Crappy gas mileage...

[Cogs]

I'm currently getting 13.5mpg city, no matter how I drive. Last tank of gas was all nice driving this one is a lot of donuts and fishtailing and speeding. I drove 400+mi on the highway the other day and got 14.5mpg. That is NOT right. I used to get much better. I know my exhaust is one problem, I have a major leak between the header and H pipe, but what else could be causing this?

[phayzer5]

if you have a serious exhaust leak that close to the headers you're gonna loose a good bit of torque and that oculd cause you to use more throttle that you' should need to do things.. You might not niotice the dofference since you're used to its power

[Cogs]

There is a difference, though I think it may have been leaking a little when I got the car. I'm sure that is most of my loss.

[yucatec]

Didn't you used to get 21 highway? I don't know anything about a performance engine like yours but a 6.5 mpg loss without any awful performance symptoms seems most likely to be a gas line or tank leak. Donald McCaig

[grandpaslincoln]

There are a few things that can cause excessive fuel usage. For example:

A dirty air filter.
Incorrect ignition timing.
Incorrect Idle speed.
Low tire air pressure.
Binding brakes.
A fuel leak.
Malfunctioning Transmission.
Thermostat stuck open/not installed.
Dirty or clogged fuel injectors.
Malfunctioning Carburetor.

Check these things.

[NitroNic]

I've been getting 10.5 to 11.5ish in town as long as I Can remember... I've been driving this car for almost 4 years, the worst problems I've encountered since driving it are crap starters, bad air pump, water pump, misc brake part issues (mostly master cylinders and pbb's), and driver side windsheild wiper arm.

Maybe I should pull some codes, just for kicks? :dunno:

[Cogs]

Performance engine? :haha: Lol, if you call 165-ish hp performance. Anyway, I never really figured out my mileage before, just started doing it now. I estimated it at 16mpg city before though, which seems low. I got 18-19/21-22 in my 89 Vic. I'll probably just be driving the Nissan Stanza beater when I can. :cuss:

[85crownHPP]

replace your O2 sensor and check for vacuum leaks.

wait thats right you have headders... have you made sure you have o2 sensors anymore??
That would suck if whoever did the pipes left em out.

[Cogs]

Yep, I got em. And they're new I believe.

[88grandmarq]

usual stuff here..... first verify the 02 sensor harnesses have not burned against the exhaust. then check for vacuum leaks and pull the codes.
inspect the rubber hose coming off the back of the upper intake going to the MAP sensor, make sure its not cracked, broken or kinked.

and read the list G/L posted... espcially the one about the T/stat.

[Cogs]

I just looked at the o2 wires 2 weeks ago or so, they were fine then, Guess I should check again though. Ill check most of it out tomorrow. I know I have a new 160* T-stat which doesnt help gas mileage either...but I didnt put it in.

[88grandmarq]

toss that 160 stat in the trash. with the cold climate you live in you should run only a 195. install a fresh, 195 T/stat and check for codes.

let me know what codes you find, if any.

[grandpaslincoln]

I agree. Whoever installed that shoulda known better. Having a 160* is about as bad as not having one at all.

[Grand Marquis GT]

160 Thermostat? Whoever installed that was a fool.

Wow. Even in FL I run a 180...

[Cogs]

Yep, thats what I thought too, when I got the car. He said "I just installed a 160* t-stat, cause I didnt like how hot the car was getting..." I'm assuming it want THAT hot considering it NEVER has gone over 160 while I've owned it. At those temps the fuel probably isnt even being completely burned. Which means less gas mileage and probably less performance. :coocoo: