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Discussion Starter #1
tested plunger with 12v out of truck and see work. Put multimeter to power side and got 10volts. Tried plunger with key on exposed and no work.
Truck has issues with starting.....could be PMD ....could be something else. Put someone elses PMD last known good and got truck to run with solenoid half in with external supplied 12v hearing the click and started and ran great 2-3 times. Tried connecting back up to harness and worked fine. Then screwed in all the way hooked up. Came back to try start an hour later and ....no start again. Thinking eliminate solenoid shutoff may be good idea?
 

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you just unplug it, unscrew it, remove the snap ring and the plunger comes out. Put it back togather and run it. Mine has not had a plunger in a long time as I thought that may have been my problem too.

turned out to be something else but I just left it disassembled.
 

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Do you remember what it turned out to be? guessing low voltage at plunger showing something else 10volts?
 

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you just unplug it, unscrew it, remove the snap ring and the plunger comes out. Put it back togather and run it. Mine has not had a plunger in a long time as I thought that may have been my problem too.

turned out to be something else but I just left it disassembled.
X2 same here no plunger in mine either & it ain't going back in while I own it...

I think them crooks GM only left the solenoid in there to have another way for something cheap to fail so they could charge us $2K for an IP replacement consistent with the PMD failures.
 

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Solenoid serves no purpose. Gut it and forget it. When you shut power off to the pump it no longer pumps fuel, so the shut-off solenoid is just another component that can put your truck to the side of the road dead. Unfortunately it needs to remain plugged in so the computer can "see it". The ECM provides a ground path and when it does not see ignition voltage it throws a ESO Solenoid Circuit Fault. Quite sure you could put a small resister between the two wires and fool the computer if you so desired. Just think of all the fuel you'll be saving by not having to supply voltage to defunct solenoid all the time.
 

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Solenoid serves no purpose. Gut it and forget it. When you shut power off to the pump it no longer pumps fuel, so the shut-off solenoid is just another component that can put your truck to the side of the road dead. Unfortunately it needs to remain plugged in so the computer can "see it". The ECM provides a ground path and when it does not see ignition voltage it throws a ESO Solenoid Circuit Fault. Quite sure you could put a small resister between the two wires and fool the computer if you so desired. Just think of all the fuel you'll be saving by not having to supply voltage to defunct solenoid all the time.
So what's the purpose to it ? It don't make sence that there would be a part added that serves %100 no purpose

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So what's the purpose to it ? It don't make sence that there would be a part added that serves %100 no purpose
There are lots of parts on vehicles that serve no purpose. Suppose it's just there to keep the engineers busy. I am sure several people here will tell you why they think it's there but I can assure you it will work just fine without it.

Kinda like muffler bearings. Most vehicles work just fine without them.
 

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So, you mean that, once you've pulled out the plunger, the fuel shut off solenoid can remain as is on the IP, even disconnected, and that should not create any issue?

How do you shut off the engine then?
 

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Solenoid serves no purpose. Gut it and forget it. When you shut power off to the pump it no longer pumps fuel, so the shut-off solenoid is just another component that can put your truck to the side of the road dead. Unfortunately it needs to remain plugged in so the computer can "see it". The ECM provides a ground path and when it does not see ignition voltage it throws a ESO Solenoid Circuit Fault. Quite sure you could put a small resister between the two wires and fool the computer if you so desired. Just think of all the fuel you'll be saving by not having to supply voltage to defunct solenoid all the time.
So, you mean that, once you've pulled out the plunger, the fuel shut off solenoid can remain as is on the IP, even disconnected, and that should not create any issue?

How do you shut off the engine then?
I had no idea about this, I figured this solenoids purpose was to shut off the truck.
 

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Could be the 'Engine Shutoff Solenoid's real function is misunderstood.

Engine Shutoff Solenoid
"Circuit Description: When the ignition switch is in the "OFF" position, the Engine Shutoff Solenoid is in the "NO Fuel" position. By providing a ground path, the PCM energizes the engine shutoff solenoid which then allows fuel to pass into the injection pump."

Also found elsewhere in the GM service manual.
"When not activated by the PCM, the engine shutoff solenoid blocks fuel flow from entering the transfer pump inside the injection pump and stops engine operation."

Thats practically all thats mentioned about the Engine Shutoff Solenoid in the service manual... Much like the fuel solenoid, PMD, or OS, the engine shutoff solenoid wasn't included in the ON-VEHICLE SERVICE section that included virtually everything else.

Although designated as the "engine shutoff solenoid", it might best be described as the PCM's "Emergency Engine Shutoff Solenoid."
Try to think of it more as the PCM's primary panic button instead of just an redundant 'ON-OFF" switch...
The other "fuel solenoid" is activated by the Pump Mounted Driver that is controlled by the PCM.
When the ignition is switch'd "OFF", the PMD cant communicate with the PCM thus "engine shuts off" as others have confirmed by removing the Engine Shutoff Solenoid's plunger yet engine shuts off under NORMAL operating conditions.....

I stress NORMAL operating conditions because the PCM has a several other operating modes besides the more common "Normal" (open) and "Diagnostic" modes.
"Fuel is delivered under one of several conditions called "modes." All modes are controlled by the PCM."
A couple lesser known "modes" of the PCM include "Starting Mode" and an even lesser known "Fuel Cutoff Mode" that are only briefly mentioned in the manual elsewhere and not in the Control Module System section as it should be.
"Fuel Cutoff Mode occurs at high engine RPM or high vehicle speed to protect internal engine components from damage."

