Hi All,
Engine is a 4.2L, 1999.
On the way to Lowes for some Formica for the build the van started running rough. The Scangauge shows both codes P0303 and P0304 which I believe is misfiring on #3 and #4. Before I start digging, any suggestion on what could cause them both to go bad at the same time?
Thanks,
Dave

 

They might not be both misfiring; my Excursion would show two misfire codes when only one was misfiring. Mine showed the cylinder that was misfiring as well as the next one in the firing order.

I'd start by seeing if you have a spark on those two cylinders.

 

Thanks for the help Tom. You were absolutely right. The problem was only with cylinder #4. The spark plug boot was just hanging there.





Nothing a new set of plug wires couldn't fix.