2004 duramax rough idle?
 

I have a 2004 gmc duramax and when its at idle it seems to surge? anybody had this problem or no how to fix it?

Re: 2004 duramax rough idle?
 

2 different Duramax engines were offered that year.....
LB7....8th digit 1
LLY....8th digit 2

So whats the 8th digit in the VIN?

Re: 2004 duramax rough idle?
 

It's a lly
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Re: 2004 duramax rough idle?
 

If you dont have a scan tool....Have someone check....
1. Fuel Rail Pressure (FRP) sensor & connector.
Verify that actual vs desired fuel pressure match in scan data at low speed and under load and high speed.
Wiggle the FRP sensor connector while the truck is idling, check for RPM change, Replace the FRP sensor and pigtail connector if RPM change is noted.

2. Graph the input pattern (desired) for the fuel pressure regulator.
If the pattern has a saw-tooth appearance, replace the fuel pressure regulator.

I replace the FRP sensor, Pigtail connector &
Fuel Pressure Regulator. If I find ANY of the above.

Re: 2004 duramax rough idle?
 

generally that's a good sign the fuel pressure regulators bad

Re: 2004 duramax rough idle?
 

My brother in law's 04 (LLY) does this same thing..... surging at idle. I will pass this info along to him as well.