Considering unplugging the coolant temp sensor eliminates the backfire miss stumble condition at cruise speeds I doubt the cat is the problem. Nearly certain its the O2 sensor, plan to get a new one installed this weekend.

 

OK so I let this repair slide for a while... Was still driving the truck some but not alot as I was using a diff vehicle for work. So I got a new O2 (bosch OE style from autozone) and installed it yesterday. Didn't drive the truck yesterday as I was possitive this would fix the problem. Decided to drive truck to work today and sure nough, damn thing is STILL backfiring. It was pretty cold this morning so took a while for warm enough to use the o2 and it was running fine then but once warm and o2 came into play bang bang bang... It does it at about 1600 to 2400 rpm's in any gear and at any speed at approx those RPM's while maintaining speed or at VERY SLIGHT accell or decell... A previous test of unplugging the coolant temp sensor (history above) resulted in the backfire problem going away so I KNOW it has something to do with open vs closed loop and highly probable is the o2 sensor. Guess now I suspect wiring of o2 circuit, how to test? Any other ideas that might cause this?

One other thing, I have a pretty bad hole in my muffler. Could this mess up the o2 reading? Seems the o2 is a LONG way from the muffler. o2 is at the Y pipe ahead of the cat converter and muffler is way at back of truck bed. I've been holding off on getting a new muffler until the backfire is resolved as I dont wanna blow out a brand new muffler with this problem but maybe the muffler IS the problem???

Any other ideas?

 

had the very same thing happen to me check your positive battery cable for breaks etc and also the small wire from the starter it sounds like you have a short

 

check the timing..sounds like a timing problem the computer controls the timing.

 

Have you found out what your problem is yet? I have the same problem and cant find it

 

Unfortunately no. I have not looked into the positive battery cable as suggested above and should do that. I'm also tempted to buy a new coolant temp sensor as with that unplugged the backfire goes away. I had done some simple testing of the temp sensor before but who knows... But that part is only like $12. I also need to investigate the wiring to the O2 sensor. As mentioned before, replacing the O2 sensor did not fix the problem.

 

To me it sounds like maybe the fuel sync is off a little bit. That could explain the backfiring, You might want to take it to a dealership and have them set the fuel sync. Have them check the fuel sync and reset it as necessary.

 

Have you checked your MAP sensor yet. I had a truck once that did this and I eventually tracked it down to a MAP sensor going bad.

 

O2 sensor or fuel pump my 92' Dakota 318 backfired with the same symptoms u r having sounds like a fuel problem to me not the computer

 

depends on if you have 2 o2 sensors