YEAR, and ENGINE would help!

what brand plugs

 

your backfire is typicaly going to be a mecanical failure or a timing problem. its pretty clear that if your problem is still unchanged with the parts you put on so, it would be perfectly reasonable to rule out all repairs you have done and now to question the quality of them. start over from the start with simple diag, is backfiring out the intake or exhaust, under what throutle position, does it idle, how often does it backfire and at what rpm?

 

Whoever told you BOSCH plugs was OEM LIED!

I'm surprised you didn't have trouble with them long ago.

Look at your underhood label to see what the factory used.

 

Mark the calender, Don agrees with Rich!

Pretty safe bet it is some sort of Cherokee. Guess he said he has more than one 02 sensor, so he's Not Renix, and not 99-02, probably not Diesel or 4cyl.... I'm gonna guess a 91 to 98 4.0 with an automatic? (just a probability stab at the trans). Oh..the problem...I forget....

 

Dt>, pretty sure the down-stream 02 doesn't affect the running, it's just a smog thing. That said, it's sensor feed, and heater power might be shared with something that maters, but it's input can only signal a cat problem...I think.

 

Do you have any codes and what cylinders are misfiring