ridiculous gas mileage

[dutch]

I think it started when I had the 3.55's put in, but I'm not sure. Anyway, I've been getting ridiculous mileage lately.
Car is basicly stock and had a good tune up in march (haven't driven it much this summer).

- new O2's
- new plugs
- new plugwires
- new cap+rotor
- new fuelfilter
- cleaned MAF

It's always been getting reasonable mileage for a mustang, but lately I've been struggling to get 100 miles out of half a tank.
Last sundaymorning I drove 90 miles behind some old mustangs doing 60-70mph on the cruisecontrol on an empty highway and still the same..
Filled it up 2 days ago, drove to work twice (mixed traffic) and it's already at 3/4 of a tank after just 30 miles of well behaved driving!!! (that's 30 miles on a 1/4 of a tank including whatever there was in the fillerneck)

cars runs fine and pulls good. No excessive backfiring or black smoke.

pulled the codes for the first time last night to see if any sensors were acting up..

First with the engine off/key on

- self test: 111 (which means there are no codes right?)

- right after that another 111 (which means no stored codes right?)

- with the engine running, it started revving to 1500-2000 for a while and then returned another 111, after which I turned it off..

So no codes?

I'm stumped. :dontknow:

 

[CC'S95GT]

111 Just means the ecm is working. you'll get everytime. did you do the cylinder balance test?
pull a couple of plugs and see how they look.
how old are the cats? they might be plugged and due for changing

 

[dutch]

didn't do the cilinder balance test.. no cats, o/r H

 

[Steven]

Mines not far from that. I get crap for mileage.

 

[red95r]

mines horrible, and i have a v6. with the ac on I barely get 80-85- miles to half a tank. I've done everything you have cept new 02 sensors, and a coil pack.

 

[dutch]

Are there any places in the fuelroutes thats prone to leak with these cars?

 

[Win]

Do you smell fuel ???? Like Raw gas?? If you smell it more then when you put on your O/R pipe then yeah i would begin checking. There is a sticky about the possible fuel leak

 

[dutch]

I honostly don't know, sometimes I think I do.. but then again, it has always done that since the o/r pipe.

 

[Win]

I honostly don't know, sometimes I think I do.. but then again, it has always done that since the o/r pipe.

It would be a absurd smell usually but don't rule it out just yet.

I get about 13.5mpg in my car. I have a 7 mile trip to work that's it. I get bad MPG because of that. Now once i get on the highway and cruise that's a different story. I pulled 26mpg on the move up here with 3 dogs, me blasting AC the whole way and a fully loaded car.

Have you checked your Balancer. I think you had problems with it before right. Also do you have your EGR tube hooked up to your H pipe??

 

[Inspector13]

I average around 20/21 mpg in my Mustang and it absurdly smells like gas with my O/R prochamber (it burns my eyes after about a minute of running in the garage).


Hope you figure it out.

 

[dutch]

EGR is connected and balancer is replaced and hopefully ok.. I've been reading up on the filler neck problems, I'll check that out tomorrow.

 

[Paul]

I only got 18-19 mpg in my car when I daily drove it. Your mileage isn't ridiculous, just not great.

 

[cntchds]

I get around 17, depending on how much I beat up the gas pedal. For whatever reason, I get around 80 on the first half of the tank, and another 140 or so on the second half. I've given up trying to understand why our gas gauges act the way that they do, but I have also realized that even if I'm below the E when I fill up I only get about 13 gallons into it.

Before I did the head swap I was getting between 12 and 14, now with the GT40's I'm up to 17. With that logic, the bigger the better, get some AFR 220's and you'll be getting great mileage.

Or you might have a blown head gasket, and you're burning epic amounts of oil like I was, and would be getting better mileage if you just changed the head gasket... Either way.

 

[P51CrazyHorse]

My '98 3.8L with over 200k miles gets average of 26 mpg combined city/highway. Even when I use the A/C. I usually drive until the tripometer reads 360 miles before I fill up again, and still have a little bit left in my tank at that point.

Only mod I've done to my car (aside from replacing worn out stock components such as brakes and tie-rods) is a K&N filter.

When I was only driving city, no highway at all, I got around 20mpg. If I drive nothing but highway constantly, I get right at 30mpg. As it sits now, I drive mostly highway to and from work, with a little city driving at each end of the trip.

 

[username182]

Sounds like what I get.

I get 200 miles on a tank, I fill up 13 gallons, so 15mpg. That's city only driving, 15 mile round trip to work Mon-Fri.

When I had my built auto and 3000 stall converter I was getting 150-160 miles to a tank lol.

 

[CC'S95GT]

I'm getting about 18 mpg, mostly hwy, @ 80mph. with 4:10's. What kinda plugs did you put in? 5.0's don't usually like platinum's. I am also using a MSD cap and rotor if that makes a difference. My last tank I got 240 miles to the tank (fumes)

 

[96_SVT_Cobra]

ive been in the single digits for mpg's once or twice. most of the time its about 12 mpg. good thing its not my DD. also i hve no idea what to suggest for you, did you use ford parts or aftermarket? was the milage this bad before you did the tune up?

 

[dutch]

Mileage was fine before I did the tune up, I do it with every car I buy for piece of mind.

motorcraft plugs, FRPP leads, MSD cap+rotor, motorcraft O2's, nothing but the best.

 

[mustangshane]

I get 230 miles per tank city driving and about 350 miles with the top down on the expressway. Just for comparison.

 

[dutch]

got about 200 miles combined from this tank....