Now, I suspect fuel cutoff mode utilizes the engine shutoff solenoid which begs to ask. Once disabled, is the PCM's "Fuel Cutoff Mode" also disabled? In other words, does the PCM loose its ability to kill the engine should it detect a potentially catastrophic threat?

Then theres the never mentioned "Time Out Mode" thats often misdiagnosed as a faulty PMD and/or defective IP. Time Out Mode occurs when the PCM senses any significant threat or a potentially catastrophic event.
 

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So if this was disabled and for example you threw 25 lbs of boost at it would it no longer defuel ? ( not that I would actually put anywhere near that much boost at my truck just a example )


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Fuel is delivered under one of several conditions called "modes." All modes are controlled by the PCM."
A couple lesser known "modes" of the PCM include "Starting Mode" and an even lesser known "Fuel Cutoff Mode" that are only briefly mentioned in the manual elsewhere and not in the Control Module System section as it should be.
"Fuel Cutoff Mode occurs at high engine RPM or high vehicle speed to protect internal engine components from damage."

Now, I suspect fuel cutoff mode utilizes the engine shutoff solenoid which begs to ask. Once disabled, is the PCM's "Fuel Cutoff Mode" also disabled? In other words, does the PCM loose its ability to kill the engine should it detect a potentially catastrophic threat?

I find it hard to believe that "Fuel cutoff Mode" is written anywhere in the PCM to protect itself from high RPM damage when it is not even written in the PCM to shut off engine when oil pressure is gone (even though the PCM sees that too).

I'm pretty sure the FSS is a leftover from the DB pumps which actually needed an FSS and is a redundant shut off feature.

Do you remember what it turned out to be? guessing low voltage at plunger showing something else 10volts?

OP, my problem was a bad connection at the PS battery, FWIW.
 

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I find it hard to believe that "Fuel cutoff Mode" is written anywhere in the PCM to protect itself from high RPM damage when it is not even written in the PCM to shut off engine when oil pressure is gone (even though the PCM sees that too).

I'm pretty sure the FSS is a leftover from the DB pumps which actually needed an FSS and is a redundant shut off feature.
See attached..
 

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Touche :)

What does the next page say? (I really need a service manual)
see attached.. Yes, I only wished I would have purchased mine sooner.. Haynes and Chilton manuals are good for generalized crap, but often fail to get SPECIFIC nor OUTLINE many troubleshooting precedures.
 

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Agree or disagree, anyone?

Can anyone answer the question?


Could be the 'Engine Shutoff Solenoid's real function is misunderstood.

Engine Shutoff Solenoid
"Circuit Description: When the ignition switch is in the "OFF" position, the Engine Shutoff Solenoid is in the "NO Fuel" position. By providing a ground path, the PCM energizes the engine shutoff solenoid which then allows fuel to pass into the injection pump."

Also found elsewhere in the GM service manual.
"When not activated by the PCM, the engine shutoff solenoid blocks fuel flow from entering the transfer pump inside the injection pump and stops engine operation."

Thats practically all thats mentioned about the Engine Shutoff Solenoid in the service manual... Much like the fuel solenoid, PMD, or OS, the engine shutoff solenoid wasn't included in the ON-VEHICLE SERVICE section that included virtually everything else.

Although designated as the "engine shutoff solenoid", it might best be described as the PCM's "Emergency Engine Shutoff Solenoid."
Try to think of it more as the PCM's primary panic button instead of just an redundant 'ON-OFF" switch...
The other "fuel solenoid" is activated by the Pump Mounted Driver that is controlled by the PCM.
When the ignition is switch'd "OFF", the PMD cant communicate with the PCM thus "engine shuts off" as others have confirmed by removing the Engine Shutoff Solenoid's plunger yet engine shuts off under NORMAL operating conditions.....

I stress NORMAL operating conditions because the PCM has a several other operating modes besides the more common "Normal" (open) and "Diagnostic" modes.
"Fuel is delivered under one of several conditions called "modes." All modes are controlled by the PCM."
A couple lesser known "modes" of the PCM include "Starting Mode" and an even lesser known "Fuel Cutoff Mode" that are only briefly mentioned in the manual elsewhere and not in the Control Module System section as it should be.
"Fuel Cutoff Mode occurs at high engine RPM or high vehicle speed to protect internal engine components from damage."

Now, I suspect fuel cutoff mode utilizes the engine shutoff solenoid which begs to ask. Once disabled, is the PCM's "Fuel Cutoff Mode" also disabled? In other words, does the PCM loose its ability to kill the engine should it detect a potentially catastrophic threat?

Then theres the never mentioned "Time Out Mode" thats often misdiagnosed as a faulty PMD and/or defective IP. Time Out Mode occurs when the PCM senses any significant threat or a potentially catastrophic event.
 

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I can think of a few people on this site that may be able to answer that question, not me.

It's going to take a tuner, or at the very least, someone who has been inside a PCM/ECM and knows what they are looking at.
 

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I don't know "the answer" either. But theoretically, it would seem to me if the FSOS has a function other than the redundancy of being down stream of the PMD/FSOL electrical shut off it would be to prevent fuel being siphoned out of the IP housing and FFM via the return line after engine shut down. That might cause extended cranking times for the next cold start. But I also haven't heard anyone report that problem after removing a FSOS plunger... unless they just haven't noticed it. ~FH
 

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I can say that since I fixed my battery connection that my truck starts like an old Cummins, half a rotation. I have not had a plunger in my FSS for quite some time (close to a year, maybe?)

I won't get a chance to do a real cold start till February or so though :)
 
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