Copying/Pasting this from a local forum...

Problem Statement: Excessive fuel consumption.

Knowns:

1. Ford Motorsport 42 lb Injectors. These are scaled appropriately and include the Flow Rate vs. kPa, Short Pulse Limit, Short Pulse Adder, Injector Offset vs. Volts vs. Vacuum.
2. Fuel pressure verified at 54 psi with the ignition on and 59 psi while the engine is running.
3. Disabled Closed Loop and the Mass Airflow sensor.
4. AF is extremely lean when in open loop (18.9 – 19.7 AFR).
5. The car idles fine once the AF is richened up. The IAC steps are ~60 Hot and the STIT is in an acceptable range. The LTIT is -3.00 and will need addressed.


Upon logging the vehicle, the car drives much better in Open Loop and with the MAF disabled. I used some starting fluid around the intake area and no rise in engine rpm. Also, I checked AF both headers and the drivers side is not as bad as the passengers side. Check the headers bolts and a few of them loosened up. This is more than likely due to heat cycling. Noticed the both header flanges are warped. There are gaps between the flange and the cylinder head and the exhaust gasket can be moved with a screwdriver. I can post pictures once my wife returns home with the camera. I am leaning towards the headers needing replaced and always open to opinions. Maybe we all can partake in some technical discussion.

Recommendation:

Replace the Longtube Headers.


Do you guys agree, that swapping the headers out would fix my problem? I just want some more opinions before I buy them. Again, I can't stress enough that all these problems began after my fuel pump/filter/pressure regulator were changed. And my Fuel Pressure lowers under acceleration.

Here are some pics of the flanges...

 

If you're now in open loop, replacing headers won't really affect your fuel economy unless there's some major blockage. I'd suspect an injector fuel delivery or an ignition problem (dead hole). Changing headers won't solve your problem, but if you have leaks, new headers will make logging A/F with the wideband more accurate.

 

as embarassing at is sounds my headers are in worse shape and i have had no problems like yours

 

Those really aren't that bad, I've seen way worse on cars that were making 20+ mpg. Don't really know how an exhaust leak could make that bad of a mpg by itself and I am sure you would hear one that bad and see soot all over your heads where the leaks are present. Throwing any code?

 

How far does your pressure drop when under acceleration? If I remember correctly the pressure should never drop below 58 psi or there might be an issue. I am not really sure how that would work out to 6mpg but at least it would be a place to start looking. IMO replacing your headers will not have a significant effect on your problem. For you to be getting 6mpg something with the actual fuel system itself, or the delivery of fuel is the problem.

 

So basically it runs like crap, reads lean and burns a ton of fuel. That sounds like the 02 sensors are biased lean making the computer think you are running lean and compensating for a lean condition by adding fuel to the mixture which results in high consumption, also in which case will cause it to run like ****. First thing I would do go in the datastream and look at Long and Short term fuel trims with a scanner if you have one to see if it is over compensating, then I would look at the 02 sensors in the datastream and make sure they are capable of reading the capable range they are supposed to and that is generally 0.1 volt to 0.9 volt. If you have a narrow band air fuel guage in your car it should swing back and forth at idle and cruising speed, that shows the 02 sensor swing and indicates they are capable of reading the range they are made to read. But im going to assume you have used a wideband since you stated you saw around 18-19:1 AFR.

You could have a leaking injector, you could check this by pressurizing the system with a fuel gauge installed and crimping off the fuel feed line going into the fuel rail, the pressure should hold.. It should not drop if it does you have a leaking injector or did not get the line crimped all the way.

You can also pull the fuel rail up and pressurize the system and watch to see if an injector or more than one leaks. Be cautious not to crank the car with the injectors pulled up and out I have seen a fire started like that before, you could unplug them and the coil pack connectors as a safety measure if you do check them this way.

Thats a start, hope it helps.