Saleen1989

I'm in the need of some help.

I have a 1994 Mustang Gt (303) and recently installed a MagnaflowH pipe with catalytic converters (part # 93339) that is supposed to be street legal. It was installed upstream of existingFlowmaster mufflers.

The problem is that the check engine light (converter malfunction) comes on after is warms up and then goes off after the engine is shut off only to come back on after it heats back up again. It also has a slight backfire when cold. The car runs strong with no issues.

The O2 sensors (no CEL)were working fine up until the new Magnaflow system was put on.

I've disconnected the battery to reset things but that hasn't helped.

My mechanic claims that the higher exhaust flow is causing the problems and that new O2 sensors may not fix the problem.. Magnaflow , of course, thinks that the 02 sensors are not working properly (damaged during the install ?).

Am I causing any damage to the engine or converter operating it the way it is ?

If anyone has any ideas , I sure would appreciate it.

Thanks from NJ

WhiteWindsor

With most cars 90 percent of the time the cel will be the o2 sensors. But like your saying it could be either or. There is probably a way to check the sensors though i dont know how. I had exhaust on a chevy truck once that kept throwing the same code, i was told with my exhaust it could not be helped. But i think on most after market parts for our cars it should not throw that code unless something is wrong. I dont have the sensors but my car is a little different than most.

302f150

lol, the mechanic is full of it. either he broke them, or they arent working. they dont quit working when you flow more exhaust.....the computer only monitors the o2 sensors in closed loop(afer the motor warms up) so if one is broke, it might show an open, also, you installed the cats upstream of the flows, with the o2 sensors in front of the cats right? won't work right if they are downstream of the cats because the cats will even out the mixture and they voltage will not fluctuate like its supposed to so the computer will think they are broke

945LSTANG

i definetely agree with magnaflow.

i never threw any codes after my o/r h install.