2002 Suburban Stalls while driving
June 15th, 2021, 10:23 PM
#11
Just ran into this with TWO Chevy 1500-series vehicles.
BOTH started doing it ONLY at altitude (5k'+) (!!). Same symptom -- at speed, loses power, no response from the accelerator pedal and as you slow it stalls. It will immediately restart and runs perfectly, but will then do it again some time down the road. Appears to be related to the level of heat (yet to have it happen when it's cooler out) -- and in several hours of 100F outdoor temps once returning to lower elevations (~2k'), no problems with EITHER.
Checked the cable to the throttle body (obvious potential problem), nope -- all good. Cycle the ignition off and back on and it restarts. Swapped the fuel pump relay with the DRL one (same number) on the possibility it was bad, no change. Pulled the OnStar fuse (on a lark; possible it was thinking the vehicle was stolen and its worthless now anyway since its AMPS), no change. No code set. Electrical power and dash is normal when it dies (other than obviously the RPM dropping and eventually going to zero when it stalls.)
No good way to check fuel pressure since as soon as you cycle the key it restarts. I SUSPECT the fuel pump (does it have an internal circuit and/or overheat protection?) that may be tripping it under these conditions and when the key is cycled power to it is reset.
I've never seen a MAF or CPS fail without throwing a code -- and I have none.
VERY annoying and, at the wrong time, dangerous! The link to higher altitude is bizarre.
The Express is doing the exact same thing! We are both now down a couple thousand feet and both vehicles are running perfectly...
BOTH started doing it ONLY at altitude (5k'+) (!!). Same symptom -- at speed, loses power, no response from the accelerator pedal and as you slow it stalls. It will immediately restart and runs perfectly, but will then do it again some time down the road. Appears to be related to the level of heat (yet to have it happen when it's cooler out) -- and in several hours of 100F outdoor temps once returning to lower elevations (~2k'), no problems with EITHER.
Checked the cable to the throttle body (obvious potential problem), nope -- all good. Cycle the ignition off and back on and it restarts. Swapped the fuel pump relay with the DRL one (same number) on the possibility it was bad, no change. Pulled the OnStar fuse (on a lark; possible it was thinking the vehicle was stolen and its worthless now anyway since its AMPS), no change. No code set. Electrical power and dash is normal when it dies (other than obviously the RPM dropping and eventually going to zero when it stalls.)
No good way to check fuel pressure since as soon as you cycle the key it restarts. I SUSPECT the fuel pump (does it have an internal circuit and/or overheat protection?) that may be tripping it under these conditions and when the key is cycled power to it is reset.
I've never seen a MAF or CPS fail without throwing a code -- and I have none.
VERY annoying and, at the wrong time, dangerous! The link to higher altitude is bizarre.
The Express is doing the exact same thing! We are both now down a couple thousand feet and both vehicles are running perfectly...
June 16th, 2021, 8:34 AM
#12
Maybe MAP sensor is running on the edge of it's range but not setting a code ?
I've had a MAF running on the edge of it's range, didn't set a code but affected the way my Malibu ran.
I've had a MAF running on the edge of it's range, didn't set a code but affected the way my Malibu ran.
June 16th, 2021, 9:53 AM
#13
I saw someone saying crank sensor, but nope -- the tach is normal and when it acts up it does NOT go to zero. I've seen a CPS failure before and the instant "giveaway" is that the tach goes to zero as soon as it happens. On the Express it misfires before it dies and flashes the check engine light, but on my Suburban it does not; it just has zero throttle response, no flashing check engine, and as you pull over (and thus now the engine is forced to produce "some" power against the torque converter) it dies. But in every case thus far cycling the key off and on has produced an *immediate* restart -- a quick stumble but then normal idle and power is back as usual.
I've never seen a cam sensor fail without throwing a code and there are no codes in the ECU. I've got Torque and an OBDLinkMX but have yet to catch it when it actually happens, and both MAF and MAP (vacuum) look normal while driving. There is no PID exposed for fuel pressure that I can find which sucks big ones because that would *definitively* implicate the fuel pump but it appears that the ECU doesn't have a sensor for that on these vehicles.
The Suburban has the OE fuel pump; it has the relatively common fault that the gauge is off by a fair bit (fuel reading 1/4 is actually EMPTY) but I'm loathe to replace it with a Chineesium one that, if it pukes, will strand me. The Express was bought used so what's been changed on it is unknown but its fuel gauge reads properly.
