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Running Rough


Old 06-01-2010, 09:41 PM
Chuck0129 is offline
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Default Running Rough

Having trouble with my 06 cummins and need help figuring out.
The truck is running rough, smoking, pretty good knock, and every once in a while going down the highway it revs high until I put my foot into the accelerator and let off. I have changed the fuel filter and bled it several times. think maybe bad diesel but the reving up has me nervous. Any help would be greatly appreciated.

Last edited by Chuck0129; 06-01-2010 at 09:45 PM.
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Old 06-01-2010, 11:08 PM
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Usually a mixture of Gas in the diesel make a diesel engine rev up involuntarily, knock, and run rough but i'm sure this isnt the case. I would suspect the injectors or injector pump. I drove a cummins for my dad not to long ago and the injector pump was going out and it would rev up going down the road. It eventually didnt run anymore after a few days. But i hope your problem is just bad diesel.
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Old 06-01-2010, 11:10 PM
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I'll move this to the Cummins section for better results
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Old 06-02-2010, 07:58 AM
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Coal Train
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You've got one of two problems.

It's either 1 - the fuel control actuator (most likely, due to the revving up you're describing), or 2 - You have an injector sticking open.

Your best bet is the bring it to the dealer, have them hook it to the StarScan or StarMobile and do the following tests.

1 - Injector Kill Test. Shuts down individual injectors to find the one causing the smoke, rough idle, etc.

2 - Cylinder contribution test. This will tell you if you have an injector solenoid crapping out.

3 - You need to see the rail pressure. Both the requested pressure from the ECM and the actual pressure at the rail. This will tell you if the FCA is shot.
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Old 06-02-2010, 10:17 PM
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Coal Train is dead on. Have those tests run and let us know what the results are.
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Old 06-10-2010, 10:54 PM
Chuck0129 is offline
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Thanks for the help. Unfortunally I am dealing with the worst shop in the world. Not living close to a certified mechanic I had the truck towed about 60 miles to the dealer I bought it from. Their service advisor would not let me talk to the mechanic. Said he was to busy. Anyhow they reported that I had water and dirt in the fuel system. The dirt was causing the injectors to stick. They cleaned the system and told me to come pick up the truck. They told me it would take a little while for the rest of the water to go through the system. While driving the truck home it did perform better but ran rough at times and it did one time start revving again. This time it did not rev up as much as it just stayed where it was after I let off the accelerator. I put the truck in nuetral and pulled over. Kicked the pedal and it cleared up. I dont know if they fixed anything or not. I dont see why I would have to run excess water out of the system if they cleaned it out. Best I can tell by way of Hanes Manual everything gets purged during cleaning. Maybe it will be ok. Any experienced opinions would be greatly appreciated.
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Old 06-11-2010, 11:59 AM
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That revving is due to rail pressure staying elevated in the rail.

That is 100% the fuel control actuator.

If you go back to the dealer, ask if they have an actual diesel tech? Then, give me a call and put me on the phone with the guy so I can tell him what the hell he needs to do.

Most dealerships don't have a full time diesel tech and finding one the knows what the hell he's doing is even more difficult.

PM me if you need a phone number.

I'm tellin' ya, this is an easy fix that you can do your self. It's a 15 minute job to swap the FCA. It's 3 torx head bolts and 1 electrical connector.
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Old 06-13-2010, 11:42 PM
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Coal train could it possibly be the fuel rail pressure sensor? If it has a fault it will go to max fuel rail presure determinded by the ecm correct?
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Old 06-14-2010, 09:38 AM
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It could be, but not likely. That always sets a code.

There are a few things that can go bad and not set a code, they're all mechanical and aren't monitored by a sensor.

If the FCA fails mechanically, it won't set a code. If it fails electronically, it sets a code.

If the injectors fail below the solenoid, it won't set a code. If the solenoid fails, it sets a code.

Pretty much everything else in the fuel system is monitored electronically.

What you can do is pull the FCA out (very easy, just 3 torx head bolts) and shake it back and forth. If it rattles, it's good. If it doesn't rattle, it's stuck and needs to be replaced.

The injectors are a bit harder to see. You have to pull them out and inspect them under a magnifying glass (in most cases, unless it's REALLY catastrophic). What you normally see there is a crack in the injector body or the nozzle, usually both.

These pictures are tough to tell, but here is what you see when it's a cracked injector body and nozzle. Usaully you have to use a magnifying glass or you have to put the injector on the flow bench to see if it's cracked.

You can kind of see in the first picture where the body is cracked by the fuel passage (the hole at the 5 o'clock on the face).

In the second picture, you can see the discoloration by the hole that is also in the 5 o'clock position. You can't tell in this picture, but the face of that nozzle is actually spider webbed all the way across it. Much longer and that would have be a catastrophic failure resulting in a motor rebuild.

Normally, when this happens, it's accompanied by HUGE amounts of white smoke at idle and the idle is rough. It's easy to figure out with the StarScan, all you have to do is shut down the injectors until the one you shut down causes the smoke to stop and the idle to smooth out.

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Last edited by Coal Train; 06-14-2010 at 09:43 AM.
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