My guess would be 02's. but I think you said you replaced them. if your an auto, the 4:10's aren't helping if not diseregard... but what comes to mind is the 02's. I was getting crappy mileage and replaced 02's and it helped... so not sure on anything else that would cause it, unless the car needed a tuneup pretty bad..

 

yeah I thought it would have been o2's also but I just changed both of them along with plugs, wires, coil, opti, icm, fuel pump, and fuel filter. the car is a m6 . was getting same mpg before gear swap also. any other suggestions

 

My car is an M6 with similar bolt ons and 4.10,s and I get an average of about 20 mpg, with like 60/40 highway/city. My car was getting TERRIBLE gas mileage at one time, and it turned out my MAF was dirty from the oil on my K&N filter, I used some cotton swabs and some carb cleaner, not the best thing, but it got the job done, and now I'm back to where I was. I also have an exhaust leak out of my manifold on my pass side, I bet if that wasnt there I could get better. My car also runs kinda rich, even after a MADZ28 tune.

 

"false" leans are often the cause... misfires, exhaust leaks before the O2 sensors, faulty O2 sensors or O2 sensor wiring. What brand O2 sensors are you using?

 

Mine gets about 15-16 city. My best highway was 25.75 on a trip to Michigan this summer. Normal is around 24 highway. After reading everyone talking about the O2's, I'm going to change them when the new engine goes in this winter.
As far as I know they have never been changed. The car has 167,000 on it now.

 

So far, what I read tells me you have never used any scaning equipment except for codes. You likely have a poor tune in the car, too rich by far. Get a real tune in there, part throttle as well as wot, PERFORMED ON A DYNO WITH A WIDEBAND SENSOR INVOLVED.

 

He shouldnt need full dyno tuning with JUST bolt ons ...

 

the o2's i just had put in are ac-delco's and the scanmaster shows both banks working. at wot o2's read about 910-925. and i do have a pcm4less tune

 

Yeah it's a contaminated MAF. See them all the time from peeps using oiled cotton air filters. At this point even cleaning it probably won't change anything.

Oh yeah what's the fuel trims look like?

 

Speedy ~ Why wont it fix it? I understand it could take a little while for the PCM to readjust the BLM's and everything, but its not like the oil is going to permanantly ruin the MAF.

 

Does anyone have an actual dynotune and still get bad MPG? Mine just got a lot worse after doing full exhaust, but that's expected. Should be fixed after a real tune

 

So try cleaning it, what could it hurt? 2 things usually indicate the maf is bad. Big swings from idle to cruise. and the other is at idle it has negative fuel trims but at cruise it has positive fuel trims.

You can test it on the yellow wire by snapping the throttle and see if the repsonse is over 3.7V

 

I forgot to mention I also got a new ac delco maf and even cleaned it with electric component cleaner didn't change anything. blm's at idle are about 115-120, cruise around 120, wot 128.

 

I live in north Idaho.. Lots of mountains, but I don't drive have to drive in them much, so it's more or less flat for me..
But yeah, surprised the heck of out me...