91 GMC Jimmy stalling

[tonyjor]

Hey everyone. I have a 91 S15 Jimmy that's been acting up and I'm just wondering your thoughts on what it could be. It's been idling sporadically and it cuts out sometimes while I'm driving. It only does it for a second, like there's an air bubble in the gas line. My guess is the fuel filter. Would a fuel pump going out make these symptoms happen? Or do fuel pumps in Jimmys just quit working all at once. It's been about a week that it's been doing this. Thanks for any insight.

[YukonDew]

4.3?? How about your gas mileage? If it sits for a while do you have to crank it two or three times before it starts?

Sorry for the third degree, but I've been in Jimmy's/Blazers for a while and I've run into a few different problems - mostly fuel related - and a little more info might help. Send me an email if you like, I might be able to shed some light on it. tgparts32@hotmail.com

[john.wells]

could be a number of things, is there a service engine soon light on? I would suspect a throttle position sensor problem with the little bit of info provided, but a myriad of sensors or wiring problems could be the cause.

[upnorth]

You would amazed how much some injector cleaner can help if the injectors are starting to plug up. Run a good cleaner for a tank or 2 and it may help and not cost a whole heck of a lot.

[Valv]

The 4.3 CPI had many issues with the injection "spyder" lines inside the intake.

I had one myself and I replaced whole unit with a new one (bought on hsolist for $ 100) instead of $ 450 ad dealer.

It's not a tought job to do, but we need more details about sympthoms.....

[Dan Thiem]

Hey Tony! I remember meeting you at the portable mod deal up that way. I can also help shed some light on your dilema. Shoot me an e-mail. dt@vikingolds.com

[Jeremy airjer W]

Tony, does the speratic idle occur all the time? Is your brake pedal really hard when the problem exists?

[brian6715]

I had a 4.3 blazer, it did that every now and then, but some injector cleaner would fix the problem everytime for about 2 months.

[MnIceman]

It's water in the gas. At least that's what I've been experiancing over the last month. My truck was the worst at it and the check engine light would come on with a "misfire cyl.4" code. I went through everything, plugs, wires, cap, rotor,checked for vacuum leaks,checked injectors and wiring harness, checked all the sensors, fuel pressure and leak down test. Everything was great. Tried injector cleaner and it ran worse at an idle . Always had been using the same gas stations here and up north. Was talking to my cousin up north and he said that they were having a water problem at that station up there. So I filled up at a different station and put in a couple of bottles of isopropyl alcohol. It ran great and no more engine codes. A couple of tanks later I tried that station again and the problem was back . My other cars had similar problems but not as bad . Bought a case of that Isopropyl and add some to each tank fill and no problem. I thought that this ethanol was supposed to take care of it, but apparantly there is more water than it can handle.

[tonyjor]

Wow! Thanks for all the replies. I changed the fuel filter and it's still doing it. I noticed it happens more when I'm going about 60-65 in OD. It happens out of overdrive too, but more during. It also happens only when the engine's warmed up. It runs great while it's cold. I checked the plugs and they all spark, I tried the isopropyl with the last 3 tanks of gas and I gas up at different stations a lot. I pulled the wires off the injectors on the throttle-body and it makes it run worse, so I know they're working. I took the dist. cap off and the rotor looks good, and should be if all the plugs work. Is the fuel pump mechanical on GMC Jimmys? I'm starting to think that's what the problem is but i always thought they went out all at once. Thanks for any more help!

[deadeye]

Have someone run a diagnostic on it, there are a couple of sensors that could give you trouble when it warms up. The idle speed control could do it, egr valve, oxygen sensor, and some others. The fuel pump on that truck is in the tank and they are also kind of fussy. My bet is that the fuel pump is to blame but there are so many sensors that it is hard to tell without putting a scope on it.

deadeye><>

[tonka]

since it happens only when its warmed up i would definetly check the egr valve. you can try this site too, www.allexperts.com

[john.wells]

I would rule out the fuel pump because it would be acting up under any conditions. Fuel pressure regulators are a common problem to check. If there is no check engine light on, this could very well be the culprit.

[tonyjor]

Where is the egr valve? Also, what is an egr valve? I've heard of them but I have no clue what they do or look like. The check engine light isn't on, so I'm thinking it's not a sensor causing the problem. Thanks again for all the help!

