Engine Running Rich And Backfiring.

PattyJoe

New Member
May 24, 2014
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I have a 95 mustang gt that is pretty much stock. I just got the vehicle about a month ago. The stock mid-pipe rotted out right at the cats so I took this opportunity to upgrade. I switched from the stock catted h-pipe to a Pypes off-road X-pipe. It sounds amazing. I am not sure if the problem I am having is related to this but it started occurring shortly after the pipe swap. My car hesitates under light acceleration and idles very rough as if it is flooded. It backfires excessively at low rpms until I stomp on it. Under hard acceleration the car runs fine. I can smell in the exhaust that the car is running very rich. I just did plugs, wires, cap, rotor, pcv valve, air filter trying to get it to run better but the problem persists. The idiot who did my exhaust used a torch to get the old pipes off the manifold and he did not put the O2 sensors back in the pipes. They are just ziptied up in my engine compartment and there are plugs in my pipes. I believe this to be the culprit of my problems but would that really make a difference seeing how I eliminated my cats anyway? Any thoughts would be greatly appreciated. Thanks!
 
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Well, you've described the problem, you just didn't realize it. The Mustang computer uses the O2 sensors to adjust how the engine is running. On the 94-95 5.0, the O2 sensors are put in before the cats; the computer doesn't care if you have cats or not. When you mash the pedal to the floor, that's called WOT - Wide Open Throttle. The computer does NOT use the O2 sensors under WOT, so the car will run fine without O2 sensors under WOT. Under partial throttle and idle, the computer needs those O2 sensors.

The easiest fix is to remove those plugs in your pipes and put the O2 sensors back in. Be aware that the mechanic that did your work might have damaged your O2 sensors. It's also possible that they're old and may not work well anyway. Your car will work better with the O2 sensors you have - but if it's still not running right, you might have to replace them.