I own a 1997 Ram 1500. it has the 318 in it, and the check engine light has been on since i bought it (cylinder 5 misfire, says cat and 02 sensor). The light also flashes whenever it is floored. I have replaced all the wires, spark plugs, fuel injectors, and the upstream o2 sensor, but I keep getting a cyl. 5 misfire. I did a compression test and all cylinders are the same. ive unplugged the cyl. 5 fuel injector while running, and get no change in rpms. also unplugged spark plug wire, and it is getting spark. any ideas as to what the problem is?

 

I can bet my pay check that you have a bad cat. That would explain the misfire and the fact that when you punch it, the CEL flashes. Shake you cat and see if you hear something rattles. If so, then that means that your cat is plugged and not allowing you engine to breath. Essentially suffocating it.

 

Alright i'll check! But would that cause only 1 cylinder to misfire?

 

Not necessarily, usually when a cat goes bad, it is the rear two cylinders that misfire. But yes it does sound like you have a bad cat. Straight pipe it or run a high-performance cat

 

yea that what it sounds like to me also

 

when cyl #5 injector is unplugged, do you get an increase in the miss?
if not, then the injector might be bad.

with truck off and injector unplugged, test resistance across the pins with an ohm meter. i'm not sure what its supposed to be, but compare to the others.