94' 5.8 Backfires
10-22-2017, 12:53 AM
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94' 5.8 Backfires
Hey guys posting this up for a family friend.
Truck is a 1990 f150 that originally came with a 5.0 and auto. Previous owner swapped in a 5.8 with a manual. Truck ran good for about 3 months after they bought it, and then after messing around while offroading(donuts in the dirt) the truck started backfiring. When I went to check it out for him it only seemed to backfire once the engine was at operating temps, and under load (Appeared to be coming from the driver side bank best I could tell). Didn't backfire at all when idling but he said it has in the past before (Said it sounded like a machine gun going off).
So far they have replaced the plugs, coil, distributor, fuel injectors, set the timing, TPS, 02, MAF, new smog pump. Ran a compression check and it was good too.
I don't think when the swap was done they changed the ECU's so I would say it still has the 5.0 ECU. With that said I did the paper clip trick and the computer said the TPS voltage out of range (Which I am not entirely sure about b/c they just replaced it and it runs fine until it get's warm and then starts backfiring under load). Also the check engine light wasn't on either.
Not sure if the auto and manual ECU logic is different fueling maps and they just need the correct ECU (It apparently ran fine for 3 months before so I would think not)
Could a clogged cat cause this? Wonder if the ECU is giving me a legit code on the TPS voltage being out of range since it was 5.0 motor converted to a 5.8?
All input appreciated
Truck is a 1990 f150 that originally came with a 5.0 and auto. Previous owner swapped in a 5.8 with a manual. Truck ran good for about 3 months after they bought it, and then after messing around while offroading(donuts in the dirt) the truck started backfiring. When I went to check it out for him it only seemed to backfire once the engine was at operating temps, and under load (Appeared to be coming from the driver side bank best I could tell). Didn't backfire at all when idling but he said it has in the past before (Said it sounded like a machine gun going off).
So far they have replaced the plugs, coil, distributor, fuel injectors, set the timing, TPS, 02, MAF, new smog pump. Ran a compression check and it was good too.
I don't think when the swap was done they changed the ECU's so I would say it still has the 5.0 ECU. With that said I did the paper clip trick and the computer said the TPS voltage out of range (Which I am not entirely sure about b/c they just replaced it and it runs fine until it get's warm and then starts backfiring under load). Also the check engine light wasn't on either.
Not sure if the auto and manual ECU logic is different fueling maps and they just need the correct ECU (It apparently ran fine for 3 months before so I would think not)
Could a clogged cat cause this? Wonder if the ECU is giving me a legit code on the TPS voltage being out of range since it was 5.0 motor converted to a 5.8?
All input appreciated
Last edited by turboman1; 10-22-2017 at 12:59 AM.
