i put high flow cats on my truck and about a year later i was getting a misfire code, replaced cats with cutouts and the code went away (never thought about cats causing that until now) i was getting an o2 sensor code at the same time though

 

The passenger side O2 sensor has been replaced when I first noticed the misfire. Threw a code for that. The truck idles fine, not rough at all.

 

so it only does it when you drive it??? does it only do it at a certain rpm??

take them cats loose...

 

so when was the last time you changed the fuel filter? I bet you got a dirty injector in the 5 cyclinder and should have it cleaned. dirt has a way of getting into the injectors on these motors.

 

I cut the cats off and still have a misfire.

Dealer computer says P0300 code. Autozone's says P0305 code.

I switched the #5 injector with the #2 injector to check for that.

Engine stumbles worse around 2100 rpm but the miss is felt from idle to 6000.
The miss is intermediate and sometimes is quits the miss above 4000.

Cleaned the MAF and Throttle body today also.

 

Stock converter? this just started happening? If it sounds spark related, have you checked the coil pack harnesses? you dont have a spare set of coils or a friend that has some you can barrow?

 

I change the fuel filter about every 10,000. Changed it a couple of months ago.

Manual transmission so no convertor.

Yeah it just kind of started or at least became noticable.

I'll swap coil pack sides and see what happens then. Good idea.

I'm also thinking I'm going to pull the intake and put a new gasket in. It was last pulled when I replaced the knock sensors which was about 1.5 years ago.

Thanks for all the help!

 

Things I am thinking are.........

vacuum leak (intake gasket)
cracked porcelin on spark plug
water leak into cylinder

 

I've checked the spark plugs and have moved them around to see if my misfire changes cylinders but it doesn't. I would have thought a compression test would show high pressure if water was in the cylinder.

 

bad wiring connection on the coil or the injector.