Please Help! Major mpg issue after tune!

[GMC Z71]

I have a 2004 GMC z71 5.3. I had a guy put a tune to it and now I cant seem to get better than 11 mpg and thats on a good day. I have changed everthing that would consist of a tune up including cleaning my injecters. I brought my truck to him to tune for fuel econmy but lost major mpg sense then. I know he used efIlive so thought maybe someone may know something he dont? Please help !

[Taz]

There are many potential issues / causes ... you will need to post your tune for any type of specific answer.


Regards,
Taz

[N0DIH]

Stock truck or have 37" tires and 6.50's in there? 11's is only good when it is an ET! Got a cold thermostat in there?

For sure need to see the tune.

Any codes?

[GMC Z71]

I really dont know what tune exactly. I just know that my truck idles really low now and stumbles alot. My truck is stock. I guess theres no hope for me. I am going to have to ram clear my computer so that I can start fresh with a stock tune. The guy says he put my stock tune back in but theres no way running like it is.

[GMC Z71]

And no no codes at all.

[N0DIH]

Need to see what tune is in it and some datalogging to see what is going on. Diagnosing without a datalog is nearly impossible.

Have the guy hook up the datalogger and drive it and log. He should be able to tell you something just from that alone. With it that bad and no codes almost sounds like it is staying in open loop and something going on that isn't allowed to trip a code yet.

Is coolant temp getting up to 190+ F? Was it ever overheated?

You lost mpg before the tune correct? Tune didn't help, wouldn't expect it to, tunes aren't good band-aids for a bad part or an issue.

Find out if there is any recalls or service bulletins on it, GM did have some bad cams, but not sure what years.

[GMC Z71]

Nodih, You do have a good point. Yes it seems to be getting to 190. but not to 210. Also i checked for a recall but nothing for my truck. Well he pluged up to it and checked a few thing but says that all is good with what would affect mpg. Noih i am going to the GMC shop tomorrow morning and having my computer ram cleared so that i can get it back to stock. I brought it back to the guy who tuned it to put it back stock and he says it is but i can still go over 100mph and it is running like a spotted ass ape!! It has way more power than stock! also my shifting points are off sync. meaning it bangs out out before it shifts. When i do get it back bone stock if the fuel mpg is still sucky what would i need to do at that point??

[Gregs]

before you go running for the dealer i would clean the maf with some maf cleaner, a dirty maf can really screw things up with these vehicles without setting a check engine light