I have a 91 f-150 with 5.0 and the ford mass air conversion kit. It has been fine for about 3 years now but for about the last 2 months my gas mileage has gone to crap. I did a complete tune up,including plugs, wires, o2 sensor and air filter. it didnt help much. I have hooked up my snap-on scanner and found no codes or problems on the power ballance test. I wish I could get a datastream from this computer to see exactly what all of the sensors are telling it but i havent figured out the proper codes to give the scanner for a vehicle id yet. the 5.0 in 94 and up explorers and some cars with eec-4 give sensor data so i figure this one should too. If anyone knows what i am talking about here and has a suggestion or wants more info please let me know soon this thing is getting a little expensive to feed. My wifes 73 buick with a 455 and a 4 barrel is getting better mileage lately. we used to be about equal.

 

 

I don't know how to get the sensor data but have you tried checking the fuel rail pressure. I believe the pressure SB about 41psi. My fuel pressure regular went and my lousy gas milage was the first thing I noticed.

John

 

Howdy Dan,

I've had a similar problem with my truck. 96 F250 460/E4OD No codes but will run like crap when it feels like it. I don't know if your truck would support a Data Flight Recorder, but I installed one to my Diagnostic Port and recorded the computers readings under load and no load. What I have found is the O2s would flat line while driving which would tell the CPU its in a Lean condition and would dump fuel (LITERALLY) in all cylinders. When this occurs my S-Trim would read "0" at the same time. Since I've done all you've done except install a new computer, (doing that tomorrow) i expect it is the culprit. There's nothing else really to change. All else checks out for me.

If you have a good repour with a dealer see if they will install a Data Flight Recorder to truck to see whats going on with the computer while you drive it. I'm not sure if your truck supports that but think it does. Probably will cost ya 75 bucks to have it hooked up and keep it for a day while you drive it. This was the only way I was able to see what the computer was doing.

You didn't mention if your truck pings while driving or not? Have you checked your EGR valve, IAC, IAT sensors?

It seems the EEC IV is one of the hardest systems to diagnose. I think this is true. I've been having this problem for about 3 months on and off. Hopefully the new CPU with correct my problem?

Did your truck come equipped with MAF or was it a aftermarket item?

I hope this helps

Xaviar