02 Gt Mpg Question S

[Master baiter]

I got a 02 vert gt. It has k&n drop in filter, pipes o/r x pipe, mil connectors, and flowmaster mufflers. Has 133,000 on the clock and is automatic. All I can seem to get is 17 to 18 mpg. I'm wanting to swap in 4.10s but my mpg is horrible now. Any ideas?

 

[IIGood]

What kind of driving do you do? City? Highway? How are the tire pressures? Have plugs been changed? What size wheels are on it?

It is a convertible too so it is slightly heavier than a coupe but I doubt that would make a difference.

My '03 GT coupe that is now back to stock except for the Bassani cat-back has always got 20 mpg in mixed driving, and 35 psi in the stock 17" tires. Had the plugs changed around 140k...its got 166k on it now. At one point I did have a K&N in it but switching that out didn't have any impact on fuel economy.

The best I ever got out of it was 30 mpg on highway driving, running around 70 mph the whole trip.

 

[Master baiter]

Hwy mostly, about 80 miles round trip a day at around 75mph. Factory size tires on factory 17s. I run 38psi. Far as tune up idk if it has ever had one or not.

 

[IIGood]

One other thing I missed from your original post is the automatic transmission. That will have an impact as well. Mine is a manual so that helps with the longer distances as far as mpg goes.

I had a V6 automatic before I had the GT and it got the same mileage as my GT does now.

So, transmission type also makes a pretty big difference.

 

[Master baiter]

Yea just seems bad. My 05 auto got 28 and my 07 manual got 32. My old 03 gt manual averaged 27 so I figured this one should do better then 18. Kinda afraid to drop in the 4.10s lol

 

[IIGood]

Something does seem amiss for sure if you're only pulling 18 on the highway. I honestly couldn't say what but since your pressures are all in spec and all that other stuff checks out, maybe something else is going on somewhere. Maybe try new plugs first and see if that helps.

Does it idle rough at all?

 

[Master baiter]

No idles great and runs great. Every once in a while she will stumble when u first start her but after 5 seconds it clears up. I'm wondering if it's sumthin in the trans. If I nail it at 60 it feels like it slips then slams into gear. Gonna try dropping in some e3 plugs, new coil boots, fuel filter, and change trans, filter and rear diff with royal purple. If it doesn't change then Nxt step will be a programmer.

 

[Master baiter]

Now this is my first vert so I'm not sure but are they governed? She don't pull much past 120 and never has got to 130. My 03 pulled past 150 with same mods.

 

[Master baiter]

Also I forgot on my 98 v6 5 spd averaged 26. I swapped the 7.5 with 2.73s out for a 92 Lincoln mark vii 8.8 with 3.27 track loc. Mpg increased! I could get 450 to 460 a tank.

 

[Master baiter]

I've got 115 miles and I'm a 1/8 under a half.

 

[GOKBGO]

You mentioned changing coil boots. Could be you have one or more bad coils. I've had to change all mine out at about 93K. Also, clean the MAF, throttle body, IAC valve, and use Seafoam in the upper intake and gas. Change the air filter if needed. Use the recommended 5W-20 oil. Use fuel injection cleaner in the gas. Hope you torqued the plugs to spec, else they will blow out. Make sure you use a 75W-140 lube in the rear, not 90. Source...an '02 GT owner for the past 12.5 years with 170K miles.