I'm very interested in the actual design of the fuel pump and exactly what drives and regulates it. If there's a rail sensor at the engine that cycles it then that switch could be involved, but I *suspect* there's a circuit board in the pump that likely either regulates output pressure and/or has thermal and/or overcurrent protection and, if it trips, you get no fuel pressure which would produce this EXACT symptom -- and killing power to it would reset it.
I hate playing "throw parts at this"; it's almost always stupid to go down that road, but given the intermittent nature of the issue and that I can't provoke it "on demand" it's a serious problem trying to find this. The Express is my daughter's and she often uses it for longer-term travel; getting stranded 100 miles from nowhere is NOT cool for obvious reasons, and the threat of an intermittent failure turning into a hard failure is out there.
I've never seen a cam sensor fail without throwing a code and there are no codes in the ECU. I've got Torque and an OBDLinkMX but have yet to catch it when it actually happens, and both MAF and MAP (vacuum) look normal while driving. There is no PID exposed for fuel pressure that I can find which sucks big ones because that would *definitively* implicate the fuel pump but it appears that the ECU doesn't have a sensor for that on these vehicles.
The Suburban has the OE fuel pump; it has the relatively common fault that the gauge is off by a fair bit (fuel reading 1/4 is actually EMPTY) but I'm loathe to replace it with a Chineesium one that, if it pukes, will strand me. The Express was bought used so what's been changed on it is unknown but its fuel gauge reads properly.
I'm very interested in the actual design of the fuel pump and exactly what drives and regulates it. If there's a rail sensor at the engine that cycles it then that switch could be involved, but I *suspect* there's a circuit board in the pump that likely either regulates output pressure and/or has thermal and/or overcurrent protection and, if it trips, you get no fuel pressure which would produce this EXACT symptom -- and killing power to it would reset it.
I hate playing "throw parts at this"; it's almost always stupid to go down that road, but given the intermittent nature of the issue and that I can't provoke it "on demand" it's a serious problem trying to find this. The Express is my daughter's and she often uses it for longer-term travel; getting stranded 100 miles from nowhere is NOT cool for obvious reasons, and the threat of an intermittent failure turning into a hard failure is out there.
June 17th, 2021, 6:56 AM
#14
I'm on several other Chevy groups and one common issue with Traverse and Malibu's is fuse box failures. I bet the same boxes are common across the GM's.
They heat up and open up / fail. Lots of reports on stop then the start and go again with being intermittent and no codes.
I'd check the undersides of the main fuse box for signs of heat build up. Loss of power to the fuel pump or PCM will not set any codes either.
They heat up and open up / fail. Lots of reports on stop then the start and go again with being intermittent and no codes.
I'd check the undersides of the main fuse box for signs of heat build up. Loss of power to the fuel pump or PCM will not set any codes either.
June 17th, 2021, 9:32 AM
#15
This problem is quite-specific and as a result doesn't point at that sort of failure.
I've put north of 3,000 miles on the truck in the last week (as has my daughter with hers) and the shutdowns only happen under the following conditions:
1. At altitude, over 5,000', where material changes in altitude have happened during the current drive cycle (since the truck was started.)
2. Hot outside (>80-85F)
I just got home last night -- from KC to NE TN and the previous day all the way from Colorado Springs. 12 hours continual operation at highway speeds, BUT all downhill, leaving the 5k' zone in Colorado Springs. 100F outside for basically the entire way across Kansas, 80mph, A/C blazing of course, no problems. Then home, same deal except a bit slower since the 75mph speed limits disappear when you reach Illinois, again -- no problems.
My daughter, same deal. She went south with hers, but once out of Taos and into NE NM and then through TX, no problems. And it was hotter than hell through Texas, so it's not heat.
When it dies it is not a "hard" cut-off in either case; it acts like there is no fuel pressure. There's no PID for it, so I can't prove it without a gauge hooked up to the test port, and now I'm back in the lower elevations so I'm not sure I can provoke it again at all. There's no heat evident on the fuel pump relay pins and the expected indication of a crank position sensor (which would cause the ECU to think the engine has stopped and shut the fuel pump off) -- the tach going to zero -- does not occur. The engine clearly has ignition as it IS running and has very little (but not zero) throttle response until it stalls.
In addition in every instance thus far as key off produces an immediate restart, so whatever it is looks like a "trip" of some sort that is electronic and cleared by a power cycle.
