Dyno tune/ Fuel mileage question

[2003_MM_FYRE49]

Has anyone that has had a dyno tune on their car noticed a significant drop in fuel mileage? I was getting between 19-21 MPG before the tune, and now I'm struggling to get 16 MPG. I still have the 3.55's, cooler plugs, 180 therm, and underdrive pullies.
P.S. my foot is not glued to the floor board after the tune...LOL, I am not driving the car any differently.
Thanks,

Tim :fire: 49

[TAF]

Tim...you need to double-check that the program you got was for 3.55 gears and NOT 4.10's. I know of another member who had this after the Dyno-Tune...he sent his chip to Dennis to be re-flashed for 3.55 gears and he's happier than ever with the mileage.

Send a PM to BlackTerror...for details

[2003_MM_FYRE49]

Originally posted by TAF
Tim...you need to double-check that the program you got was for 3.55 gears and NOT 4.10's.

Send a PM to BlackTerror...for details

Had the speedo checked with radar at 30 MPH and at 50 MPH, both readings were dead on. I also spoke with Mac, he thought that maybe because I hadn't had my torque converter installed yet that that may be the reason. I'm keeping my fingers crossed that this is my prob.

Tim :fire: 49

[bugsys03]

Just got back from a 1400 mile trip and averaged 21.0 highway. First long trip with her so dont have anything to compare it to except other members posts claiming 23-24 mpg. Still get 16-17 mpg in town same as always.

[duhtroll]

I have noticed a drop in MPG since the installation of the 4.10s and the subsequent dyno tune. I would call it a significant drop.

Prior to any mods I was getting 24.5 MPG on highway trips. Right now I hit 21 on the same type of trips. I do not know if it is the gears or the tuning. The speedo is accurate so I know I have the right program (at least it's on according to those trailers that show your speed as you go by).

It isn't tire pressure, though I have played around with different pressures. I have had tanks where they were back at 32 PSI like they were when I got the car.

I'm not too worried about MPG because that's not why I bought the car - coulda gotten a 50+ MPG roller skate for that. Just noticed it since I have been keeping pretty accurate mileage since the mods.

Prior to stage I/tuning:

Mix city/hwy - 22
Hwy only - 24-24.5

Post:

Mix city/hwy - 17.5-19 (sometimes due to repeated stomping, but not all)
Hwy only - 21

Any ideas from folks out there? Would be nice to kick this up a notch if it's possible. Planning on doing the exhaust next spring or summer and that might help some.

Thanks,
-A

[jgc61sr2002]

I'm sure the 4.10 were reduce your mileage. Although I don't have a 4.10 rear my mileage with the 3.55 sounds about the same as yours. (with the 3.55):(

[SergntMac]

4:10 and the supercharger, I'm holding steady at 20.5-21.0 MPG on the highway, and I cruise between 75-80 MPH. However, city driving fluxuates. Sometimes, I get 16 MPG, sometimes 19-20. Maybe the quality of gas has something to do with this?

[2003_MM_FYRE49]

I opted to keep my 3:55's and am happy I did so. I think the reason I was getting the poor milage after the dyno tune was because my computer had to re-learn my driving habits. During my trip to Colorado last month the worst fuel milage that I got was 22.5 driving through the Rockey Mountains. The best I got was 24 MPG driving through Nebraska. during the trip through Nebraska I had the Cruise set at 80 MPH the whole way. I'm sure if I had knocked it down to 75 I may have gotten about 25 MPG.

Tim :fire: 49

[LincMercLover]

I've got a chip and kept my 3.55's. Only thing is my gas gauge was busted during the tune, and a couple weeks after. So I duno about the whole re-learning thing... But I do know I was surprised at how slowly the needle drops now as compared to before. I haven't calculated it yet, but I can easily get over 300miles to a tank of gas with a lot of playing.

[John F. Russo]

SergntMac

Data
-I got 18 miles/gal. during the first 1000 miles of car mileage. ( I drove a steady 80 mph on the Penn State turnpike from Kenny Brown's place.)
-I've checked the mileage (18.5 miles/gal.) one other time when driving back and forth to work on a highway (75%) at about 70 mph and 25% of the time in local.

I check the gas level in the tank by painstakingly filling the tank until I see the level of gas in the neck of the tank each time.

So why are you getting from 2 to 3 miles/gal. more than me even though we have the same basic conversion from Kenny Brown? This is a significant amount of difference.

________________
2003 Blue 300B (Canadian) (reversed traction control, mini spare,
trunked 6 disc CD changer,clock-in-the-radio, heated front
seats, hood light)
-Born 12/10/02
-12,000 miles
-18 mpg at a steady speed of 80 mph
-Stock transmission (upgraded with Performance Automatic
clutches and band after stock tranny failed in 8,800 miles)
-Wheel locks (Ford)
-Badgeless front grille by “Zack”
-Zaino waxing
Kenny Brown: 6th “signature series” conversion (450 hp) Born
3/28/03
-Dead pedal
-Baer front brakes 14 in. two piston, vented rotors
-MMX Driveshaft
-377 RWTQ
-4.10 gears
-Vortech supercharger (7 to 8 psig boost)
-Pirelli P-Zero Asymmetric (front 255/45ZR18 99Y;rear
255/50ZR18 102Y)
-FordChip
-One coil of each front stock spring removed to produce
the “same” effect as an Eibach spring
-Ground clearance: 5 in.

[SergntMac]

Originally posted by John F. Russo
SergntMac...I got 18 miles/gal. during the first 1000 miles of car mileage. ( I drove a steady 80 mph on the Penn State turnpike from Kenny Brown's place.) I've checked the mileage (18.5 miles/gal.) one other time when driving back and forth to work on a highway (75%) at about 70 mph and 25% of the time in local. I check the gas level in the tank by painstakingly filling the tank until I see the level of gas in the neck of the tank each time. So, why are you getting from 2 to 3 miles/gal. more than me even though we have the same basic conversion from Kenny Brown? This is a significant amount of difference.

Yes, this is a significant difference in MPG here, John, and I cannot imagine why. Nonetheless, I am seeing 21-22 MPG driving OTR, and I can prove it...If that is what your are asking.

If not, it could be a myriad of minor settings, like tire pressure, air filter condition, (and location), gasoline octane, (both in Indy and in your home "twenty") weight inside the vehicle, and engine break-in.

Could be a lot of stuff, John, let's compare notes?