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Suddenly no throttle

WarWagon

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65 - APP 3 circuit range fault
This is a code pointing to the APP I warned you about. I don't recall 100% if it's this specific code, but, we can verify it quick enough.
Engine off key on:
1) Clear the codes.
2) See if the code is "cleared".
3) Slowly floor the throttle and let it back up several times.
4) Check for the APP code again.

You can watch the voltages change, esp the % throttle commanded, as you move the throttle - should be smooth and linear without jumping to 5V or 0V at any point. ECM's also lie and report table data when a fault happens as automotive electrical is "noisy" and vibrates. So you may not see the fault until it is present for like 30 seconds. This keeps warranty claims down for intermittent connections that mostly "just work".

For fun, best I recall, to set the ghost code turn the key off and pump the throttle and have it anywhere but idle for the next 30 seconds. Aka as long as you get numbers changing after key off in GMTD scan.

FWIW I chased this damn code as I had a kinking shut fuel hose that would vapor lock starve the IP for fuel and cause the engine to quit. I found the hose problem later. Swapping the ECM, and APP didn't cure the code and I inspected every inch of the APP wires to the ECM. Want to know where the other connector is like 1' away from the ECM? 🤪

After checking grounds and battery cables including a load test of each battery then verifying bubble free fuel coming out of the IP... I would try the spare PMD first. If you are dead set on an APP and ECM before doing an IP find a friend and borrow known good parts.

FWIW running out of fuel or air in fuel causes surging etc. It's the number one step in the GM manual : Verify no AIR in fuel.
 

dbrannon79

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I see your point @WarWagon especially when I see these numbers on the APP with a drastic change in the RPM and the pedal virtually in the same position! I took these photos with my phone while feathering the pedal. APP signals are almost identical.

1610515124245.png 1610515178576.png
 

dbrannon79

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Where did you get the PMD extension cable? It occurred to me some have had trouble with poor quality cables.
it was a purchase from Amazon. made in china. this may also be a culprit and didn't think about that. wires are thinner than whats in the OE harness. I may look into using the connectors and create a homemade cable using heavier wires just to rule out this as a possibility before throwing too much more money at diagnosis. afterwards purchase a better cable.
 

JMJNet

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I think Leroy probably still sells cable for PMD extension.
He made his own cable and have been doing it ever since he is a vendor for 6.5L.

If the PMD is still inside the hood, relocate it outside the hood.
Most put it in the bumper or in front of the radiator behind the grill.
That location have the best steady ambient temperature better than anywhere inside the hood since the temp usually fluctuates.
 

WarWagon

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On a heatsink plug the PMD into the factory harness without any extension.
 

dbrannon79

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On a heatsink plug the PMD into the factory harness without any extension.
I would try that but I can't get the plug out far enough to reach. it was a chore to get the extension connected without pulling the intake!

on a side note I went on a drive out of town today I'm guessing about 50 mile trip and all went well. altough just by listening to the motor during the trip going uphill on different occasions I noticed what sounded like the IP ( i thought was normal clatter) quiet down and then later on the diesel clatter would come back to what I am used to hearing. There were a couple of times where all I was hearing was my 4" exhaust as if I had a gasser under the hood and I wasn't pushing it very hard at all! that's making me think the IP is trying to tell me something. Of course it never smokes while driving, only on startups for brief seconds. I have tried to goose it before just to see what the truck would do and I barley get anything visible that I can see in my side mirror. Thats even carrying am 8' fiberglass camper shell with crap in the bed!
 

WarWagon

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Any new codes or returned codes today? You cleared the codes right?
 

dbrannon79

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something I forgot to mention that I just remembered. while I was out today I ended up in some heavy traffic, I realized that even though I can't seem to easily hold 1200 RPM while parked, it's relativly easy to keep the truck crawling in slow traffic with RPM's between 900 and 1200. I thought that was kinda odd that I can keep it steady at low RPM in drive but not while in park!
 

MikFish

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Similar situation, I replaced the throttle pedal sensor under the dashboard. Mine had just gone to idle speed with no acceleration. Could get it back if I shut completely off and re-started. Once I replaced it, no longer an issue.
 

dbrannon79

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Similar situation, I replaced the throttle pedal sensor under the dashboard. Mine had just gone to idle speed with no acceleration. Could get it back if I shut completely off and re-started. Once I replaced it, no longer an issue.
Thanks for the heads up. Ive got another APP on order. should arrive this afternoon. although the no throttle incident hasn't happened again I'm hoping that this will fix that and the thing where I can't hold the lower RPM steady in park. But I have a strange feeling in the back of my mind that the IP is warning me that it's time. she's got 275K miles now, I'm sure the IP was replaced at some point before I bought the truck but I figure I might as well start gathering parts and making plans to do the job soon. I figure if I'm going there I might as well look at a timing chain, water pump, and a set of marine injectors. I found out I can get a reman IP at my local Advance auto for around $700, not sure if that's best or just finding one in a junk yard and having it rebuilt.
 

MikFish

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I just upgraded my water pump and fan this past summer as well as relocated my PMD module to the inside of the bumper. I got all the parts through Leroy diesel, and have not been disappointed. My truck is now running about 20 degrees cooler.
 

dbrannon79

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I just found a post on another forum talking about the myth in marine injectors, so I suppose stock injectors it is.. my local Advance lists a couple of options available. BWD brand in reman and new, and Carquest reman and new. are there any drawbacks to which brand or the difference between reman and a new injector? I figure the reman ones have been tested before being sent out for sale. the BWD brand come with a 3 year warranty. I've also seen AC Delco and Bosh listed on Amazon for a decent price too.
 

WarWagon

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X2 on good injectors. The Commie China nozzles used in cheap rebuilds last 30K before they start sticking. Otherwise they are good for 100K miles. What CHEAP choice do you think your local parts store carries? Check the carnage thread for the melted and locked up piston a worn out injector gave to me.
 

dbrannon79

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X2 on good injectors. The Commie China nozzles used in cheap rebuilds last 30K before they start sticking. Otherwise they are good for 100K miles. What CHEAP choice do you think your local parts store carries? Check the carnage thread for the melted and locked up piston a worn out injector gave to me.
yipes! they do show new Bosh and new AC Delco but they don't list them under application. I have to greb the GM part numbers to find them. which is a better one between Bosh and AC Delco? I looked on Leroy Diesel and Quadstar and both sites show Bosh. I've seen issues with the Bosh glow plugs breaking the ends off. are their injectors better?
 
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