Very strange PCM/ECM issue

600 Megawatts

600 Megawatts

Many Irons in the Fire
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May 6, 2008
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Ok, this is a different one fo sure.... I have an 2001.5 HO, BUT its a P pumped conversion ... Zero issues for 4 years.. Now all of a sudden, I get a hot restart condition, where the gauges are all dead, (including tachometer) the wait to start light flashes, and the alternator wont charge, and no other truck electronic equipment will work as if the engine is running, for instance the seat heat, the A/C etc. When the engine is cold, zero issues. Now, I know that the PCM gets a tach input from the ECM, and wont fire the alternator field, nor allow A/C or seat heating until the engine is above 400 RPM (engine started). And when in the hot condition and the problem is present, I dont have any tach signal, so that makes sense. SO this seems to be an ECM issue, not a PCM issue. The PCM is just doing its job, it has no clue from the PCM that the engine is running. Mind you the ECM does very little at this point, as the VP 44 is long gone.. It only takes care of the gauges, the tach, and the intake heater etc... I have the lift pump and the P pump fuel shutdown solenoid wired through a separate relay to keyswtich on, so the engine will start and run just fine, regardless of the ECM condition, and if fact the ECM doesnt even need to be present for the engine to run now with the P pump. I have had a check engine light and tons of codes since day one of the P pump conversion of course, but thats because there is no throttle position sensor, nor any VP 44, so pulling codes is totally futile, there are dozens of them...


Now, seing that I have no problem when the engine is cold, only when the engine is hot, I tried hosing the ECM down with cold water. no change. I then tried hosing down the PCM with cold water... nothing... the issue persists until the engine itself has cooled... The other interesting thing is that when I do start it cold, the oil pressure gauge goes to around 80 PSI and does not move no matter what. I can stall the engine, leave the key on, and the oil pressure stays at around 80 psi. Mind you, I have an actual gauge installed on the oil pressure rail under the hood, and its showing the actual pressure, which of course varies from 25 Psi, to around 70 psi depending on RPM and temperature, so that is the real deal. The other thing I notice is that, even though its hot outside right now (90F), it seems to be cycling the intake air heaters for over 10 minutes after a 'cold' start... This does not compute... Perhaps something is wrong with the IAT, and it is both giving a false signal to the ECM, and perhaps dragging the sensor bus voltage down also messing with the oil pressure sensor, and when warm, ready for a re-start, the ECM is saying, whoa, things are way out of whack and hanging ??

Realize this is a long painful post, and a weird one, but maybe someone else has been here... I am not a fan of just changing parts, I like to troubleshoot, analyze and execute.


Let me know what yinz think.

Kp
 
Sounds like you have two problems, so you do have fuel pressure? If so what kind of fuel shut off do you use mechanical or electrical. You check and see if you have power to the fuel solenoid if you have one.
Could crack a couple lines see if you have fuel to the head.
For the gauge deal sounds like ECM shot but need to get it running first.
 
Sorry seen you had an electric solenoid could try tapping it when the problem exists. Your truck should run without the ECM. There should be a screw or some way to bypass the solenoid like the old cummins pacer pumps.
 
Have you put a scanner on it? DTC's?

Sounds like a cam sensor going bad to me.
 
i had a similar issue with my 98.5. try checking the two small ground cables off the passenger side battery. i had one wiggle lose inside the connecter and it was hit or miss when it would act up.
 
Well I look retarded thought it wasnt starting when hot. Sorry trying to help with a problem that doesn't exist.
 
Cam gear starting to walk its way off and cam sensor not picking up all the time? That shouldn't make the grid heaters cycle though.
 
2001ctd2500 said:
Cam gear starting to walk its way off and cam sensor not picking up all the time? That shouldn't make the grid heaters cycle though.
Click to expand...

It wouldnt even register cold though I would think. Im sticking with heat soak on the cam sensor.
 
Well I no I was totally off before but when my ECM failed it did some of the same things. Wait to start would flash and coolant gauge done stupid stuff. Luckily found an ECM off an 02 dully ho from junk yard and all is well for a year now.
Could find a friend maybe to lend one but it has to be an ho though I think.
Hope this helps this time.
 
Ok, thanks for the replies gents. Yes, I should have been more clear, the engine starts and runs fine, because its P Pumped, I am just losing all the other gauge functions, and the vehicle functions that require the engine to be confirmed to be running, like A/C, seat heat, and most importantly the altnernator field.

Im leaning towards a heat soak issue also, just not sure where. I thought it was most likely the ECM or PCM itself, but hosing that with cold water had no effect. I am somewhat doubtfull about the cam sensor though, because it will do it once you turn the key to ign on, and dont crank it yet... So if you are never trying to turn it, the cam sensor isnt pulsing anyway, so the ECM should not care... unless the cam sensor is failiing with heat soak in such a way that its dragging the sensor voltage down... I suppose I will try disconnecting it... Obviously I wouldnt have a tach then, but at least see if its changing anything else.. I am leaning towards the IAT sensor so far.. Because even when the engine is ambient temperature and I get everything to work, its cycling the grid heaters when they are clearly not needed.... Tomorrow I will start unplugging stuff.

THanks for the replies

Kevin
 
Unplugging the cam sensor will duplicate the issue you have, no tach, no charge, no A/C. These things will not work unless the ECM and PCM have engine speed which comes from the cam sensor on your engine.

I still didn't see if you've put a scanner on it when it is doing this. That would be the first thing I'd do. Tell us what DTC's are present. You should be able to monitor cam sensor signal. If you don't see it, I would say that's your problem. If you have access to another cam sensor I would try swapping it out and see what happens.
 
Scanner is totally futile. With a P pump conversion, the ECM is totally out of its mind and there are no less than a dozen codes, and half a dozen companion codes.. Remember, the VP44 isnt even there, the Accelerator Position sensor isnt there, when the engine is running, the ECM doesnt even know why its running, because of the above... etc etc etc. So tons and tons of codes.... I quit even looking at codes years ago after the conversion....

Didnt get to tinker with it today.. will try tomorrow.
 
It should not have a code for the cam sensor if it is working. Scan the truck and see.
 
Could you not clear the DTC's and see what comes back? I usually write down what codes are there, clear them, test drive, and then compare.
 
I obviously don't have a VP (or a MAP sensor for that matter) on my truck, either, and I only have these recurring codes:

P1693 – DTC detected in companion module
P0237 – MAP sensor voltage too low
P1689 – No communication between ECM and Injection pump module

I don't know what should show up without the APPS.
 
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