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If it’s a ‘94 (or any OBD1), codes can be cleared by holding both the brake and gas pedals to the floor, then turning the ignition key to the run/on position and waiting for 10-15 seconds. Then key off, release pedals, key back to on to recheck codes. You should get the 12-12-12 result if all cleared.

Oem FSO solenoids were on eBay for $50 recently.

If you’re willing to spend that $50 on the troubleshooting process, and given your results so far, I would strongly recommend installing a gutted FSO to cross that off your list as a potential root cause. You’ll then definitely get a constant DTC13, but you could then confidently proceed to look elsewhere for the source of the no-fuel issue.

If a gutted solenoid allows the truck to run, you can install your new solenoid and keep the gutted unit as an invaluable troubleshooting tool.

Despite the apparent design redundancy of this solenoid, there’s been some interesting past discussion here that suggests that the FSO can be commanded to close by the ECM in certain dire circumstances in order to protect the engine. No definitive proof to offer, but that certainly makes good sense.

The truck will run all day with a constant DTC13 (ask me how I know!), so that error code is NOT the source of your problem. To be clear, the ECM is not defueling the IP due to seeing the DTC13 present.

Also, the quality of products from the wiring harness supplier for 94 (and 95, iirc) is known to be problematic. If push comes to shove, high quality replacement harnesses are available through members/vendors on this site. Not cheap but reasonable, and that sure ended my occasional “dying in the intersection due to no-fuel until I wiggled the harness just right” problem. And this after EXTENSIVE probing with a meter to try to find the intermittent short/open that was causing the issue. (I also tried a new ECM to no avail. But another very useful spare to have for troubleshooting purposes.) Truck has actually been rock solid dependable for 20k since the engine harness replacement. Nice to be able to spend time on upgrades rather than constantly troubleshooting.
 

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All of these started because of using starting fluid and run out of fuel.

Did you check if the fuel is there?
You said, you replaced the OPS or not?
OPS controls the LP when engine is running on a 94 and it has caused a lot of issue in 93-95 model year.
I would replace with ACDelco OPS ONLY.

Yes, OPS can show oil pressure but the part that control the LP can still be bad.

Are you sure the IP in there is good?
The PMD is good?
 
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Discussion Starter #63
If it’s a ‘94 (or any OBD1) ... <snip>
Thanks RedShift, very useful. I should add that on this truck an exhaust gasket failed and was blowing very hot exhaust up behind the engine for a bit, enough certainly to smoke some insulation here and there. It was some time ago, but maybe that has something to do with it now.
 

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Discussion Starter #64
All of these started because of using starting fluid and run out of fuel. Could be... but why?

Did you check if the fuel is there? Yes
You said, you replaced the OPS or not? Did not
OPS controls the LP when engine is running on a 94 and it has caused a lot of issue in 93-95 model year.
I would replace with ACDelco OPS ONLY.

Yes, OPS can show oil pressure but the part that control the LP can still be bad.

Are you sure the IP in there is good? No, but I have no reason to believe at this point that it's not.
The PMD is good? Appears to be.
Are you saying the OPS controls the LP or the IP? I am sure the LP is good because I get ample pressurized fuel coming out of the return line at the IP, T valve, and fuel filter bleeder valve when it's running. I can also hear it, since it runs for a second or two when done cranking while the oil pressure signal is still over the threshold.

What is definitively THE problem is that the PCM is only sending 3-4 fuel pulses to the PMD-->IP, and then shutting it down. The question is why is it doing that? A quick look at the PCM source code would probably answer that... sigh. Has anyone ever seen that published anywhere?

Tangentially, shouldn't the OPS also throw codes if it's working not right? I can see that the PCM could be using the OPS for some sort of feedback, but it's supposed to be the case that if you simply disconnect the OPS, things should run in a limp mode. When I do disconnect it, I get no fuel pulses, but I read somewhere I might have to crank for 10-15 sec for them to start if it's in "no OCS" limp mode (I'd be there's a software timeout).
 

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OPS controls the LP (Lift Pump, it is an "L" - ELL not "I) when engine is running.
There is no fuel going during cranking in a 94, unless, it is mod with an additional relay.
So, if OPS is bad (the one that controls the Lift Pump), the LP will not start running as soon as the engine catch.
That is why we put 12V direct into the Lift Pump with an "L" not "I" when testing the Lift Pump with an "L" not "I".
Then we bleed the air and start cranking.
Everything have to happen at the same time, now you have fuel to the Injection Pump with an "I" not "L".
Then the Injection Pump electricity needs to be there.

Did you ever replace the Glow Plugs?
They may already burnt due to the starting fluid.
 

