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.

 

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

 

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, 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?

 

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.

 

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.

 

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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Subscribed.

 

Touche

What does the next page say? (I really need a service manual)

 

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.

 

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.

 

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

 

Unless Im mistaken, theres a one way check valve built into the fuel inlet nipple of the IP to prevent that..

 

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

 

Someone needs to simulate a run away engine and report back,

 

Toyota owners need not apply. Check your floor mat. : ~FH

 

pulled c clip off fuel shutoff solenoid

after removing plunger which looks like small CO2 cartridge.....left air pocket and truck ran lousy. So my bypass so far a blunder. Put back together and found truck ran good again with 3/4 installed on threads. Was told by reliable diesel supplier that the fuel solenoids rarely fail......and they are a back up protection for runaway diesel.....keeps rpm under like 4300 rpm...my issue still on the supply side and trying to work it out...tested solenoid out of truck with 12v and can see move .......tried separate 12v should be working but something screwy...all the way threaded in .....no start......3/4 threaded in starts..weird science.

 

Sorry but I'm calling this BS

after removing plunger which looks like small CO2 cartridge.....left air pocket and truck ran lousy. So my bypass so far a blunder. Put back together and found truck ran good again with 3/4 installed on threads. Was told by reliable diesel supplier that the fuel solenoids rarely fail......and they are a back up protection for runaway diesel.....keeps rpm under like 4300 rpm...my issue still on the supply side and trying to work it out...tested solenoid out of truck with 12v and can see move .......tried separate 12v should be working but something screwy...all the way threaded in .....no start......3/4 threaded in starts..weird science.

 

These things are getting old, and remember they are electrical components. Having it tightened down may be torqueing something inside and causing a malfunction or misalignment. Why they are there in the first place is probably because, as mentioned earlier, Stanadyne at that time has built pumps for many years and they all needed a mechanical or electrical shut off mechanism. The electronics on this pump were revolutionary and having a shut off was something that was always done. Plus some government agency probably required it because of the same reason and liability reasons.

 

Plus some government agency probably required it because of the same reason and liability reasons.

This, they need to make sure it won't run away.

 

bump. Can any resident experts answer my FSOS question?

Also, can anyone confirm or deny the "Time Out Mode"?



Thanks

 

I've had two trucks in the shop that exhibited the Fuel Shutoff Solenoid Fault code.

The fix was simple once everything was tested out as working.

By tested out I mean positive voltage on one terminal on engine harness (enough to turn on a 12v test light) and a good ground on the other terminal (enough to ground and light a 12 test light). Then testing the solenoid with some jumper wire into it's terminal from a battery and listen for the click. Other methods of testing this work as well, this is the simplest in my opinion.

The two-pin connector that the solenoid connects to can be at fault. As the connectors wear (namely the one on the engine harness) the contacts in the female socket end of the solenoid (connector on the solenoid) don't make a good connection.

Just slightly bend the two contacts on the solenoid connector (female socket) to where they'll have some tension against the contacts of the connector of the engine harness.

Problem solved!

Hope this helps.

 

Has anyone noticed the tach not moving when cranking? I've checked the FSOS on the IP, and it does click, but perhaps doesn't function - don't know if the two are related....

 

This may sound the like most absurd question but to remove the solenoid is it the hex head on top that you turn or the whole body? Working in poor light I rounded that hex head and can't get a grip on it...it was/is incredibly tight.

 

that hex head is part of the whole body. If it is rounded just put some vice grips on it to unscrew it. You can do this on the hex or the body. It unscrews from the base.

 

I can say that the PCM cuts fueling by way of signals through the PMD at whatever RPM is programmed, which is about 3700rpm on stock tunes, and the max allowed by the PCM otherwise is around 4300rpm, which may be when it would kill it with the FSOS. So the FSOS is only needed for the freak situation that somehow the PMD is just outputting signals for more fuel and the PCM cannot control it. So fracked up PMD is the only problem where I see the FSOS possibly being of use. This was unheard of before Flight Systems started making them.

 

Same here, I can see in the prom where the tunes cut fuel based on RPM but the base ECU logic is something we will probably never see :thumbsdow

 

IDK... All the information and techno babble BS I read keeps pointing to the PCM as being in CONTROL of the "Fuel Cutoff Mode," not the PMD..

PMD, in a nutshell, is little more than a POWER AMPLIFIER. It simply cranks up the PCM input signal(s) required to RAPIDLY activate the Fuel Solenoid, not to be confused with the ESO...

To fully exlain requires alot more than can be summed up in a few short paragraphs..

