Fuel issues

[Thoroughbred]

When I drive the ole stang around with the fuel pressure at the stock psi 39...the check engine light will come on and it throws codes that says both banks are Lean. This is not close to being true, from that if you stand behind the car your eyes will start burning from the exhaust fumes very shortly. The car seriously seems to be almost belching raw fuel. Something else that is interesting is that when you turn the car on to go somewhere, the check engine light is always off and comes on later.

I tried turning down the pressure down to 35. Since I thought there is no way this thing is really 'lean' and there are no 'rich' codes. I was pondering that the comp see's it running really rich and its trying to lean it out but its reached a point to where it wont lean it out anymore and so its throwing this lean code at me. So I turned down the FP and the light came back on my first trip out But has not come back on since.

The car has spankin new O2's less than 2 weeks old, new IAC, my MAF voltage is at 1 volt at idle...according to ProM's new website under their Tech section. If ur voltage is between .2-1.5, at idle, by probing terminals C&D your Maf should be good to go. My fuel system is a 255 intank, Kirban Adj FPR and 24's. Not neccessarly anything extreme there.

I have this complete fuel system as is for well over a year now..maybee even two? The check engine light came last week or so.....I unhooked the Bat over night after I put in the new O2s....Fuel filter is less than 10K old...Spark plugs are less than 2kish.

Anyone have any ideas?

[red95gts]

I'd look for a vacuum leak.

The way it works is the MAF will measure the mass of the air entering the intake tract. It will use that measurement to calculate the fuel demand for a given airflow. The O2s are in place as a check and balance to make sure the fuel requirement estimations are correct. In a properly functioning car, it goes like this:

O2 reads lean
EEC richens mixture
O2 reads rich
EEC leans mixture

....and so on and so on. In a properly operating system, the output from the O2 will "switch" around the stoichiometric point (14.7:1). The fact that you are getting a lean error code tells you that one (or both if codes 41 and 91) sensor(s) are not switching - they are pegged lean.

A vacuum leak downstream from the MAF can and will cause this since there will be "extra" air in the mixture vs. what the MAF measured. Check the EGR diaphragm, upper to lower gasket, etc. PCV and vac lines are always a suspect as well.

Also, check that the O2 sensors are getting the 12V switched to operate the internal heating elements. Although, if memory serves, this will make the sensor read rich (not lean) all the time since it never heats up to operating temperature. But, it's worth looking at.

Also, exhaust leaks can do the same thing (assuming they are upstream from the O2).

Hope some of this helps!

[HoustonLX]

Darrell...ASSuming there is a vacume leak and the O2's are reading a lean condition there by attempting to richin the mixture, could this problem also cause poor gas mileage? Only reason I ask is cause my car gets horrible gas mileage even with the stock H/C/I and injectors. I also get stoned from the smell of gas when driving with the windows down.

/me turns thread whore mode <OFF>.

[Thoroughbred]

I shall see what I can find and post back later

[Thoroughbred]

Ya know that cluster of Vac lines on the passenger side, that all go into one connector. And then they split off going to the egr, upper intake and 2 go to ur air pump piping crap.
Well thats been a lil getto rigged for a bit and I thought it was okay but I think it needs to go. A friend that works at a ford dealership tryed to locate this for me but Ford doesnt make it anymore. So I'll try to get one off another Fox somewhere. Also replace the PVC just cuz its cheap.

Ill take a pic and post it later of those lines. Dam you ford and ur infernal vaccum.