Low compression- please help - Chevy and GMC Duramax Diesel Forum
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post #1 of 5 (permalink) Old 11-21-2019, 11:13 PM Thread Starter
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Low compression- please help

I bought an ‘02 duramax with 220k miles. It had a fuel knock for who knows how long. I drove it for about 200 miles until this happened... I was going about 50mph and the fuel knock all of a sudden got EXTREMELY loud. I pulled over and parked it and blue smoke started pouring out of the exhaust. I shut it off, started it back up... still smoking. Decided to continue driving it home for another 30 miles. The noise quieted back down within a few minutes to its original knocking sound. The #8 injector balance rate was reading high (7.5). Decided to put new injectors in. With the new injectors in, the noise pretty much went away except you can hear a very slight knock... checked compression and it’s reading 200 in that one cylinder. Is it worth diving into and spending more money trying to save the engine? Or is there too much damage done? What could be damaged. Not sure if I should take my losses or try and repair it. Thank you!
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post #2 of 5 (permalink) Old 11-22-2019, 08:03 AM
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Sounds like you should pull the valve cover back off, pull that injector and use a borescope to check that cylinder. Probably washed that cylinder down and has some significant scoring on the walls being that it is that low on compression. Does it have a lot of blowby coming out of the pcv vent tube at the lower right front corner of the engine, or out the oil fill tube with the cap off?

It all depends how much money you want to spend on this truck. I mean, you're already into it for injectors now. You might be just as well off to buy a replacement engine and put your new injectors in it and go on. If the cylinder is scored and has to be machined, you'll be buying pistons; if you're buying pistons, you might as well buy rods; then you might as well buy some other goodies to go with all that and have some real fun with it. But, then again, if you're wanting it to be a work truck or just a dependable non-performance truck, that's probably not the best path to follow...

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post #3 of 5 (permalink) Old 11-23-2019, 01:58 AM Thread Starter
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Hey thank you! Yes, I do not want to spend a lot of money on this truck... I was trying to buy a low price diesel but was obviously a bad decision. So basically it’s going to be a lot to repair this engine...? Without even diving into it?
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post #4 of 5 (permalink) Old 11-23-2019, 05:30 AM
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If all the other cylinders have good or okay compression you could just try to clean that cylinder stick another piston in it and hope for the best. A full rebuild or picking up another engine is probabaly in order though like matt suggested.

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post #5 of 5 (permalink) Old 11-23-2019, 05:42 AM Thread Starter
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Okay. Thanks guys I appreciate the help
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