Newby to diesel bombers. I have 1997 GMC with 6.5 turbo. problem is, when leaving town my truck started bucking/ surging. rpms go up to 2000 then drops to practically nothing over and over as long as truck is running. There is no response from throttle just constantly revs up and down. changed fuel filter and bleed out air. still same issue continues. I replaced pmd with s&s diesel fsd w/ heat sink 6 years ago and relocated it to the top of air plenum as instructed. Also has K&N air filter. otherwise stock. Truck is over fueling extremely. Black soot fills neighborhood as soon as I start truck. I am currently chasing fuel system for air in system, in-between rain showers. only codes are for engine over speed and fuel solenoid slow response. Has history code for P0101 mass air flow sensor that was replaced 6 months ago, with check engine light going off after new MAF. Checking out lift pump and for air in system, was wondering if anyone else has had this problem. If no air found in system and lift pump ok, hate to start replacing PMD's or IP or Injectors blindly. Truck starts right up, (even at 30 below this past winter when block heater was plugged in) Has no stalling or dying issue. just runs away with it's self. I don't suspect any wiring issues currently due to no codes for any of the sensors. Any help would be appreciated.

 

You have a 6 year old PMD on top of the intake ? if so get a new PMD and locate to rear of the front bumper with a 6ft extension harness also do you have a peice of clear fuel rated hose to the injector pump so if you are sucking air you will see it. clean all grounds especialy the one on thhe rear passenger side cylinder head bad grounds are no good for a 6.5.

 

used clear hose yesterday on inlet and return lines for IP. no bubbles in inlet line. have 7-8 psi fuel pressure going into IP. return line gets bubbles in it when running, also when fuel shut solenoid shuts off to correct over speed blows bubbles back inlet hose. pulled intake to plenum off intake and hose connecting to turbo. oil residue in plenum and shining light into turbo housing oily. ran truck without plenum on intake and still surges. checked egr valve and not binding. put back together. still same problem. will try checking out all grounds tonight if time before work.

 

What did you find out?

 

Checked, cleaned and secure the grounds, replaced ground to engine that was rubbed almost through. Problem still persists. ordering new PMD. Any recommendations for best price on non- Chinese part? Will be relocating to some where other than top of intake manifold. Had truck running about 20 minutes checking for air bubbles, ss diesel heat sink and PMD sizzling HOT! This relocation spot seems to be no better than on the pump.

 

I would recommend leroydiesel.com for an extension harness and PMD.

He has Made in the USA PMD's and harnesses.

I have had better luck with the latest version Flight Systems PMD. I had 3 failed gray Standynes.

 

thanks for the recommendation. ordered flight system pmd and waiting on snail mail for delivery.

 

I got the Flight Systems PMD from leroydiesel.com, installed PMD and truck is back on the road. The grounds needed repaired anyway. I tried the PMD first, since it worked I'm now ordering the extension harness to relocate behind the front bumper. Thanks for the help.