'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: