Bad Mileage

trickyshadow · Sep 1, 2005

I need alittle help here guys, I have an 01 GT installed 4.10"s and a Diablo chip, my city driving has gone from 16-17 to 21 miles per gallon mainly because I am using 5th gear more around town but my highway mileage has gone from 26 down to 15 miles per gallon. That's at crusing around 70 and not putting my foot into it. Is this normal or should I be looking for a problem some where, thanks for any help I can get on this problem.

Seraphitia102 · Sep 1, 2005

It's normal for 4.10 gears. 4.10 gears depreciate your mileage badly on highways. 4.10's are worse because they cause your engine RPM's to stay at about 3k or 3.5 as opposed to 2k rpms (on stock 3.27 gears) to cruise on the highway.

Engine at higher RPMs on highway steadily = loss in mileage.

trickyshadow · Sep 1, 2005

I knew I would lose some mileage but not 10 miles to the gallon. Is there any other mods I can do to get some of it back? I am just glad I dont do much highway driving.

Kilgore Trout · Sep 1, 2005

The 4.10s make your engine rev higher to achieve the same speed which decreases milage. I have never heard of it being this bad though. Are you accurately measuring milage?

Kilgore Trout · Sep 1, 2005

To correct it retard your timing and switch back to 87

Mustangl3 · Sep 1, 2005

I have an auto and might have lost 1 or 2 miles a gallon cruising at 70 mph with the 4.10s so something might be wrong

forpit2000gt · Sep 1, 2005

trickyshadow said:
I need alittle help here guys, I have an 01 GT installed 4.10"s and a Diablo chip, my city driving has gone from 16-17 to 21 miles per gallon mainly because I am using 5th gear more around town but my highway mileage has gone from 26 down to 15 miles per gallon. That's at crusing around 70 and not putting my foot into it. Is this normal or should I be looking for a problem some where, thanks for any help I can get on this problem.

something else is going on, 4.10s do not cause you to loose mileage, your foot will because you stay in it more
anything else besides the chip be added or change. the chip may have something to do with it.

hotrodnut · Sep 1, 2005

Let me get this straight, you go to 4.10's and your city MPG goes up by 4-5, you highway MPG goes down by 10 and to top it off you highway MPG is worse than your city MPG. I can say something is amiss here, that just does not make the numbers add up. I can see a little gain in town since there is not as much load to get the car going and I can see a little drop in the highway because of the few more RPM's but to go up 5 for city and down 10 on the highway the math just don't calculate for me.

Kilgore Trout · Sep 1, 2005

Gosh, could 4.10s affect manual and auto differently? Survey says: YES!

forpit2000gt · Sep 1, 2005

he's a 5 speed.

trickyshadow · Sep 1, 2005

Yea I know it makes no sence but I have check it on 3 full tanks and the numbers keep coming up the same. City i can understand because I am using 5th gear more. I am thinking about pulling the chip and speed calibration on it just to see if it makes any difference. There are some guys in our local club running 4.10's and their mileage is no were near as bad as mine.

Kilgore Trout · Sep 1, 2005

Dirty fuel filter, dirty plugs and other preventitive maintenance items can cause poor milage...

forpit2000gt · Sep 1, 2005

trickyshadow said:
Yea I know it makes no sence but I have check it on 3 full tanks and the numbers keep coming up the same. City i can understand because I am using 5th gear more. I am thinking about pulling the chip and speed calibration on it just to see if it makes any difference. There are some guys in our local club running 4.10's and their mileage is no were near as bad as mine.

if the chip is doing the speed calibration, are you sure it is set for the 4.10s? your mileage will read differently if not and you may be figuring it wrong.

BooWFO · Sep 1, 2005

You have a 3650 right? cause I knock down 23+ mpg on the hwy. I avg 20mpg with comb. driving plus a night at the track spraying a 100hp wet shot.
Maybe try a different cruise speed? I know my Ram got it's best at about 68mph 65 she sucked it down 70 the same 68... well she still needed to have in flight refueling but it was 20% better. Which on it was just over 2 mpg.

Seraphitia102 · Sep 1, 2005

forpit2000gt said:
something else is going on, 4.10s do not cause you to loose mileage, your foot will because you stay in it more
anything else besides the chip be added or change. the chip may have something to do with it.

i thought 4.10's cause you to lose quite a bit of mileage? it says so on pg. 57 of the October 2005 issue of 5.0.

squares98 · Sep 1, 2005

I lost like 1mpg with my 3.73's.

Red03Mustang · Sep 1, 2005

I think something is up with those numbers.

Kilgore Trout said:
Gosh, could 4.10s affect manual and auto differently? Survey says: YES!

I have an auto, but I get almost exactly the same numbers city and highway as BooWFO does.

I think something is probably wrong somewhere. I haven't come close to losing 10 mpg going from 3.27 to 4.10. I lost maybe 1 MPG.

goshia · Sep 1, 2005

Try removing the Diablo Predator for a few tanks. The program that the Predator comes with makes your car run a little rich. I was getting 23-25 mpg driving between 35mph to 60mph. The when I installed the Diablo Predator the mileage on the same trips went down to 19-21 mpg. I have logged every tank of gas thas as ever been put in my car, starting at 13 miles on the odmeter

forpit2000gt · Sep 1, 2005

Seraphitia102 said:
i thought 4.10's cause you to lose quite a bit of mileage? it says so on pg. 57 of the October 2005 issue of 5.0.

I know it made very little if any difference on mine and many others I know.

That same magazine also showed bigger hp gains in bolt on parts that when done independantly tested, show much less or no hp gains.

Bullitt0616 · Sep 3, 2005

doesnt a diablo allow you to tweak your air/fuel ratio?

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