[Jeremy airjer W]

EGR valve is an Exhaust Gas Recirculation valve. Basically It recirculates exhaust gas through the combustion chamber. This Reduces oxides of nitrogen (emissions). Cools down cumbustion chamber tempratures which helps reduce ping.

If you have a 4.3 liter, which is really common for carbon chunks to get stuck in the pintle of the EGR, its located right under the throttle body. It should be a silver cylinder with wires going to it. Two ten mm head bolts are all that hold it in.

the sympton would be poor if any idle and possibly an extremely hard brake petal. The EGR only comes on during excelleration. If it is stuck open it becomes a huge vacumm leak causing the poor Idle. The only reasonable fix for this is to remove the EGR valve, Remove the chunk of carbon stuck in the pintle, and install a new gasket with a built in filtering screen to prevent the chunks from getting stuck again. There are also some PROM updates for some vehicles which can help also.

The 2.8 liter (I think this was an option in 91) also has an egr but I cant remember where it is or what style it is (vacumm or electronic). Its been a long time since I've seen one of those, Wich is a good thing!

[Macgyver55]

I didn't see this thread earlier or I would have replied. For some reason the EGR problem AIRJER described was common on this particular motor. The nice thing is that it is a very easy fix for most anyone at very a minimal cost. No special tools needed either. Hopefully it is your problem.

[tonyjor]

Airjer, congrats on the fish! Thanks also for the EGR valve description. I'll get a new one tomorrow and try it out to see what happens.

[Jeremy airjer W]

tonyjor,

Thankyou!!

The EGR valves in the 4.3 rarely go bad! The carbon gets stuck in them if thats the case you would deffinitely know. They are also not cheap, considering it may not work, so if the above symptom doesn't match your problem, which it doesn't seem to, then I'd hate to see you possibly waste your money.

I would like to see what kind of info you would see on a scan tool. I'm leaning toward possibly a pickup coil/distributor. The info on the scan tool at idle would possibly have some really funky engine load numbers.

If at all possible try to elaberate on the symptom at idle. Is it running ruff like a dead cylinder, sputtering (put put put......put put........put......put put put Thats pretty good), is the idle going up and down really fast, or is it just barely running (rpms really low). These would be some valuable clues.

[tonyjor]

The EGR valves are about $70, so I'm going to take the truck in and have it hooked up to the diagnostics machine. After all this time of it happening, I've narrowed it down to happening only when the engine is warm, any speed(even stopped and idling) and it's sporadic, which means it is firing but maybe I have a semi-bad plug? It's almost like it goes out of time and then back, over and over. The worse part is when I go to take off from a complete stop, I push in the pedal, it starts moving, cuts out hard like it's going to die, then goes okay for 30 seconds or so, then cuts out, goes 10 seconds, cuts out, etc. When I can find the time I'll be heading to a shop. Does anyone know of any shops around St. Cloud that do free diagnostic tests?

[Jeremy airjer W]

WHAT ENGINE SIZE DO YOU HAVE?

Here's something to try. Start up the vehicle and spray the ignition wires, coil, cap with water. If you see or here spark jumping to ground or the engine stalls you have just narrowed down the problem and saved $ by not paying a shop to do the same thing. If you don't see anything powerbrake it (while everything is still wet in a safe area where you won't hit or run anything/anybody over! This may duplicate the symptom you have described consistantly. A major tuneup (cap rotor plugs wires) is not that difficult on these.

I know that you checked for spark but bad wire may not show up unless there under load (high secondary resistance).

A couple of tips. use A/c plugs! THE CHEAPER THE PARTS, THE CHEAPER THE PARTS. I've had good luck with Standard Ignition parts and the NAPA brand. The bolts that hold the cap on can break so be carefull.

[tonyjor]

oh, sorry, all these posts and no engine size. It's the 4.3.

[Jeremy airjer W]

Any updates or fixes tonyjor?

I had a 92 blazer 4.3 litre last week. Would run o.k. for five to ten minutes from a cold start then get an erratic idle and would almost stall. It took about 30 seconds to clear up then ran great? Luckily enough I figured out it would only do it as soon as the ECM swithed from open loop to closed loop. It stored a code 51 Prom error. Step one check all connectors/wiring at ECM, if o.k. replace prom. If that doesn't work replace ECM. I swear that was the diagnostic flow chart for this code. The new ECM took care of it!