gas mileage worse after tune

[69cutlassrkt]

Before my car was tuned I was consistently getting 24mpg.
Now it its getting 15mpg mostly, sometimes a little less.

It seems like a huge drop in gas mileage to me and seems to be especially low for a 5.3 What do yall think?

[67zo6Camaro]

Tell us a little more about the motor, extras intalled, prior tune, current tune. Example....current tune is for a efi motor, agressive fuel curves...

Basically some more detail info about what you have...

Brett

[69cutlassrkt]

It has the later ls1 injectors an ls1 intake, Dougs headers, 3" exhaust. It has 2.78 gears in the rear end. This was all the same before and after the tune.
It doesn't have any dtc's except ones that have always been there. I'm not sure how the fuel curves are now. I know it was running rich before.

[MattG]

Something is not right. Almost without exception, after a good tune your mileage should Increase. I have seen it time and time again.

Talk to your tuner and ask if there was anything unusual to begin with.

I guess the only question is was there and obvious increase in power after the tune, if there was, it is quite possible that you are having more fun driving than you were in the past.

You tuner is your best resource at this point.

Matt

[MrForce]

Typically, that is overfueled and undertimed at cruise values. Short term fuel trims (STFT) should be going nuts on the scanner. Or MAP/MAF accidentally disconnected?

[67zo6Camaro]

Typically, that is overfueled and undertimed at cruise values. Short term fuel trims (STFT) should be going nuts on the scanner. Or MAP/MAF accidentally disconnected?

This raises a good question. When you say tune do you mean someone played with your computer map curves or do you mean that someone just put new plugs in, changed fuel filter, air filter ect..

The main reason I ask is that if you have the wrong injectors....24lbs vs. 28lbs, then if someone changed your fuel curves back to a standard and/or rich setting, then you could be getting exactly whats stated above. "overfueled at cruise values"

what was changed during your "tune" process?

[69cutlassrkt]

It was dyno tuned by snl performance in Haslet Texas. Even if I baby it and try to get decent gas mileage out of it all I get is maybe 16mpg. I did have my dad take it to the dyno shop cause the gas mileage was so much worse than before. I would have taken it myself but I had to work. And yeah Matt there was an increase in performance went from 252rwhp to 275rwhp. Torque increased on avg and the peak was about the same.

Thanks for all the responses. I too thought that after the tune it should get better mileage and not 9mpg worse. I guess I just wanted some reassurance.

[69cutlassrkt]

idk if this helps but this is a pic of the dyno graph and a/f.

https://static1.pt-content.com/images/pt/2010/09/kkessler1dynosheet-1.jpg

[Mach Par]

SNL is a pretty good shop. I would call them and see what they say. They are very stand up people.

[69cutlassrkt]

thanks. I think they are pretty good too. I'll probably just wait till I do something else to it to take it to them. Also I live too far from them right now until I move back to Fort Worth.

[overZealous1]

ask to have it tuned to 15-15.2/1 at cruise. low load 1500-2500rpm. can really make a difference in over all gas mileage. a good aftermarket a/f gauge will help you know where you are at.