The condensed short version is the PCM PROCESSOR(s) cant safely provide the POWERFUL impulse(s) needed to repeatedly trigger the Fuel Solenoid without damaging the processor so it employs an army of quad drivers to operate and/or monitor the many individual components making up all the necessary (and/or EPA mandated) operating systems.. Still unable to safely provide an amplified signal to the Fuel Solenoid, enter PMD..

IMO, its this interface and interaction (thus reaction) thats greatly MISUNDERSTOOD and instrumental in the creation and perpetuation of the mythical PMD Goblin...

Its a deep DEEP subject, not sure I want to lead off the paranormal bucket brigade.
Everytime I try, I get ASE Certified WAZOO's talking 'bout how they dont know jack...




To sum it up in a sentence. PCM Ghost are frequently being MISIDENTIFIED as just another passing PMD Goblin.

 

‘Upset’ G.M. Engineer Spoke in House Inquiry


G.M. ‘Bullied’ Manufacturer Over Poorly Designed Part, Email Says

DETROIT — General Motors pressured a supplier to continue producing a substandard ignition switch a decade ago and leaned on the company to improve it even though it could not be fixed, a newly disclosed email shows.

















No,,,, GM wouldnt create mythical creatures to avoid NTSB recall of 6.5's

 

Excuse me while I yawn. EVERY OEM has been caught doing bad things, biggest one to date and even bigger than GM is Toyota's tendency to run away when they switched to fly by wire engines. Sorry, but as long as the mighty dollar controls us, then this will never stop. You have 2 options, deal with it or buy and maintain older vehicles. I prefer the latter.

 

The PCM does control the fuel cutoff mode and the FSOS, but the PCM also controls the input to the PMD obviously, which is what controls the output to the IP's Fuel Solenoid. And because the PMD is basically just a power amplifier, the PCM can cut fueling by just stopping the signals to the PMD. This is obviously how the PCM meters fueling out of the IP, and its how it governs at the programmed RPM limit of about 3700rpm and speed limiter of 98mph.

The PMD can be corrupted into sending fueling signals to the IP, by way of EMI or whatever that might resemble a pulsed signal. It will probably interpret some low RF signal as an input and amplify it, driving to higher RPMs, and this is the one scenario the PCM would need to control the FSOS to cut the fueling off. Its not supposed to be susceptible to that, but things break down, and it wasn't an issue with the original PMD design. My guess is that EMI is what leads to most PMD related faults, and heat could be a factor in instigating those issues. Actually grounding the base of the PMD would help eliminate EMI within itself. The only issue is if the transistors were to lose their isolation from the PMD case, because the body of the transistors carry power. Thats why the PMD design uses so many insulating methods to avoid grounding it to the engine, and probably its worst problem. I personally make sure that its grounded, scratch/sand off some anodized coating and ground it, put a 1-amp fuse in line to ground if your'e worried about the transistors shorting out to the case.

I have observed the PCM to PMD and PMD to IP signals on an O-scope, and when the PCM is in one of its no-start modes, those signals are absent, and even without the FSOS, it won't start.

 

Grounding PMD Case

Hey there 94C1500,

Great explanation! Spot on. EMI is the bane of all data systems, and since our IP's operate using data streams, it's a good probability that EMI is the cause of many of our PMD/PCM failures (especially intermittents!).

I've been chasing a no start issue, and just finished verifying all of the grounds. I found the PMD case itself was not grounded for better EMI shielding.

When I sanded off the anodized coating on my PMD, I found that the metal base was warped, by as much as .020 inch. This may not sound like much, but it's enough to warp the PCB inside the PMD. This reminded me of what Mark (H Diesel) stated earlier, about the possibility of age, and unequal "physical" stress on electronic/electromechanical components causing failures.

Unfortunately, this did not cure my No Start issue

Jack

 

Hey there 94C1500,

Great explanation! Spot on. EMI is the bane of all data systems, and since our IP's operate using data streams, it's a good probability that EMI is the cause of many of our PMD/PCM failures (especially intermittents!).

I've been chasing a no start issue, and just finished verifying all of the grounds. I found the PMD case itself was not grounded for better EMI shielding.

When I sanded off the anodized coating on my PMD, I found that the metal base was warped, by as much as .020 inch. This may not sound like much, but it's enough to warp the PCB inside the PMD. This reminded me of what Mark (H Diesel) stated earlier, about the possibility of age, and unequal "physical" stress on electronic/electromechanical components causing failures.

Unfortunately, this did not cure my No Start issue

Jack

I had a similar problem and I hear 94 wiring was not great. This was my no start issue.
http://www.dieselplace.com/forum/63.../forum/63-gm-diesel-engines/21-6-5l-diesel-engine/788826-94-stall-no-start.html

 

jakl did you ever solve your no start issue?