Injectors

[ADub]

Truck has 73k on it. #7 injector balance rate has been hanging just under 4mm for the last couple weeks. Took a 1500 mile trip last weekend, pulled a car back. Got 20 mpg empty and mileage has gone way done since I returned. Balance rate on #7 was 5.6mm at the end of the trip. Im getting under 15 on this tank and its half highway. I typically get 17-18 around town. Checked the balance rates and #1 and #8 are in the 2's and #7 is less than 1mm. I only refuled at major stations, but the only thing I can think is the fuel filter, unless there is something about the balance rates that I don't understand. All the balance rates were checked in park.

[Kennedy]

Sometimes additives can help bring them back in line also depending on what the issue is. Also, I'd suggest verifying balance rates with a Tech 2 if you are using a generic tool.

I run FPPF Total Power in all of my diesels, and have added filtration also.

[ADub]

Makes sense, I did run Stanadyne on 2 of the tanks during the trip. I checked the rates with a Predator. On a side note, I noticed a 1.5 mpg decrease with the 40hp Predator tune on stock tires. 315's didn't seem to make much of a difference. I'll put it back to stock on this next tank and see what happens.

[ADub]

#7 balance rate is back to 4.5-5.0 mm range in park. Do I need to wait until it goes completely, or will a dealer be willing to fix it now.

[DmaxMaverick]

There's a lot more to bad injectors than balance rates. A correlating PWM spike/drop is one. The dealer will/should also check the return rates, which is the #1 indicator for replacement.

I recently had all my injectors replaced. The balance rates I tracked with the Predator were in line with the dealer's diag. The return rates and other parameters were the "deciding factor" for the replacement. The balance rates, according to GM, can be as high/low as 9 before they take it serious. The cylinder balancing is a normal process to offset manufacturing variations.

A good test you can do yourself to check the actual balance condition is to check at idle with balancing on and off. With engine idling and warm, watch your Predator balance rates. When they all show a balance value, and PWM also shows a value, the engine is in balance mode. If you depress the go pedal, just enough to get it out of balance mode, but not enough to increase engine RPM, the injectors should be firing at the default volume, PWM. You may notice a slight change in RPM fluctuation and/or smoothness. A little change is normal. If it is a big difference, your dealer will see it on the Tech II, and should replace your injectors for that reason alone. In my case, the engine would transition from relatively smooth to loping like a BBC with a serious cam.

Also, I didn't have any fuel in my oil until after the injector replacement. A return line didn't seal properly and filled my crankcase within 20 miles of getting it back. All better now. It took longer to get the return lines (he replaced both) than it did the injectors.

[ADub]

Whats PWM?

[ADub]

I performed the test you described. Noticed little or no change in the PWM numbers, but the idle got rougher, not as bad as you described though.

[Kennedy]

Originally posted by ADub:
#7 balance rate is back to 4.5-5.0 mm range in park. Do I need to wait until it goes completely, or will a dealer be willing to fix it now. If you can find someone with a Tech 2 to check the injectors would be best. I've seen them show high on the Pred and much better on the Tech 2.

Also, I always check hot and in Neutral. Readings will stabilize as the idle time runs as the balancing shuts off as soon as you move the accel pedal.

[DmaxMaverick]

Originally posted by ADub:
Whats PWM? Pulse Width Modulation

[ADub]

Guess I should just wait till the injectors go or the PWM test gets more violent

[DmaxMaverick]

Originally posted by ADub:
Guess I should just wait till the injectors go or the PWM test gets more violent Wait 'til they go, it's to your advantage. The longer they work well, the longer Duramax has to make improvements on the injectors. Ideally, they would quit at 199,000 miles. Mine were done at 86K, so the campaign doesn't apply to me anymore (or anyone that's had them replaced under the extended policy). Any problem will be a new problem, and they won't replace all 8 under the same policy.

If you look for problems, you will find them. Whether they exist, or not.