Holy crap, would love to see pics of this jeep's engine compartment. Honestly, I am not sure if you need 2 sensors. Never heard that you did but I'm not sure.

 

I don't know what the engine came out of or if the PCM can deal with two o2 sensors but I'd want one on each bank with true duals. I could be way off here but just say there was an issue on the passenger side bank of cylinders and the computer couldn't compensate for it. Again I may be wrong but with forced induction I'd be a little more concerned.

Good luck, I bet that thing will almost pull a wheelie.

 

No, you do not need 2 sensors. The ECM has no way to read and deal with 2 O2s anyways.

Is it backfiring through the exhaust? Or back up through the TB?

Also, are you sure it's backfiring? Or is it just "popping" a little bit during deceleration?

And if the old exhaust was super restrictive and the new exhaust is very open then its very possible youre running too rich.

 

No, you do not need 2 sensors. The ECM has no way to read and deal with 2 O2s anyways.

Is it backfiring through the exhaust? Or back up through the TB?

Also, are you sure it's backfiring? Or is it just "popping" a little bit during deceleration?

And if the old exhaust was super restrictive and the new exhaust is very open then its very possible youre running too rich.

This. It is only going to be able to adjust so much in the ecm. But it only needs to get a reading from one

 

Also is it tbi or tpi?

 

stock GM PCM or aftermarket like a megasquirt?

 

or did the muffler shop straight pipe it so its actually white trash pipes being racked

 

Sorry, The guy that built it said the engine came from a 1995 1 ton with a stock rebuild 8000 miles ago but the computer is a 1990.
There is no cross over or X pipe. The original single exhaust was 2" and the new duals are 2.5"
Yes, it is AGGRESSIVELY backfiring through the exhaust, one loud one every time you excellerate and then let of.
I don't know if it is stock GM PCM or aftermarket. How do I tell?
Is there any adjustment for rich/lean or is it all done automatically through the computer from the 02 sensor reading?

 

Let's see if I can add pictures.

I can't figure out your photo program here??? It says it automatically resizes picture but when I attach them it says they are too big. When I resize them they are tiny like this one.

If you are able to view my albums there are pictures of the engine and exterior.

 

Anything further?

 

I don't have anything to add really, but if you can I might have it put on a dyno and tuned just to be on the safe side.

Maybe I'm paranoid but with boost it doesn't have to be off a whole lot to cause problems.

Hopefully somebody who knows way more than me will see this soon.

 

Does it back fire under normal driving or just when you rev the engine? or I think someone else said this, is it just a loud rumbling noise and popping?

 

It only backfires AFTER I back of the gas from full throttle. It has nothing to do with regular driving or revving the engine in neutral.

 

What are you running for mufflers? You had a lit of restriction with the old system. I am not sysprised that it is doing it at wot. But are you sure it is a backfire? And not a rapid popping? If it was too rich it would have unburned fuel issue causing the backfire but that would have been noticed before the new exhaust. I think you are getting cackling

 

Not sure of what the mufflers are, one is the original one from the single exhaust and I guess a new matching one for the other side.
It is not cackling, when it backfires it sounds like a shotgun and I am surprised it has not blown a muffler apart.
No one has answered if there is and adjustment I can make in the fuel system?

 

If you don't even know what the computer in the truck is no you can't make an adjustment lol. The pcm will have Id numbers and if aftermarket by chance even a name and model on it. You could see if fuel pressure is tapering off or something but that's about it. Find out what the truck is running for a computer and then get someone to look at it ( probably not happening)and or get the software and data log to send it to the maybe 2 or 3 guys that still tune tbi. Unfortunately the ancient Gm stuff for a tbi isn't really all that popular anymore so it's not going to be fun.

The other thing is the O2 sensor is irrelevant and wide open throttle when you are getting the backfiring. Even if you are off of cruise rpm and on the throttle harder it still will just look at the preprogrammed tables for fueling. The narrow band O2 you have ( this is all assuming a stock Gm tbi computer) only cares about setting stoich at cruise, that's it. In truth the switch from single to duals shouldn't have done anything.. so there is probably more to this than suddenly incorrect fueling tables. The Whipples just had a generic chip for their setup so maybe the headers and now free flow duals was just enough to throw it off. Doubt it though.

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Thanks for the info.
I have had this to two local shops for this but neither of them had the correct diagnostics for this old set up and no one said anything about and aftermarket computer. The guy I bought this Jeep from said the computer was from a 1990 truck so I am assuming it is stock. I live in a small town.

 

You are on your own then. Dynamicefi is kind of neat for those old pcms. A proper cable for your obd port and winaldl will allow you to data log the truck.

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