))

Make sure that accelerator pump in the carb is working. This is a symptom that it's not getting the little extra boost of fuel off the mark. But even if you go hard open on the throttle, the carb won't be able to keep up with the sudden increase in vacuum. The Mikuni is a slug and you have to 'feel' your way into the power curve. Give my tune method a try (I know you are subject to Cali EPA crap) but you can always re-set it when it comes to inspection time. If you can get the ignition to follow a similar curve to the throttle butterflies opening, you'll unearth some useful midrange power and improve your highway cruising top speed.

:clap: Well done to you for persevering. It sucks when you keep hitting a wall and can't get around it. The biggest issue you had was the coil wiring and the distributor being out a tooth. It didn't help that a workshop couldn't even hook up the fuel lines properly and took a short cut just so it would run.

Thank you!

I have been reading your advice and by luck I found this guys thread as well http://www.mightyram50.net/vbulletin...-for-smog-Help.

I think my choke needs to be adjusted a tad, it's closed up tight when sitting and has some tension on it that a "light tap" can't easily open it when cold.

I'll see what I can do to it tomorrow.

Thanks again for your help!

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Originally Posted by geezer101

The line that is now hooked from the pump to the return hose is meant to feed into the forward facing fuel hose barb.

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Well, was running for a short time fine but still had a flat spot. Ended up taking it apart and found a diagram for the (vent system??? 3 screws holding on a solenoid of some sort towards the valve cover side) was cracked and the cast piece was in cracked in half. That was allowing fuel to go from the bowl, straight into the vacuum. Prob explains why I was getting a consistent 250 miles per tank. Got a rebuilt crab and hope for the best on it. But yeah that gasket looked like it wasn't replaced, and when the cast piece was cracked when it was rebuilt, they prob didn't bother doing anything and put it back broken.

For the accelerator pump, did you mean the fuel pump hose gets connected to the "forward facing" fuel barb on the right side or the one in the front, to me they are kinda both can be forward facing lol... Ran the same hooked up either way it seemed on the old carb, but slightly better, Sorry, I just don't want to blow anything on the "new" one.

Just wanted to share what I found out.

Thanks.

The accelerator enrichment pump is the square block on the side of the carb with a fuel line in and out. Top barb is from the fuel pump, bottom barb goes to the return line. The primary and secondary fuel feed lines (from the pump) are different diameters (primary/fuel bowl line is obviously the bigger diameter hose). It wn't kill the carb but the engine won't run right if they're swapped.