zroth1992

For the past few months my 1998 mustang v6 3.8 liter has been running the codes po172 and po175 as running rich. The iat sensor reads correctly, the mass air flow sensor has been replaced 3 times, the fuel filter has been changed, there has been a tune up done, the fuel pressure regulator was changed, the vacuums and manifold have been checked for leaks, and the o2 sensors have been reading correctly. The car runs strong occaisoinally, but usually runs weak with soft bucking. When idling the cars short and long term fuel trims are in the negative and when at 2500-3000 rpms, the long term trims are at -20/-25 and the short term fuel trims are at 0/-8. What could still be wrong with the car? The mass airflow sensors were bought from autozone, not ford dealer.

10KonaBGT

Sorry I have no clue on that one. You might want to post this in one of the tech sections, probably get more traffic over there.

jwog666

ect sensor could be reading incorrectly telling pcm its too cold, pcm adds too much fuel, o2s pick up on it and your trims go negative. have you checked fuel pressure? it may be too high due to a restricted(kinked) fuel return line. check you baro pid (will need scanner) here in wisconsin we are at about 1000ft above sea level baro reads 156hz give or take 2hz, your correct reading will depend on your elevation. if baro is off fuel will be off.