This question is for all the duramax diesel experts out there. I have a 2001 Duramax, no mods other than exhaust and bigger tires. Lately, I've had a rough idle and reduced power. Using the predator, I check the balance rates and get something like this at park at operating temp:

1 -1.88
2 +3.94
3 +4.54
4 +.88
5 -3.02
6 +1.15
7 +11.16
8 -1.02

I've verified this for three weeks. I decide to call the dealer, who replaces the fuel filter (warranty), and I also decide to do a oil change. Guess what happens? The **&(*^^%^%#%@ balance rates go back to this, in park and at operating temperature:

1 +1.05
2 -1.44
3 +3.54
4 -1.75
5 +1.55
6 +1.21
7 -1.08
8 -.54

Everything is flipping identical except the new fuel filter, and the replacement of my oil (Rotella Synthetic 5W-40) with AC-Delco regular Dino and a new oil filter. Oil pressure changes from 55# to 60#.

My question is this. Are the injectors fired by the high pressure oil? If so, would using synthetic cause problems because of different viscosity? Or is there diesel in the fuel, causing a lack of viscosity so the injectors aren't firing properly.

The isuue I'm facing is should I pursue having the injectors checked, as now the balance rates are in spec at operating temperature?

I'm sure one of the experts will chime in here but I think the rates need to be checked with the truck in drive. Did you have the dealer check them while they had it?

I believe the procedure is to check the balance rates in both drive and park.

There is an update to this. I forgot that the oil was cold from just being put into the truck. The temperature sensor measures water temp, not oil temp. Now this afternoon, after driving about 10 miles in traffic, and getting both the oil and the water up to temp, my balance rates are as follows, in Park with a ECT of 192 degrees:

1 +1.24
2 -1.08
3 -3.58
4 -2.56
5 +3.25
6 -1.88
7 +8.56
8 +.088

Anyway, so I still have problem balance rates, I'm just curious about why they changed by 25% just by changing the oil and fuel filter? Also, looking at the data from the fuel tank, my fuel temperature was 165 degrees? Is that normal with 95 degree outside air? The specific heat of diesel is pretty high. It warms faster than water, but it shouldn't warm that fast unless hot diesel is coming back from the injectors?

Anyway, I'm taking it to the dealers on Thursday, wish me luck on these stupid injectors.