I'm quite curious as to what sort of internal sensors are in that fuel pump's control system (internal to the pump, since on this year my understanding is that there's no separate module; the relay is a direct connection to pump power itself) and that the pump ITSELF regulates fuel pressure. If the PCM dropped the relay intentionally I'd expect a code for something, and the PCM is not losing power or I'd lose the dash gauges -- which does not happen. The relay ITSELF was swapped as that was my first suspicion but that's not the problem as it did not resolve it.
I'm going to check the purge valve today since I'm home where I have tools; I'm curious if a significant pressure differential (e.g. the vent is blocked or the valve is malfunctioning in some way) could cause a pressure differential in the tank with altitude changes that doesn't set a code but *does* freak the pump out and cause it to shut down.
I've put north of 3,000 miles on the truck in the last week (as has my daughter with hers) and the shutdowns only happen under the following conditions:
1. At altitude, over 5,000', where material changes in altitude have happened during the current drive cycle (since the truck was started.)
2. Hot outside (>80-85F)
I just got home last night -- from KC to NE TN and the previous day all the way from Colorado Springs. 12 hours continual operation at highway speeds, BUT all downhill, leaving the 5k' zone in Colorado Springs. 100F outside for basically the entire way across Kansas, 80mph, A/C blazing of course, no problems. Then home, same deal except a bit slower since the 75mph speed limits disappear when you reach Illinois, again -- no problems.
My daughter, same deal. She went south with hers, but once out of Taos and into NE NM and then through TX, no problems. And it was hotter than hell through Texas, so it's not heat.
When it dies it is not a "hard" cut-off in either case; it acts like there is no fuel pressure. There's no PID for it, so I can't prove it without a gauge hooked up to the test port, and now I'm back in the lower elevations so I'm not sure I can provoke it again at all. There's no heat evident on the fuel pump relay pins and the expected indication of a crank position sensor (which would cause the ECU to think the engine has stopped and shut the fuel pump off) -- the tach going to zero -- does not occur. The engine clearly has ignition as it IS running and has very little (but not zero) throttle response until it stalls.
In addition in every instance thus far as key off produces an immediate restart, so whatever it is looks like a "trip" of some sort that is electronic and cleared by a power cycle.
I'm quite curious as to what sort of internal sensors are in that fuel pump's control system (internal to the pump, since on this year my understanding is that there's no separate module; the relay is a direct connection to pump power itself) and that the pump ITSELF regulates fuel pressure. If the PCM dropped the relay intentionally I'd expect a code for something, and the PCM is not losing power or I'd lose the dash gauges -- which does not happen. The relay ITSELF was swapped as that was my first suspicion but that's not the problem as it did not resolve it.
I'm going to check the purge valve today since I'm home where I have tools; I'm curious if a significant pressure differential (e.g. the vent is blocked or the valve is malfunctioning in some way) could cause a pressure differential in the tank with altitude changes that doesn't set a code but *does* freak the pump out and cause it to shut down.
June 17th, 2021, 2:10 PM
#16
Update on troubleshooting in the event someone has further info....
Considered the possibility the cannister and manifold purge valves were malfunctioning, since that would cause a lean-out condition if they failed the wrong way (cannister purge open, manifold purge open) that might be enough to not be able to be overcome with fuel trim at altitude. I was seeing long term trims moderately positive at altitude -- well below the warning threshold, but definitely not zero. As altitude decreased it came down.
The manifold purge valve tests good both off the car static (no flow) and for flow both with pressure and vacuum on the cannister port when power is applied and removed manually. The cannister vent valve tests good too, EXCEPT that if there is pressure it will not open until it goes away.
The cannister vent valve connector has +12V on it with key on, BUT when the valve is plugged in I do not hear it click closed. I DO have +12V from the hot side of the plug to chassis, however, so I know the chassis ground is good (the braid strap from the engine also looks to be in good condition as well.)
I'm tempted to replace the cannister vent valve as its reasonably cheap, but I've got a problem with trying to reproduce this in my local area, since it only happens at altitude and I don't think I can get it high and hot enough here in NE TN to make it happen. But that or the fuel pump appear to be the only possible indications, and I SHOULD be able to see a difference in the fuel trims if the valve is bad.
Considered the possibility the cannister and manifold purge valves were malfunctioning, since that would cause a lean-out condition if they failed the wrong way (cannister purge open, manifold purge open) that might be enough to not be able to be overcome with fuel trim at altitude. I was seeing long term trims moderately positive at altitude -- well below the warning threshold, but definitely not zero. As altitude decreased it came down.
