Help..Idle won't stabilize

[BDaugherty]

It's not a Cummins, but it is common rail with a CP3. My work truck is a '05 5500 Chevy with a Duramax. Recently, it has started to "lope" at idle. I does it most of the time, but not all. It's much more noticeable when the transmission is in gear and I'm sitting at a traffic light. The tach jumps between 550-700 RPM idle speed. It will continue to lope until the engine is really loaded. It has 81,000 miles on a stock fuel system. Also, in my business, 81K miles means a LOT of idle time running the PTO and such.

 

[Msilbernagel]

The most common causes I see when doing a search are:

FCA - fuel control actuator (gizmo on the CP3 controlling fuel in)
Injectors - evidently, they do go bad and the leaks can cause the surge. .

Try seaching the 3G forum for FCA and/or surge.

Good luck.

Mark

 

[BDaugherty]

I was thinking FCA, but I was hoping to get some feedback from those more experienced with common rail systems.

 

[SierraRam]

The FCA on my 03 started acting up amd had the same symptoms. Easy to replace.

 

[BDaugherty]

Update: I have now discovered that the engine surging is directly related to the turn signals. It's almost like the added load on the alternator is loading and unloading the engine each time the blinker flashes. I guess the next step is to run the truck with a meter connected to the alternator output and watch to see what it does at idle with and without the blinkers.

 

[Msilbernagel]

Check the voltage at idle - perhaps you have a diode out, and that output of the alternator is diminished, along with a lot of A/C noise.

It should be somewhere around 13. 5 or more; if 12. 6 or less, you've a charging system / battery problem. Check your battery cables too. .

Mark