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OPS completes the circuit to the LP only. The ECM bypasses the OPS to run the pump during cranking to start, then the OPS takes over providing current to the LP when the key is released to the run position. This allows a low oil pressure condition to cut power to the LP in the event of an accident or oil supply failure, potentially saving the engine and/or minimizing the chance of fire.

As previously noted, if you have fuel flowing well at the filter drain t-valve during cranking, your LP is working. If the engine were firing during cranking but dying as soon as you release the key to the run position, that would point to a possible OPS failure. Since you’re getting fuel to the IP during cranking, but no fire, it seems unlikely that the OPS has anything to do with this. If ever in doubt, you could simply jumper it’s contactor terminals to confirm.

Afaik, the source code has not been published. But I believe there has been some work on that front by members here. Ask Buddy or Quadstar.
 

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The OP has a 1994 with OBD1.
LP runs WHILE CRANKING via the CRANK FUSE and then when oil pressure has built up.
The PCM has no control or input from the LP.
96 and up OBD2 went to PCM control and there is a code for low voltage @ the LP.
That code still has no effect on the engine running.
The OPS on an OBD2 is a backup/redundant part and is really not needed.
In fact the 6.5 diesel Vans after 1999 don't even have one.
 
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Discussion Starter #68
Update:

The both-pedals-down-clear-PCM-OBD1-codes procedure didn't work unfortunately. Tried it a few times and with some minor variations. Perhaps this was something they added in a later software update?

To attempt to clear PMC codes, I disconnected the battery for a while, swore at it for a bit while I had to put the GM cr-p side post stripped battery bolts back in, and indeed, got 12's.

Cranked it a few times with some of the glow plugs still not in (thanks, Rock, still waiting), and still got 12's.

Not sure why the code 13 wouldn't clear on its own, as indicated it would in the GM service bulletin. Perhaps a software update?

I'm not sure what all that means yet, but the next step is to throw the scope back on it.

I'm going to speculate that DieselPro's diagnosis some time back of a broken armature on the fuel metering solenoid is looking like where this is going, but the 3-4 fuel pulses and out PCM response is one I don't want to be defeated by.

I haven't read up on PCM software updates, but it this something I don't want to touch? I'm sure I can do it, but I don't want to create a bunch of needless unrelated headaches.
 

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Update:

The both-pedals-down-clear-PCM-OBD1-codes procedure didn't work unfortunately. Tried it a few times and with some minor variations. Perhaps this was something they added in a later software update?

To attempt to clear PMC codes, I disconnected the battery for a while, swore at it for a bit while I had to put the GM cr-p side post stripped battery bolts back in, and indeed, got 12's.

Cranked it a few times with some of the glow plugs still not in (thanks, Rock, still waiting), and still got 12's.

Not sure why the code 13 wouldn't clear on its own, as indicated it would in the GM service bulletin. Perhaps a software update?

I'm not sure what all that means yet, but the next step is to throw the scope back on it.

I'm going to speculate that DieselPro's diagnosis some time back of a broken armature on the fuel metering solenoid is looking like where this is going, but the 3-4 fuel pulses and out PCM response is one I don't want to be defeated by.

I haven't read up on PCM software updates, but it this something I don't want to touch? I'm sure I can do it, but I don't want to create a bunch of needless unrelated headaches.
With the scope attached, I would try different "known working" PMD's w/resistor installed, and see if you get any different readings on the pulses.
Also, verify that the ground wire for the OEM PMD harness is attached to the top of the IP and is tight
 

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Might as well clean and check the ECM grounds atop the #8 cylinder stud while you’re at it. (If you havent already.).

Very strange that the DTC reset procedure didn’t work. Here is where I should probably mention that when I bought my ‘94 it was not running due to a no fuel condition. After troubleshooting for a month worth of evenings I gambled on trying a non-returnable replacement ECM. Fired right up afterwards. If you can find a known good spare to swap in as a test, I’d sure give this a shot. Wrecking yard, possibly?

AFAIK, there have never been any updates for the ECM/PCM firmware offered by GM. As mentioned earlier, Buddy and Quadstar have done some heavy lifting in this arena, and are able to provide retuned versions of the firmware on the OBD1 chip.
 

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Discussion Starter #71
With the scope attached, I would try different "known working" PMD's w/resistor installed, and see if you get any different readings on the pulses.
Also, verify that the ground wire for the OEM PMD harness is attached to the top of the IP and is tight
Thanks, Ok'.

I am an electrical engineer and have designed and built hardware and software for many an embedded systems (aka "smart toaster" or "robot"), which is exactly what this is. So it irks me to no end that I have to reverse engineer what the PCM is trying to do through experimentation. Oh, for the want of some source code! Problem would be discovered in 5-10 minutes.