The manifold purge valve tests good both off the car static (no flow) and for flow both with pressure and vacuum on the cannister port when power is applied and removed manually. The cannister vent valve tests good too, EXCEPT that if there is pressure it will not open until it goes away.
The cannister vent valve connector has +12V on it with key on, BUT when the valve is plugged in I do not hear it click closed. I DO have +12V from the hot side of the plug to chassis, however, so I know the chassis ground is good (the braid strap from the engine also looks to be in good condition as well.)
I'm tempted to replace the cannister vent valve as its reasonably cheap, but I've got a problem with trying to reproduce this in my local area, since it only happens at altitude and I don't think I can get it high and hot enough here in NE TN to make it happen. But that or the fuel pump appear to be the only possible indications, and I SHOULD be able to see a difference in the fuel trims if the valve is bad.
June 17th, 2021, 3:28 PM
#17
Aha..... I may have it here.
On a lark bought a cannister vent solenoid. THIS ONE will open if power is removed on the bench whether there is vacuum or pressure on the port. The OLD one will NOT open if there is pressure and you drop control voltage.
So here's the scenario I suspect is going on. As elevation goes up with the valve commanded closed tank pressure builds relative to outside ambient air. The PCM commands it open but nothing happens; it does not know since there is no sense line, only power. If the PCM then opens the vapor cannister purge to the manifold you get a slug of air from the tank down the intake beyond the MAF which wildly leans the mixture and, given that you're at altitude where the air is thin to begin with.... you're done. This also explains why a restart always works; when you shut the key off the PCM drops control voltage to the valve into the manifold, which closes it.
It's a decent theory and an EXACT match on the behavior of the old valve, which differs from the new one, that might well fit the facts. We'll see.
On a lark bought a cannister vent solenoid. THIS ONE will open if power is removed on the bench whether there is vacuum or pressure on the port. The OLD one will NOT open if there is pressure and you drop control voltage.
So here's the scenario I suspect is going on. As elevation goes up with the valve commanded closed tank pressure builds relative to outside ambient air. The PCM commands it open but nothing happens; it does not know since there is no sense line, only power. If the PCM then opens the vapor cannister purge to the manifold you get a slug of air from the tank down the intake beyond the MAF which wildly leans the mixture and, given that you're at altitude where the air is thin to begin with.... you're done. This also explains why a restart always works; when you shut the key off the PCM drops control voltage to the valve into the manifold, which closes it.
It's a decent theory and an EXACT match on the behavior of the old valve, which differs from the new one, that might well fit the facts. We'll see.
The following users liked this post:
repairman54 (June 18th, 2021)
June 19th, 2021, 4:16 PM
#18
So new valve installed and drove it up to 6,500' altitude, no problems. But -- it wasn't over 80F, which I can't do anything about and which makes the test questionable. The long-term fuel trims did change with that new valve installed to some degree -- not a lot, but noticeable (positive deviation from what they were.) I also checked the fuel pressure, which I can't do while driving as the hose I have is nowhere near long enough to snake it somewhere useful; just over 50psi with the key on but engine off, right around 40-45psi at idle and spikes higher (mid 50s) when I blip the throttle good. That implies that the pump itself is delivering fuel at reasonable volume and the regulator is good.
The bodies of the relays that are energized when the truck is running are all equally warm (A/C, DRL and fuel pump) implying that there isn't a problem with the wiring under the relay block, and none of the terminals on the relays are burnt, so that isn't implicated either.
When I went to remove the gauge I pulled the relay and cranked to relieve the pressure so it wouldn't spray gas all over the place and got the exact behavior I get when it acts up. So I'm back to....
1. The pump itself shut down even though the drive to it is present (relay is closed)
OR
2. The PCM (or another module that can) commanded it off.
So I'm back to "under what conditions will the pump shut down that are cleared by a power-cycle (key off and back on)", and does the pump have logic in it that can cause it to do that on its own (e.g. not thermally protected which will automatically reset, but which would reset only on a power cycle.)
Does the pump itself have circuitry in it that will shut it down under what it determines to be "unacceptable" conditions and, if so, what are they? I'm loathe to replace a perfectly-good pump if that's not where the problem lies!
The bodies of the relays that are energized when the truck is running are all equally warm (A/C, DRL and fuel pump) implying that there isn't a problem with the wiring under the relay block, and none of the terminals on the relays are burnt, so that isn't implicated either.
When I went to remove the gauge I pulled the relay and cranked to relieve the pressure so it wouldn't spray gas all over the place and got the exact behavior I get when it acts up. So I'm back to....
