97 LX450 / backfire / at start up (2 Viewers)

[Jim S.]

After engine cycles a couple of times for oil pressure and initially fires I get a loud pop. Had a 0420 code and replaced O2 sensors. I haven't had the code for several hundred miles. Thinking something something is up with the Cats, They are original and the truck has 130,xxx + on it. Truck is supercharged but I don't see that as an issue. No smog requirements in my part of Arizona and I could try an after market Cat, however I don't want to start throwing money at parts without a definitive cause.

Thoughts and advice appreciated.
Jim

 

[ChaseTruck]

After engine cycles a couple of times for oil pressure and initially fires I get a loud pop. Had a 0420 code and replaced O2 sensors. I haven't had the code for several hundred miles. Thinking something something is up with the Cats, They are original and the truck has 130,xxx + on it. Truck is supercharged but I don't see that as an issue. No smog requirements in my part of Arizona and I could try an after market Cat, however I don't want to start throwing money at parts without a definitive cause.

Thoughts and advice appreciated.
Jim

Not sure I'd think of the cat(s) first hand; I'd suspect something like too much unburned fuel, which is then combusting either in the header or in the cat(s)?

 

[Jim S.]

Not sure I'd think of the cat(s) first hand; I'd suspect something like too much unburned fuel, which is then combusting either in the header or in the cat(s)?

I was thinking that too, Possible bad injector? Plug ,wires and distributor cap were replaced a couple of years back and we don't put a lot of miles on it.

 

[efjayatee]

Knock sensors

 

[MissahPapaJ]

Reset fuel trims if possible, or pull ECU fuse for a spell if you can’t using scan tool. Some will, some scan tools won’t. After that start it cold and watch the short term fuel trims and also the long term fuel trims and see if they’re happy. I suspect you’re running lean if you’re backfiring. Cats shouldn’t really be an issue my cats just passed CA smog with some of the best numbers I’ve seen on an old rig and they’re original with 195k on the clock. Does your super charger have a extra injector on it?