Incidentally, I hear you on the grounds, but I am pretty sure they are good based on what I have seen on the scope and tested. Also, the fuel metering solenoid is driven on both ends by the PMD (i.e one circuit pulls it up, another connects it to the ground PMD's ground, so there's a voltage across it). So as long as the PMD ground and the PCM ground are pretty solidly grounded to each other, neither should be affected by other grounds or loose ones with regard to fuel metering. Anyway, I'll go through all that again, especially now that the code 13 is gone.

Lastly, in reading around, it appears that more extensive diagnostic info can be gleaned with the right GM scanner on this thing. I happen to have a SnapOn MT2500 "super deluxe scanner" (super deluxe is what I need...LOL!) and I just discovered it has an OBD1 connector among many in the kit. Anyone used one of these? It has a phone book sized manual, but heck, I'll take it home tonight for some fun reading no doubt.
 

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Thanks, Ok'.

I am an electrical engineer and have designed and built hardware and software for many an embedded systems (aka "smart toaster" or "robot"), which is exactly what this is. So it irks me to no end that I have to reverse engineer what the PCM is trying to do through experimentation. Oh, for the want of some source code! Problem would be discovered in 5-10 minutes.

Incidentally, I hear you on the grounds, but I am pretty sure they are good based on what I have seen on the scope and tested. Also, the fuel metering solenoid is driven on both ends by the PMD (i.e one circuit pulls it up, another connects it to the ground PMD's ground, so there's a voltage across it). So as long as the PMD ground and the PCM ground are pretty solidly grounded to each other, neither should be affected by other grounds or loose ones with regard to fuel metering. Anyway, I'll go through all that again, especially now that the code 13 is gone.

Lastly, in reading around, it appears that more extensive diagnostic info can be gleaned with the right GM scanner on this thing. I happen to have a SnapOn MT2500 "super deluxe scanner" (super deluxe is what I need...LOL!) and I just discovered it has an OBD1 connector among many in the kit. Anyone used one of these? It has a phone book sized manual, but heck, I'll take it home tonight for some fun reading no doubt.
There have been many reported threads about the Snap-on scanners not giving the correct timing values for the 6.5L
OBDI software recommended is the GMTDscan tech and cable to a laptop..
 

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Discussion Starter #73 (Edited)
AH!!! Thar's Yer PRAHBLAHM!!!

And the prize goes to.... DieselPro! Ding! Ding! Ding! Ding! Ding!

Well, let's not get carried away.

So I took off the lower manifold and disassembled the fuel metering solenoid end cap to examine the armature, as suggested by DieselPro and referencing this post by quantam mechanic:


Sure enough, after looking closely, there is a small hex cap screw that attaches the armature shaft to a steel plate. As the solenoid is energized, this plate I believe closes a magnetic circuit, and that is somehow sensed by the PMD and fed back to the PMC.

(Theorizing here on the functionality FWIW: In physics terms, magnetic fields like to travel through certain materials, like iron/steel, much better than say air or diesel fuel. They go around in a complete circle, through the easiest path, much like electricity. Magnetism and Electricity have a lot of influence on each other, without getting into the weeds. When there is an "air gap", which is the case when the solenoid is retracted, the field behaves differently and has less magnetic force than when there is no air gap. Thus, the way this thing seems to work, is it's electrically energized by the coil, causing the armature shaft to pull in and enable the pump cycle, while at the same time closing the air gap. That in turn affects the magnetic field and hence the current going through the coil, which is sensed by the PMD on the same wire that is driving the coil. Or something like that. Scope traces forthcoming for comparison.)

Anyway, This screw is BROKEN! So the plate isn't closing the magnetic circuit.

Pic's below:

635861


(Above) Sort of an exploded view of what you have to pull apart. The two pins on the left are the terminals that connect the wire harness to the solenoid itself. I sort of jacked up one of the insulators slightly trying to get them out.


635862


(Above) Hex cap screw in red is suppose to go through the hole in the metal place and screws into the end of the armature shaft. The screw is broken. It is lock-tite'd in there, so we'll see if we can get 'er out.

As the armature shaft goes in and out, the plate moves with it and opens and closes magnetic circuits that include the plate and whatever the coil is wound on (not shown).

I'll get it put back together and report back.

Hex cap screw: $0.10 at ACE (probably more like $0.02 normally)
New Injection Pump:$3500 quoted.

We'll see...

P.S. I just managed to get the broken screw out of the end of the shaft. It is LEFT HANDED. Yay.. dunno if ACE has left handed metric cap screws or whatever it is.... OD .108", 2.75mm. I heated it up with a torch to burn out the locktite. I might reheat and quench to re-establish the hardness before reassembling, but it's probably not necessary.
 

