Gentlement

I have a 96 1500 2wd w/4.3L/5spd. I just recently had a Flowmaster three inch single exhaust system installed. Now prior to this the engine light would come on once in a while, stay on for a few days and then turn back off. Well I took the truck to our mechanic to have him check the lights and install the system. Well he installed the system and called the light good. Well after I picked it up from him the light stayed on untill last night when I took it back and he said that the ECM says that the 02 sensor is bringing on the light. Well he told me that he sees this alot and sometimes it is the O2 and most times the new exhaust system caused it because of the different flow characteristics. Does this hold any water? It sounds right because the exhaust is flowing quicker past the O2 sensor. On the other hand I have never hear of this happen. What do you guys think?

Thanks

Nick

Nick,
The fact that the light was coming on before you installed the exhaust system tells me that it is not the cause of the problem. The free flowing exhaust might have made the problem show up more, but is not the cause.
Your "mechanic" should be able to determine why the ECM is setting a code, and the reason, by hooking up a good scanner and watching the inputs and comparing them to what they are supposed to be. It could be a bad O2 sensor, among other things. There are many things that can turn on the SES light, but you can usually narrow it down with the correct tools. I know plenty of guys with Flowmaster and other free flowing exhausts on newer vehicles that have no problems.
Hope this helps,

Bill

Yeah I figured it wasnt the exhaust, our mechanic is just always against anything aftermarket. He is a good mechanic, he just has his ideas how a vehicle should be left stock.

Nick

your truck should be OBD II, meaning more specific codes. older modles W/ OBD I codes were harder to track since a code could have several meanings.if it is a higher mileage vehicle i would start the diagnostic process w/ a new O2 sensor.

Jay

You do bring up a good point about the OBD-II. I know their tolerances are alot tighter than OBD-I. The truck does have 105k on it so he did replace the O2 sensor, hopefully that fixes the problem...

Nick