Engine Power Loss in Turbo Diesels
November 22, 2010
by Jim Bennett
I had a problem that may be common with other owners of GM 6.5 turbo diesels with electronic injection pumps. These trucks use what's called "fly by wire" accelerators. There is no direct link from the gas pedal to the engine. It's all done electronically.
I was experiencing loss of power when accelerating. It was more of a nuisance than anything else. You could just feel the slight loss of power like the engine wasn't getting a solid stream of fuel. It never stalled and could be corrected by just changing the accelerator pedal position. I thought it was bad fuel at first. So, first I replaced the fuel filter. That didn't fix it. After that, I tried changing the Lift Pump. That didn't do it either. I carry a spare PMD, so I changed that too. Still, it continued. I noted only twice that I had a CHECK THROTTLE LIGHT but didn't pay much attention to it thinking it was a fluke.
After putting up with this for a couple weeks I finally decided to remove the accelerator pedal, removed the pedal position sensor, and checked all three resistive potentiometers on the bench with an analog type ohmmeter. One of the three pots had a dead spot where there was no resistance change at some pedal positions. So, I decided to change it.
The problem I discovered was that the AM General replacement is not cheap. I was quoted about $730 for a new one from AM General but you can find the GM equivalent (15751307) or an AC Delco equivalent (213-2820) for anywhere from $285 to $500. The sensor is made by CTS Automotive Products (Series 503, P/N 2710) and probably isn't worth over $50 but they don't have any inventory and are almost impossible to find anywhere. I ended up with an accelerator pedal from a 98 Chevy C2500 pickup which has the same sensor. I removed the sensors from that unit and installed it today and it fixed the problem.
There seems to be a lot of similar reports for surging and most owners seem to be concentrating on getting their PCM reflashed by a dealer in response to an AM General Tech Bulletin. Frankly, I don't think a PCM could all of a sudden lose its memory and would need to be reflashed. So if that problem existed, it would be something that was always there and wouldn't all of a sudden just happen out of the blue.
The sensor is simple to remove but will require a TORX CR-VT 20 security screw bit to remove the two screws holding it. As far as cleaning the sensor; I didn't open the sensor, I figured I would probably destroy it in the process. It’s a sealed unit and would need some special technique (maybe an EXACTO knife or something like that) to try to get the cover off the housing).
Electronic Accelerator Pedal
The PDF is what I pulled out of the 2001 Maintenance Manual in might be helpful to others with similar engine performance surging or engine stumbling.