Terrible mileage -I need a plan of attack.

[stock50LX]

Terrible mileage, Where should I go from here?

My 351 with long tubes gets terrible mileage. The check engine light comes on after the engine warms and the numeric codes translate to "lean condition" for both banks. I conclude that the computer is richening the mixture based on that signal. I swapped he oxygen sensors with my other car and that made no difference, so those can be ruled out. Please read the signature for additional info. The car has 24 pound injectors and an A9L computer. The Pro M is very old but it shows that it is calibrated for the 24's. The car has no air pump and the EGR is not connected to any vacuum line -but if I do connect the EGR, there is no change. This car also has a lopey cam.

I've been correcting problems since I bought this thing, this is just another issue. It's an interesting contrast with my other Fox body that never has any problems.

Thanks in advance. Any advice is appreciated. I am not certain where to go from here, except maybe to a carburator.

 

[stock50LX]

Someone must have a suggestion. This thing might just as well be carbed given its current mileage.

 

[ECU5.0]

if its running lean, put a fuel pressure regulator on it and crank up the pressure. but it shouldnt be getting terrible gas mileage just because of a lean condition..but its something to try to fix it

 

[jrichker]

The lean codes show that the O2 sensors aren't up to snuff, or are mounted too far away from the exhaust valve. The O2 sensors have an optimum temerature that they run at. Long tube headers loose much of the heat required to make O2 sensors work properly.

Make sure that the O2 sensor heater circuit is working properly. If it is, then the O2 sensors are mounted too far away and are not getting hot enough to do their job. Some new O2 sensors followed by some header wrap would be the thing that I would do.

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)

http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif

 

[stock50LX]

The lean codes show that the O2 sensors aren't up to snuff, or are mounted too far away from the exhaust valve. The O2 sensors have an optimum temerature that they run at. Long tube headers loose much of the heat required to make O2 sensors work properly.

Make sure that the O2 sensor heater circuit is working properly. If it is, then the O2 sensors are mounted too far away and are not getting hot enough to do their job. Some new O2 sensors followed by some header wrap would be the thing that I would do.

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)

http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif

WIth the long tubes, I am certain that the O2 sensors are too far away. The diagram didn't help me. How would header wrap help the 02 sensor perform better?