hey everyone.. thanks for reading my twilight zone truck. i desided to start a new post and inform you everything i have done:
as you know, i have been getting this sporadic p0155(then a 0174) error code(running lean) on my obdii bronco. this original engine has NEVER BEEN TAKEN APART FOR ANYTHING!!! i baby this thing.
it is a 96 351w(188,700 miles) with mass air. i still get this code when i have done the following:
1. replaced the 02 sensors(lst summah) (still can't find the fuse if there is one)
2. replaced the fuel filter.
3. replaced the air bypass valve. (the original looked BAD.)
4. have run one and a half tankfulls of fuel injector cleaner(stp and lucas)
5. changed the spark plugs.
6.checked the vacuum. it is normal.
7.removed the mass airflow meter and hosed it with MAF cleaner, big time.
8. i bought a new fuel pressure regulator, not installed yet. gonna let the pressure drop over night and get to it tommorrow.

does the regulator go bad to the point where is dumps fuel back into the tank? i have heard of them dumping more fuel into the engine causing it to run rich, not lean. my gas milage is crappy. and recently i reset the cpu by disconnecting the battery. upon test driving it, at one point, the truck suddenly lost power, wheter i was going up hill or down(idling down) and then the truck suddenly "picked it up" it was as if the CPU was learning that i needed more fuel. it drove fine after that untill i shut off the truck after 10 miles and the stupid check engine light came back on. sigh.

 

i would buy new o2 sensors from ford. have you gotten rid of the platinum plugs yet? have you checked the fuel pressure at the rail?

 

actually, i gave up. My mechanics says there is a ford dealership TSB on the wiring harness. he used to be a ford mech. and has his own shop. he gets the same tsbs the dealers get that we don't. a faulty voltage problem on the wire harness causes it to have this code p0155. his words. i told him everything i did and to no avail did the problem change. i wasnt worried about the spark plugs because i have a accel supercoil on the truck. beleive me, i tow a formula 272 with twin 350s and this thing can TOW!! everything i have done to the truck has given me more power and better gas mileage.. until now. Summah is coming!! i an't fiddling with this any longer!! thanks for your responses everyone!!