Randomly dies

Chuck

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#1
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MAKE: GMC
MODEL: Suburban
YEAR: 1990
MILES: 242000
ENGINE: 5.7L
DESCRIBE ISSUE....My suburban will die for no reason. And there is no pattern or warning when it does. Sometimes it will idle forever if you let it, other times it won't stay running for more than a couple minutes, still others it will start , die and then keep running . It will also die in stop and go traffic, sometimes when I accelerate and other times when I slow down. And again sometimes just sitting at a stop light. Each time it dies though, I can put it in neutral, turn the key and it starts back up again. So far the only time it has stayed running is during highway driving. It did this a few months ago and I changed the fuel filter and that seemed to have fixed the issue. It started doing it again earlier this week and I have changed out the ignition coil and fuel pump (not sending unit) and cleaned the sending unitl connections, and fuel pump relay connections the issue still persists. As I said, there is no warning when it does. It acts like I just turned the key off. any help would be great. Thanks
 
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#2
That is a lot of years and miles. How old is your ignition switch?
 

billr

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#4
I would connect a semi-permanent fuel-pressure gauge with a long hose, ready to observe what FP is doing the moment this beast acts up. The problem could, of course, be electrical (including the ignition switch) and a voltmeter could be used in a similar manner to observe what is happening. I'm focused on the FP because the fuel filter change seemed to have some effect, and because there are many voltages that would have to be checked. Do the FP first because it is a single item to test.
 

Chuck

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#5
I would connect a semi-permanent fuel-pressure gauge with a long hose, ready to observe what FP is doing the moment this beast acts up. The problem could, of course, be electrical (including the ignition switch) and a voltmeter could be used in a similar manner to observe what is happening. I'm focused on the FP because the fuel filter change seemed to have some effect, and because there are many voltages that would have to be checked. Do the FP first because it is a single item to test.
Do I hook it up to the throttle body where the fuel line hooks up?
 

nickb2

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#6
Do I hook it up to the throttle body where the fuel line hooks up?
Where the flexible steel line hooks up to rigid steel line in engine bay is the best location to put a FP gauge "in line" and expect 9-13psi.

To check the dead head pressure, block return line, pressure should jump to about 13-18psi.

When you jump pins A and B of the obd1 connector, do you get codes? You should at least get a code 12 which means obd1 system is ok.

So as bill suggested, that would be a good starting point, but I must say, your symptom sounds alot like an ICM problem, very common on these engines of that era. The module is located inside the dist, many times they will overheat and shut down. You could try repasting the heat sink. But I think an ICM for these trucks is under 30$

Like mobile dan wrote, many years and many miles, so any number of things like the ignition switch, etc may also be the cause. But what we know is pump, ign coil and fuel filter are new. Since you write it sometimes just dies at a stop light, we can maybe rule out a pot hole loosing a connection, but that can't be overruled, so try wiggle testing the engine harness while idling, see if it cuts out. Will give a good indication of where to start looking for an intermittent problem. With problems like this you just need to try anything.

Rock auto has one for 22$. But that is the economy one, I would go a bit higher end like in the standard brand or Delphi for example. They go for about 50$
As I said, there is no warning when it does. It acts like I just turned the key off. any help would be great.
If the fuel pump dies while running, it will usually sputter out, when the ignition control module overheats, dies, it acts exactly as you describe, like the key off all of a sudden. When you go back to start again, it has cooled down enough. Many clients say they have to wait a few minutes, others say just like you, starts right back up. Since the pump is new, I would start focusing on ignition after you have ruled out the fuel is not dropping with the inline pressure gauge tape to wipers to see if that is actually the case while driving.


There are many types of heat sink paste. Some are a gel, some guy's just use dielectric grease which is very adequate also. If I am testing that out, I use that often. Once the OEM paste gets dry and flaky, it doesn't conduct heat well anymore. So if you have some dieltric greae on hand, just pop off the dist cover, unscrew the icm and clean the surfaces well of the dry crud there and apply a thin layer of grease. Test drive to see if the problem goes away. Never know. It has worked for me many times, but most often client comes back a few weeks or months later and I just end up putting in new module in there anyway. It had become a habit of mine to put that in my estimates when I would do a full ignition system overhaul, but I don't see these ICM's much anymore.

So try our suggestions, hope they help and happy holidays.
 
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Chuck

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#7
I will try the FP test after work today. I've done the wiggle test and even used electrical connection cleaner on all that I can see in the engine bay and under the body. Can you send me a diagram of the obd1 connection so I can see were the A and B pins Are? I know the service light doesn't come on until the motor dies, but I think that is just because the ignition is on but the motor isn't running so there is no oil pressure
 

billr

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#8
A & B are the two pins on the right-hand end of the connector upper row. Go to the "manufacturer's codes" in the banner of this (BATauto) site, there is a diagram there.
 

Chuck

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#9
I was able to talk a maintenance guy at work to do a FP check since he just happened to be doing one on a fork lift and he said it held between 10-12 psi all the way up until the motor died. He tested it 3 times with the same result. I then was able the do a jumper test with the obd1 and by the info you guys gave me, it says there are no codes (flash, pause, flash flash).
 

Chuck

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#10
I was able to talk a maintenance guy at work to do a FP check since he just happened to be doing one on a fork lift and he said it held between 10-12 psi all the way up until the motor died. He tested it 3 times with the same result. I then was able the do a jumper test with the obd1 and by the info you guys gave me, it says there are no codes (flash, pause, flash flash).
Where the flexible steel line hooks up to rigid steel line in engine bay is the best location to put a FP gauge "in line" and expect 9-13psi.

