Questiongetting a "P0303" engine code - #3 cylinder missfire. 98 GMC 5.0 engine - manua tranny. Here is what I've done so far,
Replaced
plugs, plug wires,distributor cap,rotor cap,Took coil & module to "Auto Zone" for them to check out. Didn't have either tester for my parts to see if ok. Asked them to pull a new coil off the shelf. My coil & the shelf coil had the same "Primary & Secondary Coil " readings.
Replaced module - since my coil seemed ok and they couldn't test the module
fuel pressure regulator - guy up the service station thought it might be leaking by. Running rough. Sprayed starting fluid around - looking for a leak. Couldn't find one. Still had a P0303 code- engine running a little rough when 1st starts up. Smooths out pretty much when engine is fully warmed up.
Replaced just the #3 sparkplug. Found old one gapped @ .030. Truck started/ran great - cleared engine code
re-gapped all the plugs to right gap. Autozone told me .030. Should of been .060 like written under the hood. Trucked idled smooth as glass. Drove truck for about 15-20 miles no problem
Started truck up next morning, check engine light on with a "P0303" engine code - #3 cylinder missfire $#@*&%!
looking for ideas - #3 fuel injector? Lower intake gasket? Running out of guesses!
Bill
Answerthat misfire is causing the plug to regap i'm sure if you take that plug out you will find it not gapped properly again.. i had this same issue and i have to remove all plugs every week for about 3 weeks and sand them dry them and regap them. did that plug break when you took the old one out at anytime to replace it?
that cylinder is running lean possibly getting air maybe
you would have to clean the threads where the plug goes into and the plug make sure they are dry and regap it and put it back
when mine wouldnt stop i got mad and took it out to a country road and ran it wide open for a couple of miles and that fixed my issue of the wet plugs and such mine was a car but a gm car
