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Hello
I have a 2005 silverado 1500 4x4 I put a creat engine in . Now it has a misfire on #1 cylinder tried moving the coil ,plug and wire checked injector with noid light check compression at 175 installed new injector fuel trim at 25 so put a o2 in upstream now my short term is good but long still at 25 did water test for vacuum leak also smoke machine. spark plug black like rich .
Try a running compression test.
Start the engine with your gauge in the cylinder. Once it's running, press the relief valve to clear the cranking compression from the gauge, and see if it builds any compression when running.
I expect somewhere in the area of half the cranking compression.
I have seen GM lifters fail only when running, making good compression cranking but none at all (or sometes just uneven compression) while running.
If you have a scope and in cylinder transducer set up, you stand a better chance at catching uneven running compression, but if it's a dead miss (and if the lifter really is the problem), then the gauge should work.
