For the last 3 weeks I have to drive the old mavdog to work ( well one day in and 3 days later home) 85 miles each way getting 19.4 - 19.6 - 19.8 mpg I'am thinking the milage could be better it I were not turning the engine so slow 1750 rpm's at 65 to 68 mph . 5.0 efi aod 3.00 rear gear 26'' tall tires your thoughts ??? Jay
Jay, that might be a problem if you are not running the O2 sensor and the car thinks it's going up-hill because of throttle position. However, a rustang with the same set up might be running at the same RPM. An easy way to check is drive it in high gear without OD and see what your RPM is and check your MPG. The other thing is tire presures. less then 30psi will eat up MPG.
LOL my car hits 3 grand at 60+mph. I have no idea what gears I have but sheesh. I'd like to see it hover at the 2K mark at 65mph. I drive my Comet 30+ miles every weekday and then maybe 20-40 more on the weekend.
Typically slower engine speeds yield higher mileage. Tire pressure, ignition curve, fuel ratio are places i'd look. Engine temp can also play a part, especially with EFI too cold and the computer is in warm-up mode and can use a lot of fuel. Too hot and you eat up power with friction. If you run the factory computer a properly working EVAP system can increase gas mileage. And any codes set puts the computer in FMEM(Failure management emergency mode) reducing the ignition timing and setting a very basic fuel map. I used to get ~24 MPG with a 3 spd 302 2bbl, 2.72:1 rear ratio and 26" tires.Of course, in general, a stick gets better mileage than an auto, but with EFI and OD you should be able to achieve that.
1750 at 65 mph is not enough RPM for the engine to operate efficiently IMO. A short stroke engine likes a little RPM.
If the engine is bogging down at that RPM and you using more than 40% throttle to hold speed, more RPM is the answer. And that may be true, depending on a number of factors(cam, heads, headers, etc). After all I got my best MPG at 60 MPH turning 2110 RPMs(high gear 1.00:1). I would definitely be interested in a test of the MPG difference with and without OD.
Thanks for all the input . Will have to check the HUGO relay to see if its working , add tire pressure, and so on. All systems are stock 88 fox rushtang the only thing left out is the air pump. Will update later. Jay
FWIW I've seen bosch 02's reduce milage a bit.Make sure your grounds for the o2 is good also.NGK/NTK or oem ford is usually best I run my tires at 40 psi also and drive with a feather foot
I just replaced the 02 sensors on my 95 mustang a month or so ago. It was not setting off any check engine lights, or causing any issues with driveability befor the swap. I was just putting in a new x-pipe and figured I would do it just because.......... Well my performance was instantly noticed, when I left the driveway! And I nalso noticed a large difference in my MPG (sorry no actual numbers, my odometer is broke LOL). I would change 02 sensors if you have more than 50,000 miles on them.
