Does a faulty O2 sensor always produce a Check Engine Light?

gtrag94 · 08-30-2002

i have headers, OR h pipe and flowmasters. my question is would a faulty O2 sensor always produce a Check Engine Light? I have never replaced them (81k) and i think that I might as well change them and see if it solves my constant intermittent missing problem, either that or the timing is too high but it doesnt detonate so i dont know. another thing is when i put the MAC Equal Lenghts on there the EGR tube didnt reach so after fooling with it forever, i ended up cutting it in half and criming the one end shut on the header side and left the egr valve open. i can feel it pull a vaccuum at idle and it increases with rpms. Is this alright to leave this sucking in air like that or should i really fix this? would it cause WOT maladies? or some small idle problems? Thanks Criag

Amustang42 · 08-30-2002

It never hurts to put in some new O2 sensors with that many miles. I would definitely recommend getting your EGR fixed. Have you pulled your codes lately? When was the last tune-up? The EGR can cause some codes if it is not functioning properly.

gtrag94 · 09-02-2002

CEL is not on, fully encompassing tuneup done about 9 months ago and i havent been able to pull codes yet, i think timing might be too high because if you listen really really close to the area under the intake it sounds like a diesel and power drops off somewhat noticably after 3500 rpm or so. at WOT it doesnt sound like detonation... so i dont know?

GTRaptor · 09-03-2002

Could be detonation even if you dont hear it.
If intake or coolant temps are higher than normal the EEC could be pulling out some timing advance.

I say fix that EGR, a muffler shop can solder a tube extension.

C J · 09-03-2002

"i can feel it pull a vaccuum at idle and it increases with rpms" if thats the case then either the EGR valve is stuck slightly open or the EGR solenoid is bad. there should NOT be a vacuum in that tube at idle. also if that tube is open to the air then above 2000rpm or on acceleration there will be a big vacuum leak and will lean out your fuel mixture.
get the tube connected between the EGR and Exhaust header then find out why the EGR is on at idle. BTW: MAC says to flip the EGR tube to fit on their equal length headers, it worked on mine.

also, what is your timing at?