Duramax Head Gasket Replacement

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I'd bet most Duramax owners (who have looked at fuel rates) have seen injector balance rates that were better than the above image. Ideally, we'd like the balance rates to be all nearer to zero - or at least below 1.0. The above image was taken in the summer of 2021 soon after completing the head gasket and injector replacement project in my 2001 GMC crew cab. As some of you may recall, I installed brand new SAC injectors. I have to say that I was a little disappointed to see four of the numbers as high as they are shown here (cyl 1, 2, 6 & 8 ??) with zero miles on the new parts.

I recognize that many factors can affect balance rates - such as engine mechanical parts and of course injector uniformity. Things like uniformity in cylinder compression and uniformity in valve clearances can affect injector balance rates, and these are just a couple of the factors I've considered. Then, there's always the possibility for contaminating critical parts during the reassembly. I'm pretty good at keeping things clean, and I am not afraid to use/begin with a power washer, brake cleaner, clean shop towels, powerful shop vac, and beginning important work with a clean shop. I trust my work more than anyone else's to keep things clean. But, the above image did haunt me. I always use fuel treatment - injector cleaner, lube, cetane, etc. I had hoped that with time and miles, the injectors would "settle in". They didn't...

Over the past few months, I've noticed a bit more roughness in the engine when cold. I know that the automatic fuel-rate balancing doesn't begin till the engine has reached at least 100 degrees (IIRC). The engine did smooth out some when it reached operating temp, when the programming began to balance the fuel-rates. But, it never got to what I would call smooth...

About 10 days or so ago I noticed the exhaust would produce a bluish/white exhaust color (quite pronounced) when lightly accelerating, even at operating temperature. It would slowly go away, and then the exhaust would look more or less normal (clean). But the exhaust color would come back if (for example) you stopped at a stoplight, then pulled away. I noticed that what symptoms I'm discussing here had somewhat deteriorated over this past year... Then, a few days ago I pulled out my Predator programmer and looked at the injector balance rates again...



This is what I saw... The engine was at operating temp when these numbers were taken. They're awful. But if we can assume the "12.82" number is #7, it would be logical to assume that that high positive value is causing all of the others (except 2??) to go negative to compensate. If #7 was where it was when first installed, the numbers might be closer to where they had been originally.

Or, I could be thinking about this backwards... Maybe the 12+ for #7 is an attempt to compensate for an imbalance... I'll try to get the commanded fuel pulse width data as Greg mentioned in a PM to me.



Before unplugging the Predator, I looked to see if any trouble codes were present. The truck wasn't showing a Service Engine Soon light, but... sure enough, it had a P0307 in memory "#7 Misfire Detected", which sets when the injector fuel rate for one or more injectors is/are outside tolerance.

As you may recall, I installed a set of SAC injectors instead of the OE VCO injectors... SAC type injectors are advertised to produce a longer life when compared to the original factory VCO type injectors. As of today, these injectors have just 18,000 miles on them. The engine's original factory-installed VCO injectors were replaced with 120,000 miles on them...

All this was made more apparent late last month when I pulled Lil Red out of storage for the first time this year. That engine runs incredibly smooth when cold and like butter when at op temp. As you may recall, I replaced the heads gaskets and resealed the injector cups in that engine a couple months after replacing the head gaskets in my 2001 GMC in 2021. I was careful with Lil Red's engine as well, to keep the fuel injection system clean and uncontaminated. Both trucks got a new Baldwin fuel filter during the process.

So, what do we have here? Were the SAC injectors a wrong choice? Or, is something else going on?

Jim

https://www.ebay.com/sch/i.html?_nkw...023.m570.l1313

Repair possibilities:
1- Get a set of eBay nozzles/pintles along with the special tools, and see how it goes... LB7 nozzles/pintles are going for about $45 for each injector or $360/set of eight.

2- 8X Genuine BOSCH OEM Fuel Injector 0445120008 For 2001-2004 Duramax LB7 6.6L Brand New for $749

Last option... pay another $2400...