silver91gt

good answer

chinawhite

So are O2's needed or not? How much do they cost to replace?

And for a '95, full exhaust and 3.73's, what mods would help in the higher rpms?

vfast

what are the codes?

wildstang87

what octane fuel are you running, and what is your timing set at?? the thing with O2 sensors are, when they go bad the computer goes into limp mode, or a preset fuel curve based on load, and engine rpm. this will always make the vehicle run rich, not LEAN, as to keep any chance of detonation at a minimum. i say check the timing, set it back to 10°, and run some 89 octane fuel, see if that takes care of the spark knock.

vfast

pul the 02's and atleast clean them to see any change even after 30k or so they get a residue on them and are less precise with their signal back to the 'puter

wildstang87

its never a bad idea to clean or replace the O2s when they got mileage on them, but dont ever change them to cure a problem. if you truly understand how a converter, and the O2s work, take this in, imagine a obd1 car with an o/r intermidiate pipe, and what do you think the O2s are going to tell the computer??? then add in the fact that most 5.0s bypass the smog pump, and what do you have?? still a very streetable car that has no driveability problems. just dont ever believe the O2s will cause you more than gas mileage.

vfast

well that's not quite right...if your car is showing a lean condition on some 'puter will pull back time as it will trigger the spark knock in turn loss of power....the is so true on OB11's

wildstang87

you are very right, if your computer gets a lean condition it will lower the timing, but who is talking about a lean condition?? anytime the o2s go bad the computer goes into limp mode and you will be a little rich, not lean. the O2 sends a voltage signal to the computer. the signal is always between .1 and .9 volts, .1 being lean, and .9 being rich. the computer doesnt take action until either of those numbers are hit, if youre sitting at .8 the fuel and ignition curve are the same as if you were sitting at .2. once you hit .1 or .9 the computer will change the injector pulse to compensate and to get the a/f ratio back into parameters.

vfast

the guy stated it's running lean and has a spark knock...