Esp when under load , feels like eng miss , no codes , im a ford tech by trade so im thinking maybe a coil pack going bad ,what is the correct way to test gmc coil packs and are there any other things to look for shouldnt it be throwing a code obd2 cant find 5500 on list so i put closest vehichal i could find thanks forvyour help
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If it is a serious miss, you should have a code in the computer telling you which cylinder. If you have replaced the ignition parts and there are no vac leaks, the next phase would be fuel including the injector.
things that can cause it to miss.
fouled plug (checked)
ignition signal to coil pack( switch old coil pack to a working cylinder to make sure its good and you may find a possible short in the wiring to the coil pack) alternately check the voltage to the wires going to the coils make sure like colors have like voltages. im not too big into ford trucks but thats a good start for most vehicles
possibly injector stuck open and flooding cylinders
timing could be off
I THINK I UNDERSTAND THE SKIP UNDER LOAD,LOL,BUT THIS CAR DOES NOT HAVE WIRES,IT HAS BOOTS,UNDER THE COIL PACKS,AND I HATE TO TELL YOU THIS,BUT,IF IT IS A 4.6 LITER,THEN,FUEL RAIL HAS TO BE LIFTED,GOOD LUCK
I replaced the coil pack to no avail. I also purchase a code reader while at the auto parts store. This device told me cylinder 3 was misfiring (P0303). I found that the spark plug wire had shorted out on the manifold sensor tubes. Replaced that wire and done.
I highly recommend keeping a code reader in your car tool kit. very useful.
I too have that problem. I own a 2005 GMC Yukon. Shutters between 40 + 55 mph. I thought for sure the stumble I felt was a plug or coil pack because it only does it under a load. With A/C on the whole truck shakes! But it wasnt the plugs or coil packs. Answers anyone?