Expert: Robert Summers - 3/7/2008

Question
I own a 1995 gmc sonoma with the 2.2l 4 cyl motor. About 3 months ago it developed a low rpm miss that is noticable
when sitting at a light, but one you get to highway speeds(35 mph or higher) it goes away. I have replaced the plugs and wires 2 months ago and loomed all plug wires. I have checked for vaccum leaks as well, even took it to a mechanic friend of mine to hook up to the computer, but got no codes. Could it be a coil pack(truck has 2) or a fuel injector?? I also replaced the oxygen sensor. Any help here will be greatly appreciated.

Answer
Hi Gene... do you have a lab scope...use one to check the parade when hooked to the coils...sounds like a short to ground from a coil to me but a lab scope will tell you for sure...print off the parade from the scope and if you look on the internet for coil patterns you will find a good pattern to compare it to...an easy test is to wait till dark and spray coils with a light amount of water and see if you see spark to ground or hear a snapping sound of power to ground..if you do chances are that coil,(one or the other) is Bad... hope this helps