Duramax Head Gasket Replacement

[More Power]

The above code set a day or two ago. I cleared it, and the light remained off. Between the code indicating a problem with cylinder #7 and the latest balance rates below, I think we can can safely assume a problem exists with at least #7 (or maybe the whole lot of them...).



As others have pointed out here, a cylinder problem (compression, valve train, etc) has to be ruled out before assuming a problem with the injector(s). That's coming... I saw on YT that Harbor Freight sells a compression test set that includes a glow plug adapter for the Duramax.. for $30.

Has anyone seen more impressive balance rates?

[DmaxMaverick]

I'll wait for the GP visual and compression test. There's a piece of this puzzle missing, and I have nothing to add to the continuing saga. I still think that, if accurate, 2 adjacent cylinders increasing that much fuel, while the remainders are decreasing, adding in some smoke, indicates more than just an injector error or deficiency. Possibly a compression loss, of some sort. I do notice though, 14.16mm seems to be a balancing limit. An actual limit of fuel volume an injector is able to correct, or simply a display limit? I don't know, but it means something, even if irrelevant at this point. It's repeated enough to not be coincidental.

[More Power]

I'll wait for the GP visual and compression test. There's a piece of this puzzle missing, and I have nothing to add to the continuing saga. I still think that, if accurate, 2 adjacent cylinders increasing that much fuel, while the remainders are decreasing, adding in some smoke, indicates more than just an injector error or deficiency. Possibly a compression loss, of some sort. I do notice though, 14.16mm seems to be a balancing limit. An actual limit of fuel volume an injector is able to correct, or simply a display limit? I don't know, but it means something, even if irrelevant at this point. It's repeated enough to not be coincidental.

With those numbers I'm amazed that more codes aren't continually being set. And, I agree that the coincidence of same reading of "14.16" on two cyls seems a bit odd to me as well - what are the odds. We should be thankful that good ole #3 is within spec, if only by a little... (that's a joke... )

I can't begin the process of taking things apart till we get the Blazer sorted. There's only so much room in the garage... Hoping to get a callback from a local auto salvage yard today about a good used hatch and end-gate. Get those on, and then the Blazer can sit outside.

[More Power]

Slowly moving forward! I recently bought this Harbor Freight diesel compression tester for about $100.

Aside from simply a bad injector, an out of spec injector fuel rate balance could be caused by either a mechanical problem with the engine or an electric problem that affects the injector, such a broken wire related to the injector harness, an injector harness connection at an injector(s) or the FICM. A mechanical problem that affects cylinder compression could include bad pistons, rings, or valves (clearance(s), possibly due to an assembly error or valve train failure) or a timing problem. Any of which could affect cylinder balance. For any of these problems, the out-of-spec injector balance rates might be reflective instead of causative. The only way to narrow the source of the problem is to perform a cylinder compression test - all eight cylinders - that'll either eliminate or point to an engine mechanical cause.

This is their Maddox Compression Tester kit produced for diesels. A diesel compression tester needs to include glow plug adapters and sometimes injector adapters. A diesel rated compression tester also needs to be able to measure higher cylinder pressures than a tester made for a gas engine.



A diesel engine can produce cylinder compression pressures at cranking speeds of up to about 400-psi where a gas engine typically tops out at about 150-psi. I'm also currently working on a motorcycle engine that has an oil usage problem, and I wanted to measure its compression pressures before I took it apart. Most Duramax diesels produce somewhere in the vicinity of about 350-psi at normal cranking speed. The 6.5L diesel produces pressures in about the same range of 300-400, depending on how many miles there might be on the engine.



Here is a chart, showing what each part of the kit is, suggesting what it might be used for. The various kit parts here will adapt to the 6.5L diesel glow plugs, the Duramax glow plugs, and the NGK spark plugs found in my Yamaha. My Yamaha produced pressures of about 150-psi, which is excellent. This suggests that the bike's oil use problem may be due to valve stem seals. I have new seals for the cyl head, but I won't be able to eliminate the possibility of carbon fouled piston oil-control rings without pulling the cylinders off.



My GMC will be tested this winter sometime. I'm looking forward to seeing where the problem lies with the way out of spec balance rates.

We've begun a video series for these topics. Have a look!



Next video in the series - R&R Head Gaskets: https://www.youtube.com/watch?v=QQ1D1FUk1zs