B20b swap ej6 sedan misfiring need help!

Ok so i have a 99 ej6 sedan. I swapped a jdm b20b (non vtec). Long story short i put the swap (originally did it in a 98 ej6) everthing went fine and how i planned. Ran fine. Got it tuned on chrome bone stock only modification it had was a h22 throttle body. Bone stock other then that with a 2.5 exhaust manga flow tip. Got into a car accident motor was still intact and no damaged. So i got the 99 and swapped it over and made the certain conversions as needed. Ecu is a p28 with a jumper harness. My issue now is that as i was driving the car on my break from work it was driving normal doing about 30 mph. Came to a slight hill and as i switched lanes and gave it some gas the car bogged down wanting to kinda die out. So i pull over check my wiring harness made sure everything was fine so i drove it back to work with the car wanting to bog out after 2.5k rpm. I got to work turned the car off then back on and its been back firing ever since. When i turn the car on it starts pretty fine. But it’s constantly backfiring and when i rev it she sputters and wont pass 3k half throttle full throttle she completely boggs and holds back. I hear backfiring out the exhaust and a pop/back fire out the intake manifold. Was told it can possibly be a bent valve but im really not sure. Firing order is spot on. New plugs wires cap and rotor. Fresh oil change. Any help is appreciated. Thanks in advance. Also new to the forums.

Motor ran perfect. Upon swapping the car. Only needed a tune on my p28 for the b20 base map. So i got the car tuned. No check engine code after. Got into the car accident and check engine light popped up. Scanned it code was 10 for the iat but its been burnt out in my ecu prior to tuning. Ran like a beautiful in the 98 and as well as the 99 up until now that this happened im planning going vtec but id like to find the issue first before dumping cash and something not needed. Thanks again.


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Did any of the grounds on the motor/chassis become damaged in the accident? Other than that with the info provided maybe the ecu chip dumped the program? Not unheard of but not common, what tune did you have in the obd1 ecu?

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The motor is in a new car now and all the grounds have been connected as should. Ecu was swapped out and i tried a bone stock p75 ecu and same symptoms happened. I know my way around honda and these motors but this honestly has my struck. Motor has new spark plugs new wires rotor and cap. Tune was doing just fine and i dont have a non vtec motor to even checl to see if it does the same problem. I can’t post a video for some reason of how the motor sounds when its running. She still starts and runs but only under partial throttle due to the constant backfire and bogging but i dont wanna risk damaging some else so its parked now for a like 2 months.


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Where was the car hit? Crank sensor maybe? I know obd1 uses the dizzy for that but have seen some obd2 have a seperate sensor behind the crank pulley. Sounds like it may come down to a wire in the harness pinched from the accident or a bad sensor. Do you have another map sensor you can swap and try?

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No the car the motor is in now hasn’t been crashed. Its got the original harness on the car. The 98 the got hit is long gone. Pulled the motor swapped it over to the 99 body and it was plug and play. Turned over ran good for id say a good month or two and then randomly one day on my break she started doing this problems. Which I’m completely lost about cause ive checked multiple culprits and everythings checks out. Only thing i can possibly think of is doing a compression test/leak down and see if i havent a bad (bent/burnt) valve.
Spark plugs/wires/internals- good
Firing order- good
Map/tps- good.
Ecu- good
Oil- good.
Also for another note I purchased the motor online with around “30k” miles. Not sure if it will add any info but motor should be good which its should its very healthy. Tune made 136 whp 125 lbs tq
When i first swapped the b20b it was in the 98. She ran fine only issues was it had a slight bogging issue which I didn’t like when i would full throttle i felt it needed to respond much better so i got it tuned. Two days after getting it tuned i got tboned and that was the end of the 98. Got me a 99 pulled the motor swapped the b20b and it was butter. Just until recently when i was driving on my break she just fell into this weird bogging/backfiring mode. I didnt swap the ecu out because i don’t feel theres a need to. Ive revised it multiple times and everything is intact no burnt or broken resistors or anything aside from the iat thats been like that forever now. The p75 is known to work properly and ran previously on a ls with no problems tried it out on my b20 same problem as the p28 with the tune so i know it cant be the ecu.
See the thing is i was working on it one day replacing the tps I believe and something shorted out (in the 98) and ended up blowing the iat sensor inside of my ecu this was longggg before i even got it tuned. The car was tuned with the iat being burnt out so im confused on why its even on if its marking a cel code if it was tuned that way. You know? But i have not checked the timing nor comression/leak down test due to not having the tools for it and not completely understanding how it works. so i dont want to be doing something and end up lost half way through and mess something up. And also sadly where i live we have VERY few people/shops that are reputable and trustworthy.

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