To check the dead head pressure, block return line, pressure should jump to about 13-18psi.

When you jump pins A and B of the obd1 connector, do you get codes? You should at least get a code 12 which means obd1 system is ok.

So as bill suggested, that would be a good starting point, but I must say, your symptom sounds alot like an ICM problem, very common on these engines of that era. The module is located inside the dist, many times they will overheat and shut down. You could try repasting the heat sink. But I think an ICM for these trucks is under 30$

Like mobile dan wrote, many years and many miles, so any number of things like the ignition switch, etc may also be the cause. But what we know is pump, ign coil and fuel filter are new. Since you write it sometimes just dies at a stop light, we can maybe rule out a pot hole loosing a connection, but that can't be overruled, so try wiggle testing the engine harness while idling, see if it cuts out. Will give a good indication of where to start looking for an intermittent problem. With problems like this you just need to try anything.

Rock auto has one for 22$. But that is the economy one, I would go a bit higher end like in the standard brand or Delphi for example. They go for about 50$


If the fuel pump dies while running, it will usually sputter out, when the ignition control module overheats, dies, it acts exactly as you describe, like the key off all of a sudden. When you go back to start again, it has cooled down enough. Many clients say they have to wait a few minutes, others say just like you, starts right back up. Since the pump is new, I would start focusing on ignition after you have ruled out the fuel is not dropping with the inline pressure gauge tape to wipers to see if that is actually the case while driving.


There are many types of heat sink paste. Some are a gel, some guy's just use dielectric grease which is very adequate also. If I am testing that out, I use that often. Once the OEM paste gets dry and flaky, it doesn't conduct heat well anymore. So if you have some dieltric greae on hand, just pop off the dist cover, unscrew the icm and clean the surfaces well of the dry crud there and apply a thin layer of grease. Test drive to see if the problem goes away. Never know. It has worked for me many times, but most often client comes back a few weeks or months later and I just end up putting in new module in there anyway. It had become a habit of mine to put that in my estimates when I would do a full ignition system overhaul, but I don't see these ICM's much anymore.

So try our suggestions, hope they help and happy holidays.
just replaced the ICM ran for a little while and still dies.
 

billr

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#11
" it held between 10-12 psi all the way up until the motor died. "

That is a bit vague to me. I would expect the FP to hold up for at least a couple of seconds after the engine dies? Does the pressure drop to near-zero right as the engine stops? Does the FP drop at all, as the engine is running down in rpm? Does the engine "struggle " and die, or just quit cleanly as if the key was turned off?

Obviously, these observations are rather subjective, highly dependent on the skill/experience of the person doing the test. Can you rely on the guy doing it?

If you can get it to die fairly *reliably*, then I would try blasting into the TB with some carb-cleaner as it is dying; see if that helps it keep going a bit.
 

Chuck

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#12
" it held between 10-12 psi all the way up until the motor died. "

That is a bit vague to me. I would expect the FP to hold up for at least a couple of seconds after the engine dies? Does the pressure drop to near-zero right as the engine stops? Does the FP drop at all, as the engine is running down in rpm? Does the engine "struggle " and die, or just quit cleanly as if the key was turned off?

Obviously, these observations are rather subjective, highly dependent on the skill/experience of the person doing the test. Can you rely on the guy doing it?

If you can get it to die fairly *reliably*, then I would try blasting into the TB with some carb-cleaner as it is dying; see if that helps it keep going a bit.
By what he had told me, it held pressure until the motor died. He said it did the same thing. It died like the key had been turned off. And as far as "reliably" dieing, it made it all the way home (roughly 5 miles) with out dieing until I was getting ready to pull into the garage, when it died 3 times within 15 feet. After replacing the ICM it died after roughly 1 to 2 minutes idling.
 

nickb2

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#13
Sucks for the ICM, but as Bill said, does it hold pressure even when engine quits? That is imperative to know. If it drops at moment of quitting, that would be a good indicator of where to look.

Looking at the diagram, the oil pressure switch does control the power to FP, could it be that you have a bad oil pressure switch?Easy way to test that theory is to bypass the oil pressure switch with a jumper. Oil pressure switch should have two terminals. If the engine does not quit on you after you have done that, you have then found the problem to be the oil pressure switch.

After replacing the ICM, you state it died, after 1 to 2 mins idling. What it like that before, or is this a step up in failure time?
 
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Chuck

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#14
Sucks for the ICM, but as Bill said, does it hold pressure even when engine quits? That is imperative to know. If it drops at moment of quitting, that would be a good indicator of where to look.

Looking at the diagram, the oil pressure switch does control the power to FP, could it be that you have a bad oil pressure switch?Easy way to test that theory is to bypass the oil pressure switch with a jumper. Oil pressure switch should have two terminals. If the engine does not quit on you after you have done that, you have then found the problem to be the oil pressure switch.

After replacing the ICM, you state it died, after 1 to 2 mins idling. What it like that before, or is this a step up in failure time?
I didn't think to ask him that yesterday. If he's there today I will find out. Is the oil pressure switch in the same place as the old oil pressure sensor, next to the distributor? I don't know if it a step up because some times it would do that before.
 
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#15
Another version of "jumper diagnostics" would be to run jumper directly from battery to fuel pump relay pump feed pin.
1. Walk to the back of the truck. Can you hear the fuel pump running? Yes?
2. Start the engine. Wait until it quits. Quit? Don't shut off the key, don't slam the door, walk to the back of the truck. Is the pump still running?