I have a 2004.5 48RE 2500 325 Hp Dodge that is stock with 160K. The problem is I can rev the engine and when I let off the throttle the engine RMPs come down in steps. 2000 for 2 seconds, then falls to 1600 for 2 seconds then falls to 1300 for 2 seconds and so on until it gets to idle. In the search for the problem it has been on the computer at the local Cummins shop. Injector cut out and contribution test are all good. When you let off the throttle you can watch the TPS fall back to idle but the motor stays reved up. No codes at all. We have replaced the TPS or APPS if you call it that, the FCV on the pump and it got a new Air Dog Raptor just because it was about time. No low fuel pressure problems were going on. Also going down the road it will some times have a little surge to it and at idle you can sometimes hear a little injector rattle that is what I would call excess. I am a road truck mechanic and if I were to guess it sounds like the Fuel Rail has two much pressure? The return fuel line is not restricted as that has been checked. The only thing that really grabs me is I can rev the truck up and unplug the TPS and the idle falls back to normal just smooth as silk just like I want it to but when I plug the TPS back in and rev it the RPMs again come down in steps. I have one guy in my shop that thinks injectors, one that says CP3 and a wife that s loosing humor if you know what I mean. I am thinking a wiring issue but who knows. Thanks for whatever help you can give and have a good one.

 

I believe the APPS has to be calibrated when replaced....was this done to yours?

For some reason that was the 1st thing that popped into my mind.

 

Yes it has, we have even tryed a second TPS thinking the first new one was junk with no luck.... Thanks and much thanks for the tip. I will take whatever I can get at this point...

 

A guy that runs an independent shop here in town once told me that anytime he works on a common rail, the first thing he does is rap the go-pedal a few times to see if the rpm's hang....he said most times that it does happen, like your case, it is an injector problem.

I don't know first hand so I can't confirm this info, but it is a thought. I know you mentioned they were tested but it could be something internal with the stix.

 

Good point. I wondered the same thing but when I unplug the TPS the problem goes away so.....I am pulling my hair on this one.

 

Do you have a chip on the engine...if so return everything to stock setting and try that.

 

Any codes? Have you hooked up a rail pressure gauge?

 

Sounds about normal. My truck has done it since 17,000 miles on it when i got it. Just drive it. It takes a while to blead off the excess pressure in the rail. A box will intensify this issue and make it more noticable. May want to check the FCA on the cp3. Run a little 2 stroke ashless oil in the fuel and see if it makes any difference.