IIRC GM says that you check the injectors when the truck is at operating temperature. One reading in park, the other reading in drive at idle.

 

x2, should be at operating temp.

I had the same type of thing. Cold they would all read good, then when warm I had one that would go to +10. Eventually after a few more tests I decided to replace that injector and now all is good.

One other thing to consider though is a bad fpr has the potential to cause some unusual balance rates. My rates not only read high, but I could also hear it ticking, so this was enough to convince me it was the injector.

One other good bit of information when looking at injectors is positive rates means plugged injectors and negative rates mean leaky injectors.

 

Here's the procedure from GM:

1. Start and run the engine until the engine coolant temperature is more than 82°C (180°F).

2. Turn OFF all accessories (A/C etc).

3. Hold the brake pedal in the fully applied position. A hiss will be noticeable when the brake is fully applied.

4. Place the transmission in Drive.

5. Idle the engine for more than 30 seconds.

6. Record the Balancing Rate Cyl.1-8 parameters from the scan tool while the engine is at idle speed.

7. Repeat steps 2-6 with the transmission in Neutral.

Are all of the Balancing Rate parameters within the first specified range in Drive, and the second specified range in Neutral?


Specificed Range:

-6 mm³ and +6 mm³ - Drive Range

-4 mm³ and +4 mm³ - Neutral Range

 

okay, I will check and record the exact values later today with the truck warm, and them put them on here. There were one or two injectors that had values of 7-8mm³ in neutral when the truck was warm. I know one of them was injector #3.

All the rates where within their ranges when the truck was cool, but once it was warm a couple of the injectors where out of the range.

 

Okay, I just checked them with the warm engine.
With the truck in Neutral;
#1: 3.3
#2: -2.4
#3: 7.1
#4: -1.6
#5: -.2
#6: -2.9
#7: -2.4
#8: -.5

With truck in drive;
#1: 3.5
#2: -3.1
#3: 8.5
#4: -2.0
#5: -.2
#6: -2.8
#7: -2.7
#8: -1


What do you think about injector #3?

 

#3 definitely looks suspect. You also have a number of fairly high negative rates, could possibly be thrown off by the high positive though. I know they are still within GM spec, but would concern me. A couple things you can try is the DIY injector cleaner (has helped some improve their balance rates) and an injector return rate test.

 

I wouldn't put too much stock in the high negatives until you determine the cause of the injector #3 reading. If it was my truck, I'd replace the FPR first (based on the fact you mention there is some loping and you think its going), then recheck balance rates. If that injector is still reading similar, given your mileage, it's reasonable to suspect it may have an issue and I'd replace it.

 

X2

Run a ton of Diesel Kleen through then, replace FPR, recheck, replace #3 injector, recheck, etc

When they are all in good shape, typically none should be more than +/- 2.0 mm3 at idle (ideally less than +/- 1.0 mm3).
The GM spec is for warranty purposes, not to keep your truck in good shape or to get your best MPG.

 

I 2nd Maine Silverado's plan.

I have no FPR symptoms but had an injector at +8 or so, replaced it and it plus most of the others came back up with lower/better balance rates.

Good Luck

 

okay thanks for the input!!