I have a 1992 Eddie Bauer Bronco with a 351. When I start it up it idles rough. The rpms jump between 500 and 250 when idling in park. When I press on the gas in park it backfires. When I try to drive it it backfires and hesitates on acceleration. I have dual exhaust with no catalytic converter. I was told that Broncos have a sensor inside the catalytic converter and without it it can't run properly. Is this true? If not what is the problem. Any help would be appreciated.

 

Well the exhaust could be the origin of the problem. The reving sounds like an electronic malfunction. This could come from the computer trying to compensate or it could actaully be a bad component. My first question is do you have a check engine light showing? If not has the truck been tuned-up recently? I don't want sound remedial but start with the engine codes first. From there you can start narrowing things down. Hope I can help.

 

The Check Engine Light never comes on when it is running.

 

Did this happen as soon as changed the exhaust? If so, then it might make sense that has something to do with it. If not, then the codes are the way to go.

 

Have you done any other modifications(tune-up, plug wires)or anything else and this started to happen?

 

It got a tune up last september. The problem started when I drove home and the car hesitated when I pressed on the gas. It hesitated once then ran smoothly. The next morning i started it up and it was idling rough. I tried to drive it an it didnt accelerate smoothly. I then looked under the truck and saw that my catalytic converter and y-pipe was glowing orange. After that I had the duals put on.

 

Did you see the plugs. If your exhaust got that hot something internal to the engine could have gone. Have done a compression check? Or timing? There are still a few things to rule out before assuming the engine is damaged, so if you have a few more good back ground points like, the glowing exhaust and no check engine light maybe we can narrow things down. Good luck.

 

[updated:LAST EDITED ON 09-Apr-02 AT 02:12 PM (EST)]That engine should be fuel injected and controled by the computer unless severly modified. The computer requires input from at least one oxygen sensor, possibly more depending on the type of eec in it, in order to manage air to fuel ratio. If it was a lone oxygen sensor it would have been mounted before the cats in the y pipe. If it was more than one they would probably be before and after each cat. If the mechanic that did your dual exhaust did not fully understand how they worked he might have hooked them up incorrectly. THe lack of an error code from the pcm seems suspicious all by itself given how the truck is running and would seem to indicate they are working correctly but I would not trust that too much given the dual exhaust mod.

 

Throttle position sensor, manifold absolute pressure sensor, o2 sensor, idle air bypass solinoid, timing, ignition module... take your pick the list goes on. Pull the codes with a code reader. Anything could be wrong or it all could be wrong!

Pull the codes that will narrow the guessing game.

Bob

 

I have seen a clogged cat and high exhaust temps burn exhaust valves.This might explain the backfire,the exhaust valve is not closing.I would do a compression check.

Billy