hello all, I have a 93 f150 L6 4.9 w/ the 5 speed mazda tranny. for the longest time it has been running incredibly rich. i used the eec 4 self test and and pulled the following codes which i believe stand for:

key on engine off:
125: TP (throttle position?) voltage was lower than expected

key on engine on:
126:MAP sensor out of whack.

998: bad computer

so i opened up the computer and found that a capacitor had started leaking, i replaced it but apparently there was other damage because it still pulled the same codes.
so i just spent $170 on a new computer and installed it about 10 minutes ago
and got THE SAME CODES!
now since this is a completly new unit it seems that there would be no "memory" and that these codes are still a problem.

i did buy a new TPS at one point but i compared it to the old one with an oscilloscope and they were identical so i returned it, and i have replaced the MAP sensor twice.

let me tell you the symptoms:
1. truck idles high ALWAYS.
2. truck runs EXTREMELY rich ( i am getting <12 MPG and lots of black smoke)
3. when the throttle is depressed to a certain extent, whether in gear or not, the engine grossly misfires. if it is in gear the thing nearly stalls as if the engine has completely cut out, and jeks wildly. (this i think may still be the TPS some how)
4. when the engine is idling, as soon as you first touch the gas pedal the rpms drop for a split second, pretty much like a misfire every time you touch the gas pedal from idle.
5. it's costing me lots of money to fill up every 5 days.

any help would be greatly appreciated. THANKS.

 

Fuel pressure regulator?

 

You probably would have spent less money taking it to a good shop. It does sound however, like you might have a voltage reference issue or a bad ground, couldn't hurt to check.