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I am quite sure it's not left handed. Just regular threads.. The shaft shows lots of wear so it might not work, at least polish it. The travel is only .005" so if it's not perfect it will throw a code.Just don't turn the solenoid in the head or that will be the end of it. (It's set on the bench with the head disassembled.) So folks this is what causes a runaway . > Broke or loose armature screw.
 

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Discussion Starter #75
I am quite sure it's not left handed. Just regular threads..

The shaft shows lots of wear so it might not work, at least polish it.

So folks this is what causes a runaway . > Broke or loose armature screw.
Oh, it's definitely left handed. It appears to be a 4-40 left, ~3/8" long. Can't find a 4-40 left anywhere though, 6-32 left, yes. I'm guessing it's left handed because the armature shaft wants to precess for some reason. It is also a metric 2.75xsomething...

Yes, polish.

Yes, broken or lose armature screw.

The point of most of this thread for me is (since we're not running yet...) to determine why it causes the problem (runaway or no start). It appears to be the case that the pump technically could operate, but somehow the feedback to the PMC is getting screwed up.

And yes, in a way, it's a big waste of time like you said, but I didn't want to start tearing things apart and also maybe it's now documented... :) Plus, I like the the challenge.

Anyway, as soon as I find the screw or another armature shaft (with a right handed thread), I'll put it back together and cross my fingers. Stay tuned.
 

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>> shaft wants to precess for some reason <<<< If you meant to say the plate is recessed the armature is not any good....We discarded shafts that had that much wear on the shaft and never tried to reuse one that the screw broke..... It just took way to much time to redo the whole pump, when it could have easily been replaced the first go around. They are quite precision and would not pass calibration specs once ran. I am curious to as why they runaway and just don't die when broke. Typically the truck will sit there idling perfectly and you just barely touch the throttle and then away it goes wide open. Your best bet now is find a good used one from one of the members here... A new one is a little expensive and the money would be better spent on a new pump.
 

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Discussion Starter #77
Some additional updates from my research:

Apparently Stanadyne had over time discovered issues with the fuel solenoid armature design, though screw failure doesn't seem to be one of them. They came out with a new design in early 2000's is seems, and that one was designed to have less friction.

From http://www.stanadyne.com/dealerportal/ssi/english/Service Bulletin/550.pdf

635897

And from http://www.stanadyne.com/dealerportal/ssi/english/Service Bulletin/561.pdf

635898


My pump has the armature assembly on the left above. The one on the right seems to be available for purchase through some dealers for about $80, but I'm not sure if it will replace the old one. Anyone know?

Interestingly, there is this "anti-rotation pin", which I think speaks to the left handed thread on the armature assembly.

I just called the regional diesel service shop I use and they said they can probably get most any part from Stanadyne. Stay tuned.

Also, I haven't found any DS4 parts diagrams or lists with part numbers. Anyone know if they are to be found publicly? (I hate it when they do it dealer only... I'm a DIY guy)
 

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Discussion Starter #78
Ah ha, someone else out there has discovered how it works too:

"The PCM sends a digital Fuel Inject control pulse to the FSD, which is (a) a power driver that applies battery current to the FS solenoid coil via the collectors of the paralleled PNP driver transistors, and (b) a comparator circuit that monitors that current for the changes that result when the flux density changes as armature\plunger begins moving, continues forward motion, and stops as the valve seats - the resultant digital Closure-Time pulse is sent to PCM which starts counting clock ticks for injection pulse width timing - PCM has been counting ticks since sending the injection pulse to the FSD, so CT is included in Injection Pulse Width timing - FS is merely a coil, responding to applied power - power on is a 1, coil energized, power off is a 0, coil de-energized "

In short, when the armature screw breaks or for whatever reason the air gap doesn't close by the movement of the armature, it screws up the closure time pulse, and thus the fuel mapping, which likely explains why the pulse width kept diminishing in the 3-4 pulses I was seeing from the PMC before it stopped putting them out entirely.

Still trying to figure out what armature I can find, or the 4-40 left handed cap screw. I found some stainless ones, but they are only 70,000PSI, vs 140,000PSI for a standard (grade 8) socket head. Given that the old screw broke, I'm not so sure one rated for half the strain will do it...

Also, the armature is rather scored at two places along the axis, in a rotational manner. I can polish it if I can find a replacement screw, but I think I'd rather just replace the whole armature assembly.

Does anyone know if the newer armature design is compatible?
 

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Best bet is to replace IP and call it a day.....Odds are the new armature will not work... The poppet lift is critical and it's not likely a replacement will still be in spec. They have to be set on specialized equipment. One other thing is the wear inside the IP where the armature scores the inside metal.
Spec is five thousandths.. Lift. Hard to set on the work bench with the proper equipment. Impossible to set on vehicle.
 
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