Please Help! 98 Chevy intermittent stalling mystery

Maintenance/Repairs
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1

Hi all- I have a 98 Chevy C2500 pickup (5.7L Vortec 350) that I am having a real frustrating time with. A few weeks ago, I noticed that very occasionally, after the vehicle was warm, I would see a sudden full RPM dip to 0 while driving down the highway, but then the vehicle would return to normal operation. It would happen quickly and would not be any sort of aggressive sputtering.

Then it got to the point where I would have been driving my 10 minute commute on the highway, and then when I took an exit and started driving at 20 mph or so, the truck would completely die, or stall, not sure which one to call it. I would have dash lights, but I would have to quickly shift to N and turn the key off and on and it will fire right back up.

It doesn’t sputter then stall, it just dies and then starts right back up. A few times though it was a bit hard to start it back up. I’ve read that could indicate a failing fuel pump. I can hear the pump loud and clear though so I know it is working at least most of the time.

It seems to idle very low, and my oil pressure also gets down to around 10 psi at idle when the engine is really warm.

It rarely will die at idle, it seems to mostly happen when driving at around 20 mph.

I will stress that it really doesn’t stall DURING acceleration, but instead AFTER I have accelerated and then slowed back down.

I have changed spark plugs and wires, cleaned throttle body and MAF, and cleaned the IAC valve. I also replaced the fuel filter.

I have read stalling problems with these engines could be EGR related, TPS, IAC, ICM, etc.

The truck is in a shop now, and they called me today and said they drove it for a long time, probably 30 miles or so on the highway, and they could not get it to stall. They say it ran perfect. This is just an annoying coincidence- the other night it ran good for me and didnt stall, but It has stalled on me almost every day multiple times in the last week. I told them I will come in and drive it with someone and hopefully get it to stall so they can see.

Anyways, does anyone have an idea what could be causing such an incredibly intermittent stalling issue like this? It doesn’t seem to be fuel, because it doesn’t sputter before or after it stalls. Should I just start replacing easy parts like the ICM and TPS myself? Could it still be my fuel pump? What could be getting hot and working differently than when cold? Could it just be my battery is bad? It is a bit old. Could that be distributor cap and rotor? I didn’t replace those yet (just plugs and wires).

Could it be the fuel pump relay gets hot and somehow stops making a connection?

Any help would be greatly appreciated! I don’t have the money right now to chase this problem endlessly with an auto shop…

Ben

2

Check the wiring to the fuel pump. I had a '97 Blazer that stalled and the problem was wore insulation, resulting in intermittent shorting out and stalling.

Not saying for sure this is it, but it’s relatively inexpensive and somewhat simple to check.

3

I really feel for you. That kind of problem is annoying and hard to fix. These trucks are prone to fuel pump failures and that may cause a stall and restart. It might make sense to just change the fuel pump relay, they are cheap.

Failing ignition parts can cause it, too. I think these still only have a DEI distrubutor and no external spark control so it could be the ignition module. Likely cheaper to replace than a fuel pump.

How many miles on it?

4

I would suspect the Crankshaft Position Sensor.

https://www.rockauto.com/en/moreinfo.php?pk=926391&cc=1303401&jsn=455

If you see the tach drop to 0 RPM’s and the engine shuts off, it means the tach lost its signal from the crank sensor.

Tester

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5

Thanks for the reply!

The truck has 108k miles. The ICM will be high on my list.

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Thanks for the help. Sounds like that would be a really good thing to try first if I start throwing parts at it.

Ben

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Thanks for the input. Is checking that wiring a tricky job or no? Where would I start?

Ben

8

I thought you said the pump was running? Therefore not the fuel pump. You didn’t mention the crank sensor but really, the best you can do is wait for it to get worse. Shutting off momentarily and back on again when you flip the switch, certainly does indicate some kind of an electrical issue. Check all grounds and connections. Fuse connections, especially for the computer. Computer connections, and so on as a start. I suppose coming off of highway speed to slower speed could be a dirty throttle body or IAC but don’t think that would cause your other symptoms. so you could have two different issues.

