1993 8.3, rear engine pusher. Engine pulsates throughout the engine running ranges. Well maintained fuel filters etc., includes changing the lift pump and blowing through the return line back to the fuel tank making sure there wer no obstructions. Engine does not smoke. Low end take off is getting worse. I think that the turbo is going south. Has anyone else ran into these issues? I don't care to try a few things with tweeking the pump yet I need to try and figure out what fuel pressures off the lift pump and at the injection pump I should have and exactly where I can test the turbo. I will look at a couple Cummins books and see what I can find. I usually have better luck and advice with these forums. I have 25 years experience in automotive, hold two ase master certs and can try some things without getting myself in too much trouble. Any help is appreciated and I hope I can return the favor here in the future. We work with a fleet of school buses so we usually don"t have any major issues. OH, I rebuild a few automatic transmissions here and there and a few engines now and again. Most of my rebuilds I do at the home shop as side jobs. I'll try to help you folks when I can. I don't know it all but I try.

 

is it hard to start?

 

No. Fires right off with no problem. I don't think I have a fuel return issue yet. I will drive the bus down the highway and hold a constant pedal position and you can feel and here a slight speed up and slow down of the engine. Pulling out into traffic, you need to make sure you have enough time. It has what I term a "dead spot" like an old carb gas engine does. You know, step down on the pedal to the floor take off and the gas engine falls on it's nose like the accellerator pump isn't squirting any gas in the carb the instant the plates open up. Then it will slowly pick up speed. Slowly!

Just so you have all the facts, I had added stop leak sometime back to address a slight external, rear of the head, head gasket seapage leak. The leak stopped. Engine has just over 100,000 miles on it and again has been well maintained as far as filter changes and services.

We had replaced the air throttle actuator and it made no difference. The original one had air bubbles all over it when we sprayed a soap water solution on the lines. We thought we found the problem. The rod moves freely and doesn't hang up. When the vehicle has the air brake parking set and in neutral, one of us does the foot pedal up front and we watch the rod. Moves instantly and doesn't hesitate at all. Tight on the injection pump shaft. Engine sounds real healthy during this inspection. get it out of the shop on the large test parking lot or open road and you get the variation pulsation of the engine rpm drops and climbs, drops and climbs, and rarely steady like it once was. Less noticable at top highway speed yet you can tell. Kick this around in your heads for a day or two. I am going to try and access the turbo vanes just to see what shape they are in. Will drop the large air filter just to see if there is something going on there.

Thanks for reply. Will check back later.