'05 Cummins Rough Idle/Sporatic RPM's. NEED HELP!!!
 

OK, so here's what's happening on my buddy's truck. First off, the truck is an '05 Quad Cab 2500 5.9L Cummins with 108,000 miles. It has a 5" Turbo back and an Edge EZ (Edge EZ was unplugged, didn't change a thing). When he got it, he noticed the idle was almost loping. Once we put the 5" exhaust on it, it was really noticeable. When you press the accellerator pedal (once the truck is warmed up, or when it's cold), it will accelerate higher than you wanted it to, and then hang there, drop a little, hang at the new RPM, drop some more, sometimes actually accellerate a bit, sometimes not, and after about 7-15 seconds of bouncing around the RPM range, will return to idle and lope. Was told everything from a cracked rail to a bad over-pressure pop valve. We replaced the rail with a new valve and sensor. Replaced the Fuel Control Actuator (FCA). Didn't fix it. I figured maybe the Throttle Position Sensor, so I just replaced that (which is a new pedal and APPS, combined). Still climbs up to 3200-3300 RPM and takes a good while getting back down to idle. The Tach is working fine, follows the engine RPM's to a tee. But this thing has got me worried. If it was one bad injector, it wouldn't run the entire engine so roughly, I wouldn't think. No DTC's associated to this problem, and none showing. I'm thinking a bad electrical signal somewhere, but where? The PCM/ECM? The camshaft/crankshaft sensors? The injectors, themselves? Sometimes when it revs up to redline, and then cuts off sharply, a poof of white smoke comes out. I'm thinking that's just a symptom, not a cause of anything. Any engine would do that, I believe.

Help me fellow Diesel Bombers, you're my only Hope!!!:argh::argh::argh:

Nothing, eh? No one else knows a thing on here, eh? This is pretty disappointing. Would have thought SOMEONE could have come up with SOMETHING. I refuse to believe that I am the smart guy on this subject. I see where someone had something simular going wrong with their vehicle, and that the posting was removed because the problem was fixed. Isn't the point to list the fix on the post and leave it posted for the rest of us to see? Or is it just me........

Fuel Filter replaced recently ?

I would look into the Cam/Crank sensors. Should be a relatively cheap part that could fix the issue.

Fuel filter IS new. Thinking crank/cam sensors are next. Thanks for the inputs, need someone to come up with something profound, because this is boggling me!:c:

was the edge put on by your friend? I have have seen and had friends who bought trucks with the edge product installed and they act a little funky.


if there is no codes being thrown, I would have to think that it is the pcm, have it reflashed by the factory, it cost me 90.00 when I had it done.

This is a pretty common issue on the common rail Cummins engines. I had an identical experience on my 03. It ended up being the FPR or FCA Fuel Pressure Regulator or Fuel Control Actuator. Either way they are the same part. Dodge calls it and FCA and GM calls it an FPR on the Duramax CP3's.

There is a small spring and a check ball in there that gets stuck, basically what is happening is the CP3 is unable to regulate the amount of pressure that is being delivered to you fuel rail. It is supposed to regulate based off of throttle position and ECM voltage signal. But when things get gummed up in the FCA this regulation becomes sporadic.

Check on Ebay for a new FCA, I have bought several off of there for anywhere from $80-$180 but either way it will be way cheaper than $380 from the dealership. I hope this helps!:c:

Vinny, we already replaced the FCA, check original posting.:c:

Is the ball/spring inside the FCA, or something else that I should have seen inside the CP3 when the FCA was off?

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The Edge EZ was on it when he got it. He removed it shortly after noticing the problem, but it didn't fix it. That's a good call on the reflash, gonna give that a try after this cam/crank sensor is replaced. Thanks!:c:

Sorry bud, I was slammed at work today and Scott just told me there's a guy with a problem on Bombers so he gave me the basic run down and it sounded like FCA issues. Give me a shout if you have a minute and we can see if I can help! 208-777-1977

Tomorrow, about 1400 hrs North Pole, Alaska time, I should have his crank / cam sensor ($36.87) replaced and his PCM reflashed ($51.50). If that doesn't fix it, I believe I will take you up on that and I will call you, Vinny. My friend is deployed right now, and I'd love to get this fixed for him because it's his only vehicle and his wife has been driving it and is afraid it's going to blow up. It shouldn't cause any permanent damage, but the sooner it's fixed, the better!

Thanks, Vinny. By tomorrow I should have a word on this thing.

