PNYXPRESS

A tune can't turn off all the o2 sensors. Only the rear two

The fronts tell the computer wether the engine is running rich or lean and adjust fuel accordingly. The rears only register whether the cats are operating properly or not. This is why they are able to be turned off, esp if the cats are removed.

Bigwedge67

A Tune?? I do not understand!!

Bigwedge67

Okay, Yesterday I bought a new EGR valve, throttle position sensor, New O2 sensors x3 MAF cleaner and throttle body cleaner. I'm going to put it in and clean the MAF and TB this coming weekend and post my results so that the next person that has this problem has something to go off of. I think I went a bit overboard, but for my son it's worth it. The car is in great condition and only has 90k on it. any other advice is more than welcomed!!!

Bigwedge67

As stated I'm getting like 10 to 11 MPG only, lets see what this does.

SteelerNation82

Well at this point, you're just throwing money away buying these parts. I replaced my EGR valve (for the hell of it) and it was caked w/ carbon but I later tested it on a bench w/ a vacuum pump it it held fine. TPS is very uncommon to go bad, they can be adjusted if they're off for some reason.

Did you pull the spark plugs to see what they look like? I know you said you had them changed recently but curious what they look like. And when this shop did the work did you have them scan the car for any codes (pending or stored)? Did the shop look anything else over with the car? I suggest you bring it back to them and have them take a GOOD LOOK at the car. What are the chances this car had thrown codes prior to purchase and the previous owner had the light cleared/reset? Another thing to consider.

SteelerNation82

And no disrespect to your sister, the previous owner. But referring to the engine light, sometimes it can be reset (unintentionally or not - reset code or unplugging battery) and it may not pop up for some time after a few drive cycles. Can take a few or hundreds of miles.

I forgot to ask also, did you have the battery tested/checked out? This is a biggie, due to all the sensors and electronics on these cars and can throw many things out of whack.

Bigwedge67

No disrespect taken. I did speak with my sister about the CIL she said she doesn't remember the CIL coming on. BUT!! As I sit here and type, the car did have that Amp Problem (The one where the Amp constantly stays on and kills the battery.) so they had to pull the fuse too it.) it kept killing the battery, so the battery was disconnected many times. it's not doing it now. (Something to think about though!!) I aknowlege that I am throwing money into at at this point and do not wish too. But it was on another Mustang site where a guy had similar to almost exact problems I'm having. "V6 w/5 Speed Manual was getting 12mpg before we did the following New Plugs, wires, Cleaned K&N air filter, MAF Throttle Body. Insatalled new PCV & EGR, Throttle position Sensor, and Fuel filter and new coil pack. Seafoamed the throttle bodyand added lucas fuel injsctor cleaner to the gas tank the the car is getting 19mpg."

So I figured EGR, Clean MAF, and Throttle position Sensor only cost me around $90 total so give it a shot. was 3/4 of the way there anyways.

Still open to everyone advice. Keep you fingers crossed for me.

Bigwedge67

Okay, I've changed the 02 Sensors, cleaned the Throttle body and the Mass Air Flow, still no improvement. I purchased a new EGR valve, I guess it will be my last hope. Been reading about the EGR valve and Throttle positioning valve some peeps say it has something to do with your mileage some peeps says is doesn't. But I figured sense the one on the car is rusted might as well change it out anyways. Doubt it will help but at this point it can't hurt. After this I'm clueless as to what to do. The only other thing I can think of would be faulty fuel injector. But wouldn't that throw a code?? As stated in my post the car rolls freely, bearings are good and calipers are not sticking. Still hoping someone can post what they did to fix this problem because from googling it; it seems to be a common problem with 1999 sixer's.

Bigwedge67

Resetting the computer is something I haven't tried yet, Let me give it a shot!!!

mustangman02232

What kind of roads were you driving on? If it's a lot of stop and go traffic that seems about right, just because it has the v6 doesn't mean it's good on fuel, my 99 GT was actually better on fuel then my v6