Hi all- new to this forum. I have a 98 GMC Z71 with the 5.7L in it. It throws a code that say's there is a misfire on the #5 Cylinder. I have replaced the cap, wire, plug, and fuel injector, and it still throws the code.
I purchased a noid light kit, and the ECM seems to be pulsing all injectors. No ideas left. Any help? (the truck has 197k on it, but otherwise runs great.)

 

here are some common causes of a misfire

Faulty spark plug or wire
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector
Burned exhaust valve
Faulty catalytic converter(s)
Running out of fuel
Poor compression
Defective computer

 

agree- but there are no other codes logged, but the misfire on 5. It may be possible for the ECM to not pulse the injector on just one cylinder some of the time. I would think that if it were any of the other causes, I would be seeing other codes also. It would be expensive to get another ECM just to try it. Do you know if the diagnostic readers that are used at Auto Zone are capable of reading all the codes?
Hate to take it to the dealer. (ouch!!)

 

they should read all of the codes. Have you asked them to reset the code for you to see if it comes back?

 

yes I have. I am going to switch the "new" plug from the #5 cyl. to the #1 cyl. Maybe a defective plug? Had it happen before. Also going to check the timing by going to TDC and make sure the rotor is pointing to #1. If that fails, I guess I will take it to a shop. Thanks for your help!! When I move on to the Wife's F250 (which
she just told me her service light is on) I may look to this site again. When it rains, it pours.