Don', are you 100% sure that you are actually getting that low of gas mileage? If you fill up your tank to the top, drive 35 miles, and fill up again, it's taking 5 gallons to refill? Have you tried topping off your tank, taking a gas can, and just driving until it runs out and measuring your mileage?

You can't trust your gas gauge at all. The fact that it drops at a certain rate has nothing to do with your actual gas mileage. Your gauge can be affect by a lot of different variables.

If your mileage is really that low, the fuel has to go somewhere. If the exhaust fumes don't smell like pure raw gasoline, then the gas tank itself or a fuel rail should. It shouldn't be hard to find.

At this point a "regular" shop might be your best bet. So far you haven't had any luck with your performance shop other than having more parts pushed on you as a possible solution with no actual diagnosis. Suggesting it "could" be a fuel regulator and selling you a used one that they happen to have, with no idea whether that is the issue, no guarantee that it will fix the problem and no idea whether the regulator is need or whether it works, is poor business practice at best, and sounds slightly worse than crooked. A non-performance shop might be your best bet at finding a fuel leak or an engine issue. I'd find a reputable shop and tell them your problem, ask them to give the car a looking over and see what they find. Explain in advance that you don't authorize any repairs without your permission and that you just want them to find the problem and get an estimate to fix it. It's not like they're installing and degree-ing a cam, just looking over the basics. I think you have a good chance of getting this problem fixed really soon if you just bite the bullet and let the "regular" guys take a look at it.

But if you insist on a performance shop, did you try that place I suggested in New Braunfels? With the problems you're having I wouldn't give your shop the time of day. This is a problem that should have been found and fixed in a day, not months.

 

Ya man, I usually always fill my tank up, unless I'm in a hurry...

So by doing so, I calculate my mpg by filling up the tank, driving XXXmiles, filling the tank back up. And then divide the total miles driven by the number of gallons used to fill it back up. I know they're are no issues with math comprehension.

And I just hate going to a regular shop, bc I feel as though they don't understand the performance mods/tuning that is involved with the car...

What place did you recommend in New Braunfels? Henderson?

 

I always try to keep the RPMs low. But there is an issue with the tune, my RPMs hover at ~1500rpms when the AC is on for a few seconds, and then drop. Its MF annoying, but its been doing this for ~2yrs, just never got the tune fixed. I know that that is where some of my shitty mpg comes from, but this recent shitty mpg has to be something else.

Keep in mind, this is 100% city driving as well. I vary rarely drive this car on the highway.

 

Yep, that is how you figure mileage. Just wanted to check.

Most regular shops don't understand modifications or how they work, but this sounds like a pretty basic fuel leak. The gas has to go somewhere and I think you need someone else to try to find out where that fuel is going who can look at things completely unbiased without trying to push more parts on you that you don't need. If a regular shop says there is not leak, then maybe it is just a tune issue, but that's hard to believe. My Z28 dropped quite a bit of fuel mileage after my exhaust install when I went from 100% stock to off-road, but it was obvious. You can smell the gas and it'll make your eyes water if you're near the exhaust more than a few seconds. It's obvious to everyone around that it's running rich and needs a tune. If you don't have that problem, then it's got to be leaking somewhere.

I recommend at least talking to Henderson. I'm not affiliated with them and I've never had any work done by them, it's just that when I've gone in there they were always happy to answer questions without pushing their parts or services on me. And I've seen some of the cars they've worked on and they do good work.

 

Well I'm taking the car back into Lethal tomorrow at 10am. It rained ~5 days ago, and the car began bogging down bad (which it usually does, I think my MAF is somehow getting wet). Either way, it still bogging down. Right before I hit 2k RPMs it hesitates/sputters.

 

What are the symptoms of a bad MAF?

Also, I'm not throwing any codes...

 

Our computers are suppost to compensate for cold, but iv experianced with a rich tune very cold weather can bog the cars down. So it could have been just how cold its been lately and you running a rich tune.

 

Well all this started happening when we had that constant 100+deg weather.

 

It sounds like a problem with your tune for sure. Not sure if you lost tunning or what but my 2002 ss did the same thing after heads, cam, and intake install with bigger injectors. It would only get like 6 mpg. It was a problem with the tune. My car was an a4 with a 3600 stall.

 

I would say, get your fuel pressure checked out.

Also, get a locking gas cap, times are tough.

This has to be a fuel issue. What size injectors are you running?

 

i've read a hundred of you're thread on you're pump...gas watever problems...hope you get it fix. I think the t/a is cursed.

 

Not that my opinion matters any differently than anyone else's on here, but.... If Lethal or whoever is working on that thing can't get it straightened out, take it to a reputable regular shop for a thorough checkup (fuel pressure, regulator checks, leaks...ect.) If all of that checks out...then find someone who CAN tune to un-**** your tune....it's obviously not right. A bad tune can cause horrible gas mileage, O2's to go bad-which makes mileage and drivability even worse.

Installing a wide-band and looking at the AFR through HPTuners or EFILive would probably be the fastest way to eliminate a lot of the variables.....of course that's just me, it sounds like you don't know very much about cars... keep everyone posted, and good luck, hopefully whatever is wrong surfaces soon and it won't cost an arm and a leg to fix.

side note/afterthought: sounds like there have been a lot of changes in the car (a4 to M6 and so on) .... but just for argument's sake and to keep it interesting who want's to bet it's the tune?

 

Hell with gas milage like that you would actually save money by spending the 200 or so to get a professional tune.