Do general maintenance then wait for it to get worse is my advice. I spent months trying to find the cause of stalling and finally gave up. I could fill the rest of the page with everything I did including the ignition switch. I’d take it out at night with a fuel pressure tester taped to the windshield and a test light on the fuel pump circuit, and after 7 miles it would stall. No codes, etc. and start right up. Even had the wires all changed from the pump to the computer and just gave up, but good luck.

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Hey thanks so much for the reply. I guess it is just an unfortunate situation. Its too bad that it has started to feel so dangerous to drive (losing power steering and braking while in traffic) or I would have less of a problem driving it till it got worse… Oh well! I will check my connections and maybe throw a couple hundred bucks in small parts at it to begin with. Thanks again.

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Unfortunately, I didn’t find it so I can’t tell you how difficult it would be to find. I had my mechanic look into the problem, he saw a spark, and was able to easily see the worn insulation. The spark helped focus the search. It was on an exposed portion of the wiring that was touching another piece in the engine compartment that vibrated. I guess 20 years of the minute amount of rubbing simply wore the insulation off.

If it was me looking for such a thing, I would open the hood with the engine off and note where wiring is not protected by any covering or harness or that might have greater exposure to heat. I would then turn on the engine and note what portions may be subject to rubbing or vibration; if you have lived a good and pure life, you may get lucky and see a spark! I’d then turn off the engine and inspect the wiring in those locations. If it has been sparking, you may see discolored/burnt spots. I’d also try to get a wiring diagram, find the wiring for the possible causes and inspect the individual wires.

If you don’t find anything, at least you have done your best to find a simple and less expensive cause. I know I’d feel lousy if I threw a couple hundred dollars of parts at a fix only to find that it was something I could have found had I inspected it.

11

Sometimes you can even HEAR the spark, as it escapes past the bad insulation and finds a path to ground

Kind of sounds like somebody clicking a ball point pen

It also helps if it’s dark outside. Sometimes that makes it easier to see misfires due to bad plug wires

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12

Have you checked fuel pressure? A weak fuel pump can run, but not deliver optimal fuel pressure. I wouldn’t replace a fuel pump without checking pressure first.
Along those lines, when was the fuel filter last replaced?

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13

My guess is the same as Mustang’s, faulty ignition module. But it’s just a guess. Could be the fuel pump or the crank position sensor among other things. If you can get it to stall and not start, that would be a good time to check for spark at a spark plug during cranking. If you do that and find the spark is ok but it still won’t start, ask your shop if they can fix you up with a fuel pressure gauge located where you can see it as you drive. Next time this happens look at the gauge. If it is registering close to zero, you know you have a fuel pressure problem. That doesn’t 100% mean the problem is the pump — the pump won’t work if the ECM thinks the engine isn’t turning – but the guess at that point would still be the pump.

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When I was trying to figure out my stalling problems, I got a coil with the ignition module from a junk yard for about $25. Should be no problem getting a used one to try. That wasn’t it for me but was a cheap try.

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Hi all- this is way late but I thought I would post the fix- it was the crankshaft pos sensor. For some reason when I checked for codes at autozone (twice) I saw nothing, but once I brought it to a shop they saw it was throwing the CPS code. He put a new one in and problem was solved.

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16

Pickup coil under distributor. Mark the firewall with where the rotor points, so you can get as close as possible with the next one. Then pull the distributor out and replace with a known good working one. Problem solved.

17

Had same problem with 98 C1500 with 4.3L. Resolved problem by removing and cleaning discolored maxi fuses in under hood fuse box. Good idea to clean all. Start by disconnecting negative battery terminal from battery. Remove and clean or replace fuses and clean fuse terminals with contact cleaner an small brush.

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For crying out loud , if you had read thread you would have seen that the person who stated this over 2 years ago posted the the result and what was done to fix it.

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Yeah, you have to be quick on the draw here. You just can’t wait a couple years to help or you’re late to the party. Not to mention skipping all the other responses. Kinda like the guy waking up in the middle of a conversation.