Acceleration stalling & backfire????
 

I have an '89 B2 XLT 2WD w/2.9 and I can not seem to figure out what is causing the following.....

It starts fine, has only a slight idle miss, but when I accelerate it stalls, stutters, and then backfires before finally speeding up. At idle, it will sometimes slowly begin to idle erraticly, idle down and struggle for a few seconds before finally shutting down....this doesn't always happen but it does happen. While driving, if I really goose the petal it will only stall and then go, but not the best thing to be doing at daughter's school with lots of people around. The code plug-in connectors seem to have been removed from under the hood so they are no help.....I only bought this a couple months ago and just discovering the wonderful care it has received in the past. Also, when using cruise it will stumble then surge every 8 or 10 seconds, and all speeds....sometimes it sputters here as well, but not always.

The MAP and TFI are ok, and I have replaced the plugs, wires, the dist cap and rotor are good. What I can't figure out is if it is a fuel or an electrical problem. There is plenty of spark and fuel pressure. Something I am wondering about......when the IAC wires are disconnected the idle does not change at all. What is supposed to happen? And can a bad IAC cause all this?

My test equipment is rather limited so any suggestions as to what to check would be greatly appreciated.

It seems that the best first step on these engines is to run the EEC-IV self-tests (aka "pulling codes") to see what problems the computer sees.

Have your Cat checked... if not, try your ignition module on the back of the distributer.... (7mm socket needed)

Do you have a CEL?

Are there any wires over by the power distribution box that don't go anywhere?

Please forgive my stupidity, but what is a CEL? And there are no connectors near the the Dist Box that are not plugged in that I can find.

Cat seems fine, no bad smells from either one and the rest of the exhaust looks good too. I checked all the way up to the motor. Nice and tight and fairly new looking even.

And as far as running the codes, as I stated prior...and I'm only guessing but....the test connectors have been cut off. I say this because along side of the fender and under the heater core they are laying. One clearly marked EEC TEST.....Just the connector with no wires.

After some checking I was able to detect a very soft "whistle" when the accelerator is first pressed. It is very quiet but it's there, from somewhere in the engine compartment. When I very gently press it the faint "whistle" starts and then the next little bit down the erratic idling starts and it begins to stumble. and bog down. This may be noting at all but just thought I would mention it.

Also, when I turn sharply to the left I can hear "something" clunking in the rear of the vehicle. I've checked inside, outside, and under and have no idea what it is. Could the in-tank fuel pump have possibly come lose and be causing the problems I'm having?

When I first got the B2 it was running sweet and didn't have a miss at all.....Not any problems at all. Then one day I decided to put $20 of 92 octane from Chevron in the tank instead of Chevron's 87 octane that I normally used....to help "clean out" the injecters and the fuel system....so I thought. I drove about 5 miles when it started surging really bad, down-shifting, sputtering, backfiring, and trying to stall out (like it does now). It's been doing this same thing ever since that day, although not quite as bad since I've ran a few Fuel Cleaners through it. It's drivable but bucks like a wild pony at in-town speeds.

Those two plugs should have been hanging right by the power distribution box, did you check for the wires that would have connected to them around that area?

Sorry, CEL = check engine light.

No loose wires that I can see. I believe the past owner must have had stock in an electrical tape company.

And no CEL. I do get the battery charging light on every now and again but the Alt seems to do ok with the battery disconnected and all the grounds are tight....and the battery is less than a month old.

Get a wiring diagram and pin assignment list for the EEC-IV 60 pin connector (Is this something you have access to, Ken00?). Locate the STI, STO, and SIG RTN leads that would go to the self-test connector. Then, either trace them out to the fender under the hood and hook the connector up, or cut these wires and wire the self-test connector in somewhere else (under the dash seems like a good possibility).
Like I said before, the self-tests seem to be the best place to start. If it were my truck, I'd get the self-tests working before chasing down other paths.

