2001 Chevy Tahoe 5.3 No Spark In 3 Cyl.

Here are more updates guys!

this is capture a waveform of the ripple

And this is a capture of the YEL=CKP GREEN=CMP BLUE= INJ5 RED=INJ8

Here's a closer look of the waveform CKP - CMP - INJ5 - INJ8


Today i noticed that the COIL5 fires a few times on the initial turn on like i mentioned before but after 45 sec. to 1min of the engine is running the COIL5 starts firing again but the spark is way to weak. I checked 7 and 8 but no spark at all ..

i'm going to check it again from the basic again i think i'm missing something or a didn't check something right ..

When you unplugged the alternator, did you happen to get spark back on the misfiring cylinders? That ripple doesn't look too bad, but it sure seems like things run better with the alternator out of the picture...

Those injector captures are interesting... during cranking, it looks like #5 and #8 are group fired? But when running, it seems like #8 loses injection pulse, while #5 keeps firing. :huh:

actually the INJ#8 is the one keeps firing!
and the COIL#5 fires to times on initial turn on and then after a minute o so starts firing again but the SPARK is too week!
BTW no SPARK at all on CYL 7 and 8, and no INJ pulse on 7 at all.