O2 sensor bad= poor gas mileage
 

What I have is a 86.5 Supra with a rebuilt 7mgte, 57 trim, driftmotion ic set-up, 3inch exhuast all the way back (too loud for my taste) and a intake. Haven't changed the fuel pump yet, it's still the N/A pump but have a walbro fuel pump to drop in.

So, I've searched and came with nothing. I have replaced my O2 sensor a few times, it works great up until I hit boost (stock) and my cel comes on. once that does I get really shitty gas mileage, Im talking 220 miles to the tank at the most. When my O2 sensor didn't go out the needle on my gas gauge would just stick forever and not budge. Can anyone chime in on what could possibly be the problem? All help is definitely appreciated since I'm moving down to Arizona for school and don't want anymore poor mpg

What you describe isn't consistent with a bad O2 sensor.... It's more consistent with a bad AFM, excessive engine knock, bad knock sensors or wiring, etc.

Have you bother pulling the diagnostic codes? If you don't know how look in the MKIII FAQ section for a thread on how to do it.

Yes I have, I have a code 34 and 41. I just remembered I pulled the cps out and didnt jump the terminals for timing. Ill jump it, start it and see if there is any codes after that and let you know.

34 is most likely the issue and timing isn't going to cause it.

Okay, I'm using the stock 7mgte afm but with the Lexus electronic. Is testing the resistance on the Lexus the same as the stock 7mgte meter? Of course Im testing it now to make sure its in spec, if it is the same as the 7mgte's.

Im also running an upgraded ct-26 with a 57 trim.

Yes, the actual sensor is the same... Same part number even. The method of testing in the TSRM isn't 100%... You'd need an oscilloscope and Toyota's advanced diagnostic publication to really test it. Has the air bypass screw been tampered with?

I couldn't tell you... the screw is 3/4 of the way in looking into the chamber. Not sure if that helps or not.

If you can see the screw, then the pressed in cover had to be drilled out and it's most like been screwed with (hehe.... pun)... See my thread in the FAQ on how to reset it to it's factory position. This isn't going to be the source of your error codes but may further contribute to fueling issues (especially if it's in further than spec).

I'm sorry, I was referring to looking inside the chamber of the afm. the pressed in cover is still their, hasn't been tampered with.

Also I fixed the problem, didn't even think to check the wiring at the connector, it was bear with lots of PS fluid on it, cleaned it and now no more code 34 or 42. Drove around my neighborhood with the diagnostic jumpered and have a code 51. Must be because of no A/C.

Cre, Thank You! Without you I would be a lost cause not knowing what to look for. I know UTI will help me with that =)

Fix the code 51 if it's genuine. You cannot set the ignition timing with any error codes present. The code 51 won't stay stored. If you press the throttle while in diagnostic mode you'll get a code 51 but if you take your foot back off the throttle and the A/C signal is correct (off) then the code will go away again after 30 seconds or a minute.

No sweat.