Hello guys, new to this thread for one sole purpose (problem) actually. my 2000 cummins with 300000 miles still going strong, but dad's 2004 has been in the shop and everywhere else with no luck. Here's the problem-truck has 120000 miles on it and overnight it decided NOT to idle back down as usual. dealer says sensors, replaced them, no change. then dealer says they have talked to some experts(bullsh@t) and the truck needs a new torque converter. new converter installed, NO CHANGE. truck still seems like a sticking accelerator cable if that makes any sense. now dad grabs the so-called mechanic and asks him why the pre-heat light stays on now. The mechanic gives up at the dealership and says we can't fix the idle problem,(duh) and doesn't know why the light stays on. I started checking wiring yesterday, and the relay in the fusebox under hood is functioning and hot-wiring seleniods proves preheater is working, just no signal coming through the wires to activate seleniods. anybody have any idea as to why truck stays idled up? Just for the record, i work on heavy equipment but this problem is driving us nuts. thanks

 

Explain the idled up a little better. If you stomp the pedal and it revs up and stays there for a few seconds it's normal! If it's something else give Todd at T&C Diesel a call just google him! Wealth of info on Fuel systems!

 

what you need is a scan tool. what is the apps reading at idle? and how high is the idle? park and nuetral or only in gear? if its only in gear ive sen torque convertor begin tocome apart kinda like a clutch partially engaged when in gear it begins to drag rpm down so pcm ups fca duty cycle and injector pulsewidth to bring back to about 750 rpm, so truck wants to pull hard at idle. if it does it in park or neutral look at the apps 1 and 2. if voltage is above .7v on one and below 4.3v on 2 at idle check for a wiring short to voltage. if no short is found then its time to get into your back pocket bc its likely a pcm. ive only seen it twice but it can happen the pcm shorts internally sending 5v to the apps return circuit so when starting it would crank then run wide open. give some more info and ill see if i can give you a little more insight. im a dodge/cummins level 4 tech so im not blowing smoke up your ***

 

thanks for the info. started tracing pre-heater light yesterday,truck was running, then died. seemed like no fuel, but haven't had a chance to dig into it yet. scan tool shows no codes, and the truck stays idled up after you hit the accelerator for probably 30-45 seconds, regardless if its in park, nuetral, OR DRIVING which gets kind of interesting after passing somebody. have worked on cummins in our big rigs, on chippers, and marine applications but this thing is starting to p@ss me off. thanks everybody for the help.

 

It takes a few seconds for the rail to drain hense the rpms not dropping immediately. It's just the way the common rail is. If it's more than 4 or 5 seconds there is a problem probably with the PRV.

 

thanks for the info. problem is this thing started doing this overnight, and it's more than fuel staying in the rail.as mentioned, this truck had been to the dealer for this problem, they say they changed a few sensors(no evidence of this) changed the torque converter, (no they did not) but the truck is worse now than before the dealership worked on it.

 

Talk to Todd at T&C diesel!

 

4 to 5 seconds is entirely too long if im understanding correctly you are holding rail pressure after throttle release. the prv is just that it releases pressure when it gets too high, its spring loaded so it only pops at 26000 or so. thats not your prob and being that ive only put 2 on in six years to cure a prob your on the wrong track. get a fca fuel control actuator and stick it in the injection pump, its the only part serviceable on a cp3 from the dealer. sounds like its hanging causing the pump to continue pumping fuel into rail. feel pretty good that is gonna solve your issue. just make sure your fuel is clean bc if not it will do the same thing shortly. lemme know if that takes care of your issue. if not pm me back and ill get some more detailed info