My 1989 diagram show pin 17, t/r wire, as VIP output (STO), this is were you would connect a meter. Pin 48, w/r wire, the single wire at the PDB (STI). Pin 46, bk/w wire, as sensor ground ( SIG RTN). Read this over mrshorty, make sure it sounds right, those wiring diagrams are hard to read anymore, I must be getting old.

I ran 8 ozs of SeaFoam into the intake through the brake booster vacume line this morning and then shut it off. As it was being vacumed in, there was this HUGE cloud of white smoke that started up. As soon as the 8 ozs was sucked in, I shut it down and poured the remaining 8 ozs into the tank (with about half a tank full). I let it set for about a half-hour and then took it for a little drive. I was surprized that upon restart there was hardly any smoke at all. After about 2 miles the idle settled down somewhat and the stalling/backfire was all but gone. The surging while using the cruise is still there however. I'll be convienced of SeaFoam's worth over the next couple days if the current success continues but it sure has helped in the short-term. I'm going to repeat the process when this half tank is gone.

So....it seems to me that the bulk of the problems I have been having are fuel related. I guess that when I put the $20 of Chevron's 93 octane with Tecron in it must have knocked something loose and plugged one or more of the injecters and/or possibly crudded up the fuel system. I know it's not over yet, but it's nice to at least see some light at the end of this tunnel of repairs. I'm having a local shop reinstall the code plugs and then I'll figure out what else is going on.

Thanks for letting us know how things are going, glad to hear you making progress, keep us updated.

I discovered this morning that the SeaFoam didn't help as much as I thought it did....Still sputtering, backfiring, surging, and stalling.

One thing I did for the temporary is I pulled the small vacume hose loose that runs from the air cleaner compartment to the intake vacume tap. With this loose I found the idle is smooth as silk but running about 1300 RPM's in Drive, and almost 1800 in Park or Neutral. A little sputtering but no backfiring, stalling, or surging, although there is a very noticable decrease in power. Being a 2.9, how can I idle this down? I know the vacume hose being removed is a bad idea but had to do something to get home. Could this possibly be a sign as to what is wrong?? Any ideas???

Woke up this morning and put on the work coveralls. I crawled under the B2 and started checking things out. I found that the bottom front cat heat shield was loose. I started wiggling it to see what happened and it fell off in my hand. The rear cat bottom shield is also loose on one side. The system seems to be in "ok" shape otherwise. No holes, unusual sounds, or exhaust smells other then from the tailpipe.

I then popped the hood and started looking with a fine-tooth comb. I found an open vacume nipple on the bottom of the TB. I have no idea where this is supposed to connect to so I just plugged it. Also, on the air filter cover, I switched the 2 small vac lines around and low and behold, the IAC opened up and in went the air. I disconnected the IAC electrical and the engine stumbled and nearly stalled. I reattached the connector and it improved. The idle improved until a little later when the engine warmed up fully, then disconnecting the IAC electrical seemed to have no effect at all. The idle still has a miss, and is a bit low (800 to 900 RPM's in Park) but there are NO backfires and only a slight sputter and stall when driving at low speeds or from a stop. I removed the canister thingy (connected to the air filter cover via vac line) from the system completely and it seems to have no ill effects.

And the B2 Battle continues, but at least I do seem to be gaining some ground.

I think one of theose nipples goes to the inlet air for the PCV system on the drivers valve cover and the other one comes from the valve, could be wrong, it's been awhile since I work in the 2.9.

The vacumm line to the air filter is for the warm air valve, I would check the system for a vacuum leak and put it back in the correct locations.

Overall I would work on pulling the codes and not disconnecting things, just MHO.

Ok, I ran the codes....twice even to make sure I got everything. Here's the results.....


KOEO - 11

Con Mem - 41

KOER - 13, 72, 73, 74



I have a Haynes repair manual and know what the codes mean but that's about it. Now what??