1. The pump itself shut down even though the drive to it is present (relay is closed)
OR
2. The PCM (or another module that can) commanded it off.
So I'm back to "under what conditions will the pump shut down that are cleared by a power-cycle (key off and back on)", and does the pump have logic in it that can cause it to do that on its own (e.g. not thermally protected which will automatically reset, but which would reset only on a power cycle.)
Does the pump itself have circuitry in it that will shut it down under what it determines to be "unacceptable" conditions and, if so, what are they? I'm loathe to replace a perfectly-good pump if that's not where the problem lies!
June 20th, 2021, 6:34 AM
#19
Pump itself is just a motor driven pump. No circuitry in it. Diagram will show it's circuitry. I use alldatadiy.com online manuals for my ''fleet'' of vehicles.
Not sure on a '02 but my '11 has a fuel pump control module.
I had a '88 Taurus that after being driven awhile the fuel pump would heat up and slowly loose fuel pressure. Park it for a while or stop and put fresh cold gas in it and it would go again just fine. Only on hot days, at night when cooler out it did not act up. No fuel control modules in that car, pump just relay activated by PCM.
Made me crazy until I realized that stopping and putting fresh cool gas in the tank cooled the pump down so it kept running on a hot day.
Only saw it after running it on a hot day and letting it idle at the house with pressure gauge on it and watching pressure slowly drop off until it stalled out. Pump change fixed it, like you I didn't want to drop the tank to change the pump without being sure.
Not sure on a '02 but my '11 has a fuel pump control module.
I had a '88 Taurus that after being driven awhile the fuel pump would heat up and slowly loose fuel pressure. Park it for a while or stop and put fresh cold gas in it and it would go again just fine. Only on hot days, at night when cooler out it did not act up. No fuel control modules in that car, pump just relay activated by PCM.
Made me crazy until I realized that stopping and putting fresh cool gas in the tank cooled the pump down so it kept running on a hot day.
Only saw it after running it on a hot day and letting it idle at the house with pressure gauge on it and watching pressure slowly drop off until it stalled out. Pump change fixed it, like you I didn't want to drop the tank to change the pump without being sure.
June 20th, 2021, 7:41 AM
#20
I'm pretty sure there's no fuel control module in these trucks; I can't find a sensor on the rail anywhere (just a mechanical regulator that takes manifold vacuum as a control and from what I can see it appears to be working as I can see the rail pressure change when I blip the throttle, which is what you'd expect from it.)
What gets me in this case is the immediate restart when you key off/on. You don't have to wait for things to cool down, which would make sense, or putting cool fuel in it (ditto.) Indeed when it occurred in Denver traffic I keyed off/on while still moving as I was trapped in a construction zone with no shoulder to pull off the road (!!) and it lit right back up. I'd be highly suspicious of the crank sensor and the PCM dropping control voltage except that when it happens the tach continues to read; the gearbox is in overrun but it still has line pressure as the engine is turning and it has power an thus stays "in gear." Every time I've seen a crank sensor die the tach has gone to zero immediately.
One thing I did note is that the AIT (intake temperature) gets REALLY warm on hot days at high altitudes. I've seen 150F (!!!) on Torque which is wildly elevated; even coming back across Kansas in 100F ambient temps AIT was only running around 120F. That's likely due to the thinner air and thus less cooling of everything under the hood including those nice, toasty exhaust manifolds and collectors down there, and I assume that also means the returned fuel is going to be nasty-hot as well.
What gets me in this case is the immediate restart when you key off/on. You don't have to wait for things to cool down, which would make sense, or putting cool fuel in it (ditto.) Indeed when it occurred in Denver traffic I keyed off/on while still moving as I was trapped in a construction zone with no shoulder to pull off the road (!!) and it lit right back up. I'd be highly suspicious of the crank sensor and the PCM dropping control voltage except that when it happens the tach continues to read; the gearbox is in overrun but it still has line pressure as the engine is turning and it has power an thus stays "in gear." Every time I've seen a crank sensor die the tach has gone to zero immediately.
One thing I did note is that the AIT (intake temperature) gets REALLY warm on hot days at high altitudes. I've seen 150F (!!!) on Torque which is wildly elevated; even coming back across Kansas in 100F ambient temps AIT was only running around 120F. That's likely due to the thinner air and thus less cooling of everything under the hood including those nice, toasty exhaust manifolds and collectors down there, and I assume that also means the returned fuel is going to be nasty-hot as well.