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UPDATE:

Well, the new Crankshaft / Camshaft Position Sensor did NOT do anything for it. The PCM Re-flash is scheduled for Wednesday. If this doesn't do it, I'm thinking of letting the dealership get a hold of it. But that's a lot of money for a guy that doesn't make much money (U.S. Army Soldier).

When I pulled the crank sensor out, I figured that it HAD to be it, that thing was just COVERED in black oil/dirt crap. But, nope, that didn't do it. So, I'm still open for suggestions! Anyone? Anyone?

Vinny, I may be calling you right after the PCM re-flash, but keeping my fingers cross and praying that that will do it! Thanks, guys! :c:

Alright, this is what the reflash said: The #4 injector is acting up. So, putting in a new injector should fix it, right? NOPE! A new reflash and a new #4 had it doing the same crap, however, it DOES idle a LITTLE smoother. A VERY little. Just how bad can an injector get before it throws a code? If he'd had the money, he would have replaced ALL of his injectors, but he's as poor as our national economy at this moment. What's next? Anyone?. Anyone? Vinny?

Vinny, I'm gonna either call you, or have him call you AFTER the Holiday. Happy Thanksgiving, everyone. Hard to be FULLY happy with a limping diesel!!! :argh::argh::argh:

Replace all the injectors, check the fuel pressure to make sure pump isn't crapping out. Could he of got a bad tank of fuel? Anything added to the fuel?

It's not bad fuel, been like this for months (multiple tanks through diferent stations). Nothing is added to his fuel (2 stroke oil, cleaner, cetane booster, etc.). And replacing ALL of his injectors is pretty much out of the question for a while, as he doesn't make that much money (E-5 Army Soldier). His Airdog 165 is sitting in my garage, gonna put that on maybe this long weekend. Would be awesome if THAT did it. If it doesn't, there's not much left to replace in the fuel system other than the CP3 pump, itself. FCA is new, already. Keep sending me ideas and y'alls knowledge, though. I / we need as much help as we can get!!!:tu:

What you can try is ohm testing the injector solenoids. Pretty easy to do :)

Unplug all the injector harness connectors
Remove the valve cover (be two pieces, black plastic box and an aluminum cover)
Remove the 2 nuts from each injector solenoid
Wipe the terminals clean and test each one (ohm meter as low as possible. 20 is good)
If they test more than 1.0 ohm, the injector is bad. .4 to .7 is preferred. :tu:

That's what I'm talking about, someone giving me some actual troubleshooting proceedures!!! Awesome, thanks! Gonna give that a shot tomorrow after all of this Thanksgivving turkey runs its' course! Thanks, Wild Bill!

The check is between the two terminals on the top of each injector, right? Not the wire harness itself? This is done with the engine off for sure. Is there a ohm number for checking the harness as well? If the Airdog doesn't fix it, it's GOTTA be electrical!

Well, the new Airdog II DF-165 didn't do anything for it, so it's not fuel pressure. We are still going to try the ohm check, Wild Bill. Thanks again for the troubleshooting info. That's always what I'm looking for! :c:

clean every ground connection on the truck you can find, the ECM's do all their switching on the ground side ,and a bad ground in one place will try to find a path somewhere else and cause problems on the way.

check compression

check valve lash

check push rods

does motor shake at low rpm's and smooth out at higher rpms? (keep in mind that it a diesel, yes it will shake but is it normal)

i would check injector returns, get a measuring cup or somthing else that has ml or cc units, you need to take the cp3 pump return line off at the pump then disconect it at the rubber hose after that reinstall the metal banjo line and bolt back into the pump and attach a hose to the end of it and route that hose to a empty container. Reach through the wheel well opening and disconnect the return line quick connect and attach another hose to the metal fitting that u removed the return line from and route that hose into your measuring cup, crank the truck over some until u get a little fuel dripping out into your cup. then start and run truck for one min. at idle you should have no more than 180ml/cc of fuel in cup after one min. if more then try retightening all 6 of the fuel tube nuts and re run test. I would say you wont have more than 180, probly will be 50 or 70 ml coming out if that is the case the truck will need new injectors minus the #4 you have already replaced. The fuel you collect out of the pump you can just pour out or back in the tank, if you want you can measure this amount and it should be less than 1000 ml/cc but a cp3 output test is more effective for checking the pump than checking its return flow, to run this test hook everything back up. unplug your fca disconect the pump feed line going to the rail and put a hose on the pump outlet and into your measuring cup, crank in 3 10 second intervals and you should have no less than 70ml if less and you are sure you have plenty of fuel entering pump then you need to replace the cp3