Hi,
I have posted a few times before and now I have another interesting problem
I have a 1996 chevey 3500 with a 6.5 turbo diesel. I had gone through the pmd and injecter cinerio a while back which wound up being a ground issue. MY Problem now is the
throttle ckt on the truck. It started out when I was sitting at a light idling,the truck for no reason throttled up as if someone stomped on the peddle!!! Luckely I had stepped on the brake peddle before I wound up in the back seat of the driver in front of me.
It throttled back down and I was able to drive it a few miles, but then it would start surging then slow down,surge and throttle down.
I shut down the truck and tried it later on again it then surged on me (accelerated)when I had a steady peddlle at 40 mph.It seems to happen when the truck warms up and it doesnt matter if the truck is in gear or park.It happens weather it is idling or throttled.
I have already replaced the accelerator position module on the peddle and swapped out the powertrain control module to only get the same results.I need to know what controls the throttle and or what else can cause this??
If anyone has overcome a similar problem, I would realy like to hear from you!! and when the problem is solved, I promise a return post as allways! SO PUT ON YOUR THINKING CAPS
AND HELP ME BEAT THIS PROBLEMANY INFORMATION IS WELCOMED.
Thanks guy's
Big Joe

 

PPS(pedal position sensor) controls the throttle on these trucks as there is no cable on these trucks sounds like you are having issues with yours???have you read the codes yet?

 

I had kind of the same problem,,,with no codes sent I ended up Replaceing the IP it was not my first choice... but it was an internal problem with my pump.... after all said and done, new pump and the trouble seems to be gone......Iam learning all kinds of things about these engines mine is a 98 6.5.....the old pump had 100,000 miles on it.

 

Ay Mahem and Dorian

The problem is the PMD. I had put a new injection pump in the truck last year after having stalling issues (wound up being inproper grounding) but it afforded me the opertunity to relocate the PMD that came with it, to a spot away from the engine on a heatsink.
I did change out the pedal position sensor(First thing and easiest to do) But problem still existed.I then ruled out the PCM board by putting in a loaner from my brotherinlaws truck,but I had the same problemas soon as the truck warmed up. I then did some research on these older PMDs and found out that they are rated at 185deg.and the new aftermarket ones are rated at 260deg(my engine here in florida runs at 198deg.) I took the older unit off the heatsink and just hung it in the open air. The weather had turned cool and overcast and I Ran it a week without a problem. I then experimented by putting in a PMD that was known to have problems and started the truck and imediately it started surging and acting up. I put the working one back in and it ran fine without problem until today.It surged twice for a short period when i was at a light, but as soon as I got going (producing alot of airflow to cool it down)It worked fine. Today was a very hot day and thats why it started to act up.
So through my lessons learned with my trucks fuel delivery system and the injection pump circuit, I found out that the PMD not only can shut down the injection pump, but can also in this case,send faulty signals to the injection pump controlling its timing and fuel rate. Besides a wiring condition, In my research and looking at the electrical diagram,there was only 3 things that controlled the throttle,(1) Pedal position sensor,(2)Pmd,or(3) the PCM. And to make matters worse, " IT THREW NO CODES!!!!!! So I figure the PCM processed the signall coming from the pedal position sensor and sent the correct output signal to the Pmd but the PMD did not output the correct throttle signal response to the injection pump because of an electronic component heating up within the PMD (such as resister,transister ex)the output value(I think) was effected because of the heat! for example; when a resister heats up(depending on its wattage rating) its resistance will change which changes the voltage value. If the injection pump depends on a resistive or voltage or current to increase or decrease how much fuel and the rate at which it injects it, it is using these values for fuel adjustment, then the Fuel pump will respond accordingly.
I can't say for sure how the PMD is desighned to work(I havn't seen a schematic of one)But I am almost sure this is whats happening.The resister or transister is not faulting or opening (if so the PCM would see this within the circuit thus indicating that a device is not outputing and the copponent is faulting and not functioning and throw a code)
This might sound like mumbo jumbo, but for some who have knowledge in electronics would easely understand what I am saying. I am relaying what I THINK IS HAPPENING internal to the PMD.If my assumption is wrong and and my problem is somthing else,I will not leave anyone with bad information! I will post again and make the correction.
I am waiting for the the upgraded PMD and will run it on a heatsink,and in a month or so, I will let everyone know how I made out.
Thanks you for responding Mayhem and Dorian!! I appreciate any input I CAN GET, sharing ideas have saved me alot of money and time and your responses are allways appreciated on my posts. Sharing information and solving problems is what this sight is all about RIGHT??? Thanks again, big joe