Well, I posted this as a reply to a thread about CAI and gas mileage, but figured I might get a better response as its own thread. Sorry about the double effort.

I installed the JLT CAI and the SCT 93 octane tune (via Xcal 2) this weekend - something very strange has happened to my mileage. I was getting in the neighborhood of 18 MPG.

When I installed the tune, I had 4 miles left to empty with 87 gasoline. I installed the JLT CAI and tune, then put about 3-5 gallons of 93 in (had someone pick it up from the gas station) before starting the car. I started it, and it said 0 miles to empty. I drove about 3 miles to the gas station and filled it with 93. Before, after a fill, I was getting 300 and change miles to empty. This time it said 194 miles to empty.

Once I started driving it, that 194 dropped very quickly, 193...192..191, etc., even though I hadn't even gone a mile. I was showing 11 MPG!

Well, it slowly but steadily climbed, but it's still hovering in the 14-15 MPG range (I've probably driven 100+ miles since the tune). This is a little disturbing. Has anyone else had a similar experience? Will it normalize again after just driving it and letting the computer get used to the tune or something? Should I make some kind of adjustment, like resetting the computer?

I also have to say, it could just be that I'm not that sensitive to it, but the CAI and tune really didn't seem to make that much of a difference. Some people described it as night and day, or like a bat out of he|| after the tune - my car felt roughly the same.

No CEL, btw.

Would appreciate any advice/help. I'll eventually take it to a DYNO so I can see if it's just me. I'd like to get an "official" idea of how much hp gain, if any.

 

Make sure the car is level and not moving when you reset the milage and try it again. I did have something strage happen with mine when I reset it once when I wasn't on level ground.
Hope this helps.

Steve

 

check to see if your jlt fell off!!!!!

 

or maybe your SLPs . . .

 

I believe what's happening is this..... If you reset and are idling and or just getting going very slowly , the mileage will show very low, because it has very little to go on. Same if you are cruising on the highway and reset, it will read as high as 32/34 mpg ....for a bit until you change speeds or road conditions. I would'nt worry about it.

 

I f your car does not seem any different after the tune then the tune did not take for some reason, reflash the computor again, if no difference something is wrong with the tuner. Once it takes you will see a big difference.

 

I have heard that when you install an aftermarket tune it can produce erronious reading in the info center. I recomend disconnecting your battery for 15 minutes to reset your computer. start her up and let it idle for 1 minute, then a/c on at idle for 1 minute then drive 10 miles so computer can relearn idle. this seems to make a difference in the way the car runs too. it clears out the stuff the computer learned on the stock tune and starts from scratch with the DTP tune. I had a similar problem but not as bad. stock mine always read 302 miles to empty when filled. after DTP tune it was 285. after reset its 324 now. calculating milage the old fashon way I was always getting around 320 miles per tank with DTP tune.

 

Thanks, guys. I'll try some of those suggestions. What's the best way to disconnect the battery?

Also, if I reflash the computer, should I flash it back to stock first then try to do the tune again?

Thanks! :worship:

 

N o you don't have to reflash back to stock just put it in again.

 

twice I have gotten gas where the computer and fuel gauge still showed near empty. I turned the car off, restarted and everything was working properly. When I first installed my SCT flash my I had to reset the console and drive go through 2 tanks of gas before it started showing the proper mpg.

 

So to summarize the advice I've gotten - I possibly need to reflash the computer with the 93 tune again, and possibly need to reset the computer, i.e., disconnect the battery and follow subsequent steps. Should I try one before the other, or just do both at the same time?

If I were going to do both, should I retune first then disconnect the battery and reset computer, or reset computer by disconnecting battery, then going through subsequent steps (idle 1 minute, drive 10 miles, etc.)?

Thanks again, everyone.

 

I suggest flashing the computer to the tune you will use, then reset computer with battery disconnect. then it will relearn with the new tune. Worked for me.

 

Cool. Thanks!

 

Well, not to add avgas to the fire...but....

my car normally says 253 until empty after fill up. I recently took a long highway only trip. After a fill up on the way it went to 273 until empty and my fill up at the end it was at 303 until empty. On my return and doing my usual backroad "Dukes of Hazard" driving it dropped down on every fill up till I am at 253 again. The "Milage till empty" takes into account all driving milage before last reset. I assumed once you reset it and are goosing it a little it gives you a shiffy result until the history builds back up.


Wrong or right....I don't care!

Jay

 

OK, I went to the shop today to have gears, and X-pipe and underdrive pulleys installed. Before doing that, I threw her on the DYNO. I'll try to post a picture of the sheet later, but for now - she made 278 peak hp. Considering that the owner of this shop (Mustang Magic - webpage) dyno'd his stock '05 GT at 277 by just removing the HC trap (mine was built after April and didn't come with it). Strange thing was that the A/F was right on, around 12.6. Could be a little leaner. At the shop, flashed it back to stock and then, a little later, re-installed the 93 tune. Driving back from the shop (~1 hr drive), I noticed a difference. For the first time ever, when I opened it up WOT in 2nd, 3rd or 4th gears, it really slammed and then pinned me into the seat. I know some of this is attributable to the gears, but the throttle response feels better too. I don't know if its real or I'm imagining it, but it feels as though the tune "took" this time.

After the gears were installed, they had to change the speedo for me - unfortunately, the Xcal 2 does not yet have a lot of its options functional - awaiting new software. To do this, they first downloaded my tune onto their computer, and with their software, changed the speedo, then put the tune back in the car from their computer. It took a lot longer than the Xcal 2. I think it may have been this that helped the tune "take."

Gas mileage still hovering around 15 mpg. :scratch: Think I may just need to drive it a while, and maybe lean up the A/F to get back to the 18 range.

 

this makes no sense, when you reset the computer it will remove all of your "custom tuned" settings. you would then need to reflash the computer with the tuner.

 

Although I admittedly know virtually nothing about this, my sense is that you're mistaken. When you tune the computer, you load a whole new program (think of it as an OS on a computer) into it. It's not just a matter of loading new particular settings into the existing "OS" - instead, you replace the existing "OS" with the new "OS," and the new "OS" has a number of different settings. The old "OS" gets saved on your tuner.

Like a computer, disconnecting the power won't erase the software on the computer. Similarly, because you've erased the stock program when you tune, there's no way the computer could default back to stock settings.

 

The stock tune is neatly tucked away in the little black box.

 

Ilikebond you are correct. To shed further light on the subject, the computer has the ability to learn your driving habits and creates a fuel and timing statgy to accomodate your driving habits. these are the "settings" that are erased along with any trouble codes when the battery is disconnected. (like the radeo presets and the time on the clock) I believe that it is better to remove everything it has "learned" with the stock tune or any previous tune and let it start fresh with the new tune. I could be wrong and it may not be necasary, but it sure wont hurt. :flag2:

 

I believe the radio set and clock have some sort of back-up.