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Discussion Starter · #21 ·
More than likely you are having an electrical problem.
What is condition of the WIF and fuel heater wires and connectors at the FFM.
Look for missing insulation where they enter the FFM.
Try unplugging them, will run fine and not affect operation.
The PCM can turn off stuff if there is a short, it has solid state circuit breakers.
It will automatically reset, but I would not let it go on doing this for long.
As a test - unplug the BARO, IAT, MAP, and ECT sensors and see if it still dies.
I do not know what condition those 2 connectors are in. I will try to look at it in the morning as well as unplug those sensors. Also someone I don't remember who said a possible ignition switch. Do you think that is possible?
 

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Discussion Starter · #22 ·
More than likely you are having an electrical problem.
What is condition of the WIF and fuel heater wires and connectors at the FFM.
Look for missing insulation where they enter the FFM.
Try unplugging them, will run fine and not affect operation.
The PCM can turn off stuff if there is a short, it has solid state circuit breakers.
It will automatically reset, but I would not let it go on doing this for long.
As a test - unplug the BARO, IAT, MAP, and ECT sensors and see if it still dies.
I unplugged the sensors and no change. I inspected the wiring to the FFM and did not see any bare wiring. I unplugged them just in case i missed something and still no change. Could the fuel shut off solenoid be getting weak? I have seen in rare occasions on the reefers that I work on as it heats up It causes the solenoid to act goofy. I've read about people gutting them for no start problems but never for this type of problem.
 

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Could be the ign. sw.
Does anything else quit working when the engine dies?
Could be the FSO.
Do you have an automatic transmission? A bad shift solenoid can cause your problem.
Testing various circuits for power before and after it dies will narrow down the search.
 

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Discussion Starter · #24 ·
Could be the ign. sw.
Does anything else quit working when the engine dies?
Could be the FSO.
Do you have an automatic transmission? A bad shift solenoid can cause your problem.
Testing various circuits for power before and after it dies will narrow down the search.
No I do think anything else stops working that is a good thought i didn't think of. Yes it is a automatic. When I get back to the truck I will check and see if everything else still works like normal and will try gutting the fuel solenoid and see if that changes anything. Would a bad shift solenoid affect it in park?
 

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According to GM reference material the quad driver which includes the PMD drive command is on the same circuit as the EGR vent solenoid, the EGR control solenoid, the turbocharger vacuum control solenoid and the transmission 1-2 shift solenoid.
If any of these solenoids, shorts or shorts intermittently, it will trip the quad driver and shut down all three in the same companion circuit. Since the thermal protection of a quad driver is much the same as a circuit breaker, it will reset and turn on again.

You may or may not have EGR, yes or no?
But you do have the turbo solenoid.
1-2 shift solenoid is ON in all gears, including park, except 2nd and 3rd.
You can unplug the main transmission connector to test.
Truck will still run but will only have 2nd gear, (both shift solenoids OFF).
 
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Discussion Starter · #26 ·
According to GM reference material the quad driver which includes the PMD drive command is on the same circuit as the EGR vent solenoid, the EGR control solenoid, the turbocharger vacuum control solenoid and the transmission 1-2 shift solenoid.
If any of these solenoids, shorts or shorts intermittently, it will trip the quad driver and shut down all three in the same companion circuit. Since the thermal protection of a quad driver is much the same as a circuit breaker, it will reset and turn on again.

You may or may not have EGR, yes or no?
But you do have the turbo solenoid.
1-2 shift solenoid is ON in all gears, including park, except 2nd and 3rd.
You can unplug the main transmission connector to test.
Truck will still run but will only have 2nd gear, (both shift solenoids OFF).
I do not have egr so that rules out one more thing. I will try unplugging the wastegate solenoid and trans plug and see if it makes a difference.

I do truly appreciate all the help you guys have been so far. Hopefully with you guys telling me what to do I can get this thing figured out.
 

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Discussion Starter · #27 ·
Ok tried running with wastegate solenoid unplugged and no change. I cannot get under the truck to get the angle i need to reach the trans connector. Looking at some wiring diagrams if i where to unplug the trans fuse in the dash would this do the same as unplugging it for your test? It looks like the shift solenoids get power from that fuse then the PCM does its thing to make them do there thing when needed? Am I just wasting my time going down this avenue?
 

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The PCM needs to be disconnected from the shift solenoids.
Removing the 12v. will not change the fact there may be a shorted solenoid.
After running it with those sensors unplugged, do you have any codes stored?
 

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Discussion Starter · #29 ·
Ok I will try again tomorrow to get that plug out. Was hoping that it would be as easy as pulling a fuse. Every thing but the waste gate solenoid unplugged threw a code. I did not look to see if it stored them. And just to make sure I am trying to get the right plug the one i am looking for is towards the rear of the trans on the drivers side correct blocked pretty much by the driveline?
 

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There are 2 flat spots on the 4L80 conn.
Squeeze those towards each other and wiggle out to release the conn.
Google "4L80e connector" and you will see.
As long as codes are showing up the PCM should be OK.
Did you do anything with the FSO?
Problems like yours are a PITA and I have found that the best way to find the problem
is to keep eliminating what isn't the problem based on experience.
 

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Discussion Starter · #31 ·
There are 2 flat spots on the 4L80 conn.
Squeeze those towards each other and wiggle out to release the conn.
Google "4L80e connector" and you will see.
As long as codes are showing up the PCM should be OK.
Did you do anything with the FSO?
Problems like yours are a PITA and I have found that the best way to find the problem
is to keep eliminating what isn't the problem based on experience.
Ok I was going after the correct plug. I just have to figure out how to get up there to get it unplugged. I did try gutting the fso but I couldn't figure out how to get the Plunger out. Does it have to be cut off? I hate electrical problems but I agree eliminate enough things and you'll find the problem. Im more familiar with gas engines the these. The diesels I work with at work are way simpler then this thing is.
 

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Discussion Starter · #33 ·
Ok I got the FSO gutted and did not change anything other then create a fuel leak. I think I tore the oring when I pulled it out. I have not been able to get the trans plug unplugged yet. I can't my arms to bend the way I need to with laying on my back and having back issues doesnt help.
 

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Discussion Starter · #34 ·
Thank you I did read that post before starting on it this morning. Since I am having problems getting under the truck and to the plug would it be possible to just de-pin the wires I need at the ECM? I know thats alot more work but right now that is my only option with my psychical difficulties
 

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Sure can. I'll post some schematics.
 

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PCM pinouts
 

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While you are into the PCM. Be sure to check for 12v power from the ign switch at Pin A1 pink wire. Might want to start the engine and wait till it stalls. Then check before turning the ign switch to off.
 

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Discussion Starter · #40 ·
While you are into the PCM. Be sure to check for 12v power from the ign switch at Pin A1 pink wire. Might want to start the engine and wait till it stalls. Then check before turning the ign switch to off.
Just got done checking that. When it stalls I still have 12v. Havent gotten to pulling pins yet. I have to find my release tool.
 
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