odd situation, runing lean

[Bad92GT]

So I bought my 95 7 months ago. It was the essential basket case, however I've fixed most of the worst parts. The only thing left is to solve the very very bad MPG. The car runs very strong, actually stronger then it should almost. I pulled codes, got EGR (there is no valve, just a block off plate), and a TPS sensor to high voltage, set screw to low for throttle, and ISC not responding correctly. The car even when running bad would just burn the tires off of it and run great up top, however idle problems and bad MPG plague it seriously. I've replaced all of these

New reman distributor
Ford racing wires
New cap and rotor
new NGK plugs
New motorcraft IAC
New cold air kit (the stock stuff was toast and leaking badly)
Alot of new vacuum lines
New ECT sensor
Long tube headers etc.

Theres a couple other things. I havent replaced the fuel filter yet, the car hasn't seemed like it needed one, never had a lack of fuel. However it only gets around 10mpg, and it doesn't matter how I drive it. I put a new IAC on it today as I work at a ford dealership and got it for cost, and most of my idle problems went away, however I don't think everythings gone. It will sit there and pur at idle, albeit a little high at first so i adjusted the set screw and IAC percentage via the allen head screw on the TB, and got it to idle like I wanted. The CEL is not on, but it will idle perfectly fine, no surging after the IAC install, yet it will suddenly make what sounds like 2 puffs of a bad exhaust leak and stumble slightly but catch itself and be fine. It's very odd, and I do know that the pieced passenger side header has a leak at one of the connections, So I plan to weld it up. Today I also installed the NGK plugs, and I pulled out the old set of autolite 24's someone previously put in it, and they were white as a ghost. The car is running ultra lean, but doesn't burn a drop of oil. The Plug has no smell of gas or oil, there is frankly no smell at all. I'm not sure what it is, it runs great up top but this mileage thing is killing me. I don't know what it is thats causing it. Brakes are not dragging, I installed new Ford OEM front hubs even and had the rotors turned. The rear is free, albeit a little wore out. Any suggestions would be appreciated, I'd like to get this maintenance out of the way so I can go on to installing my 3.73, axles, girdle, and trickflow heads

 

[Adam95GT]

O2's next id say

 

[It's a 5_0 HO]

Even if you don't think it needs a new fuel filter, i would go ahead and do it anyways. No telling the last time it got changed from previous owner and they are only around 10 to 13 in price. But yeah i would go ahead with the O2 sensors as well. Just my .02

David

 

[HISSIN50]

Have you watched PIDs?

 

[desertcox05]

how can it be lean and have horrible gas mileage unless there's a leak

 

[Bad92GT]

how can it be lean and have horrible gas mileage unless there's a leak

exactly thats my point. The mileage is horrible but the plugs says its burning clean as a whistle. The fuel HAS to be going somewhere.

 

[Chythar]

Any chance you have a leak in your gas tank?

I'm interested in this thread as well, my gas mileage is around 12-14 city yet my plugs are nice & clean. But I won't hijack this thread, I'll just sit back and see what our community comes up with.

 

[Zero Signal]

I had a similar issue with mine that I could never quite figure out until I pulled the engine apart to find out ONE plug was bad. Oil leaked through the valve guides , gumming one of the plugs which caused the computer to think it was running really rich on the one bank and caused it to run too lean.

THEN I later hypothesized that the bad gas mileage was due to messed up injector timing after changing the cam. The fuel wasn't igniting. It was being lost through the exhuast valve during overlap, thus exacerbating the lean problem by making the EEC think it was way too rich. I have a TwEECer which confirmed this by reviewing the datalogs and cam specs. If you are running the stock computer and cam, this isn't an issue unless your cam isn't degreed correctly.

Also, did you check your timing?

 

[Bad92GT]

The tank has a small leak, I do know what. It may be larger then i can see, but of course its hard to see all in there. I'm replacing the tank soon anyway because of a hole that someone patched. I just don't know whats going on with it. All the plugs were clean, smell free, and the car runs great. The timing seems to be correct, I don't have an actual light but its running great now. It's interesting, it runs lean, the plugs are clean, no real large issues anymore after the IAC, but it just doesn't do very well on gas. I'll stick it on a timing light hopefully tonight to try and dial it in correctly, but I would guess its around 12-14 degrees from my previous experience with these cars. This issue just baffles me though.

 

[Bad92GT]

Also forgot to mention that I'm replacing the fuel filter tonight with a motorcraft to see if it helps. Another thing is that I run only 93 octane shell premium in it. I run only shell in all of my cars, and none of them have noticed a decrease in mileage from the late gas price drop and water in the gas issues. This car has been getting, and continues to get, 10-12mpg pre and post the drop lol.

 

[Touring23]

My two cents: The speedo/odo is out of calibration. Drive it a few miles on a highway and compare mile markers against your odometer.
Hope this helps. Good luck.

 

[Labora]

My two cents: The speedo/odo is out of calibration. Drive it a few miles on a highway and compare mile markers against your odometer.
Hope this helps. Good luck.

I was kind of thinking that his math was possibly off one way or another also.

 

[Bad92GT]

well my ranger and my mustang have the same size gas tank. I drive the same amount every day and the gauge goes down a whoolllee lot faster lol. I burn a 1/4 of a tank going to work and back which is about 50 miles.. lol