Help me please

[87silveradok20]

So I have a 1989 k30 with a newer crate 350 in it with Tbi on top. It will randomly cut out and die. Sometimes it will start itself back up as you are driving and sometimes you will have to hit the key. So far since this has happened I have replaced the fuel tank, fuel pump, and fuel filter. Any ideas where else to look


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[1987 GMC Jimmy]

So you're saying the RPMs will drop way down and then recover, and other times you'll have to start it back up again? You have to shift it into neutral to do this, right? This is completely random? It doesn't do it only when it's warmed up/hot, or there's no subtle pattern to it? There's no bogging down, lurching, or signs that occur a few seconds before to tell you that something's about to happen? There isn't an SES light that pops on a few moments before you start having problems? I had several issues that had me in a similar predicament when I first bought my Jimmy, but the truck would always act up beforehand, usually throw a light, and I'd either have to pull over and restart or drop it into neutral and restart it. Every time it played out like this was something related to computer command control. I'd like more information, but if this is just a one moment it's running great, and the next it's dead type of problem, I highly doubt that it was fuel related to begin with. I would say more like ignition control module, pickup coil, or less likely the remote coil if you don't have codes. If you do have codes, my first suspect would be the TPS sensor, and maybe not even the sensor itself, but a connection problem possibly. If you do have codes, you need to pull them ASAP.

 

[87silveradok20]

So you're saying the RPMs will drop way down and then recover, and other times you'll have to start it back up again? You have to shift it into neutral to do this, right? This is completely random? It doesn't do it only when it's warmed up/hot, or there's no subtle pattern to it? There's no bogging down, lurching, or signs that occur a few seconds before to tell you that something's about to happen? There isn't an SES light that pops on a few moments before you start having problems? I had several issues that had me in a similar predicament when I first bought my Jimmy, but the truck would always act up beforehand, usually throw a light, and I'd either have to pull over and restart or drop it into neutral and restart it. Every time it played out like this was something related to computer command control. I'd like more information, but if this is just a one moment it's running great, and the next it's dead type of problem, I highly doubt that it was fuel related to begin with. I would say more like ignition control module, pickup coil, or less likely the remote coil if you don't have codes. If you do have codes, my first suspect would be the TPS sensor, and maybe not even the sensor itself, but a connection problem possibly. If you do have codes, you need to pull them ASAP.

I haven’t found a pattern tho it seems to do it more when braking or starting but it will die when cruising at a steady rpm too. Sometimes a ses light will pop up but not all of the time. I’ve gotten the low o2 sensor voltage code as the only code to come up. The truck has stubble when you take off but occasionally it won’t do it and will run like a bat out of hell. Most of the time it stumbles tho.


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[1987 GMC Jimmy]

Hmm, okay. So that's a Code 44 you pulled? That signifies a lean condition. Have you checked for vacuum leaks? I'm talking the works here. I'd check to see if the brake booster is holding vacuum with a Mityvac, that the booster check valve works, that your TBI is torqued down properly, that your base gasket isn't bad and leaking vacuum, that your EGR isn't stuck open or otherwise failing to hold vacuum, that your vacuum accumulator ball isn't cracked, that you don't have an evap canister problem that's causing a vacuum leak, and that you don't have any broken/missing lines or anything like that. I'd also check your timing to make sure that it looks good and isn't too retarded. I know you've had this thing for several years, but new leaks can pop up just like that sometimes. If it's starting right back up, I wouldn't rush to suspect a failing ICM, and I'd start with the aforementioned prescription.

 

[Honky Kong jr]

Is the fuel pump shitting the bed and causing the lean condition? Or a bad or failing injector?

 

[1987 GMC Jimmy]

If the fuel pump replacement had no affect on the problem, I'd lean towards no, but if the problem doesn't quickly become apparent, I'd follow up with a fuel pressure test. It wouldn't be surprising to anyone here if a brand new pump was already failing depending on what brand you used. As far as one failing injector goes, I think if that were the case he'd be complaining about it running really nasty and lacking most of its power rather than an almost completely spontaneous shut off. If two were failing completely at the same time, that would be more plausible, which would likely be an electrical issue caused by a poor connection or more likely a failing ICM. He said that it didn't happen only when it was warmed up, so that kind of put the ICM on the back burner for me. The thing that stuck out most to me is when he said that it'll happen when he steps on the brakes, which sounds like a big vacuum leak in the booster.

 

[Honky Kong jr]

Possible internally leaking booster if no external leaks are found.

 

[1987 GMC Jimmy]

Precisely.

 

[87silveradok20]

I actually have only had this truck since June and probably haven’t put 200 miles on it yet. It ran fine and then randomly died one day but fired up and did t do it for another little while. Then it did it again probably 50 miles later. Then the next day (20 miles) it started doing it constantly. I will check for vacuum leaks this weekend and report back. Is there anything else I should watch for?


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[1987 GMC Jimmy]

Well, that whole listing of potential leak points needs to be followed very closely. I'd get a Mityvac and test your booster to make sure it's not leaking because of what you said about the brakes. If you can get your hands on a vacuum gauge after testing the booster, that would help you see where you are to see if it's right or not. You'll need starting fluid to test out the base gasket to see how the idle changes. I'm not suggesting you buy out the store, and I'm not 100% that it's a vacuum leak, but that's where I'd start based on your description of the issue. Just be thorough with it.

 

[87silveradok20]

Well I got my cab of starting fluid out last night and sprayed around. I couldn’t find anything but I did accidentally bump the vacuum line off of the evaporation canister thingy and it didn’t change anything. Idle stayed the same and what not. It should have idled up after this right? Also come to think of it one time I started the truck and it idled really high (like there was a vacuum line off high) but then I shut it off and started it back up and all was fine and nothing of the sort since.


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[Dan Brown]

Have you checked the Idle Air Control Motor. If it's dirty if can cause a high or rough idle. Not sure if being dirty would throw an Idle Air Control Motor code. If there were an electrical system problem with it, then it should throw a code. However, all this ranting may be for naught as you say it happens when you are driving the truck, which is an off idle situation.

 

[87silveradok20]

Have you checked the Idle Air Control Motor. If it's dirty if can cause a high or rough idle. Not sure if being dirty would throw an Idle Air Control Motor code. If there were an electrical system problem with it, then it should throw a code. However, all this ranting may be for naught as you say it happens when you are driving the truck, which is an off idle situation.

It happens at idle as well. If this had a problem would it cause the truck to randomly rev up. Tonight I was backing it in the garage and the pedal went straight to floor on me. My foot was just barely on it to get it over the lip by my garage door.


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[87silveradok20]

Well here’s an update to this thread. I took off the egr valve and checked over all of the vacuum lines again. The problem is still here. It hasn’t thrown any codes the last few days either. I will say that the truck does seem to run better with the egr valve off. I think the old one was sticking open.


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[yevgenievich]

worth checking intermittent ignition related items like ignition switch maybe having a dead spot in it, wires behind the engine shorting due to failed insulation, or aftermarket tach pulling down ignition signal randomly, and also ignition module.

I personally had issues with wires behind the intake braking insulation, aftermarket tach, and failing ignition switch, and fuel pump causing somewhat of similar issues.