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1995 GMC Jimmy cylinder misfire

Anytime it rains my car has difficulty starting yet once it starts it runs rough for a while until it warms up and then runs fine. During one of these episodes the service engine soon light came on so I took it to a auto parts store that allows me to use a computer to read the codes. It indicated that there was a cyclinder misfire. I had the fuel filter replaced last summer and I also just recently cleaned the EGR valve however it has been 4 years since I had a tune-up. Why does this happen and What should I replace first? Spark plugs? Wires? Cap and rotor? Clogged fuel injector? Bad O2 sensor(s)?

Moisture and secondary ignition systems don’t mix. Replace the cap, rotor, wires, and plugs.


Thanks a lot.

Misfires get a heavy application of traditional, some might even say “tune-up style” fixes( since it is not common for your engine to have low compression I am comfortable leaving the compression check out of this list, but getting these numbers at some point will have value). I suggest a good look over of just where you are in the maintenance schedule you are for your car as this my be the piece of data that tips the scale as to the decision of if you should do something or replace something that could be considered “extra”. I am comfortable with using the term “tune-up” with a 1995, but just barely. It is possible your car uses electronic multi-port fuel injection (as opposed to the spyder and poppet valve CMFI system) as the “S” trucks started earlier with electronic multi-port fuel injection. Unless you post back that you actually do have a CMFI equipped truck we can stay with standard tune-up items (hold back on the 02 sensors for now).In addition I do accept the do it yourself fuel injection system cleaning (I prefer the pressurized can tapped into the F.I. loop in comparison to a simple addition to the gas tank contents. If F.I cleanings from the shop were not so expensive (70-100 seems to be the price) I would have this on a standard “to do” list.The F.I cleaning is one of the add ons that I like (as opposed to the extra internal engine cleaning products). The industry has the pricing structure of these additional services all wrong.