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Q:

wont shift gears form low on 1990 Mercury Grand Marquis

Enthusiast 01be16a5a93688912f14755221fb15211b518d9a788cf01b455e03cc1bd585ac
this is the second tranny i am putting in it will not shift form low gear when driving there is no modulator on it but i have changed the speed control sensor i was told there may be a computer somewhere that controls the shifts if so where if not what controls the shifting it has a 5.0l eng. and a aod tranny automatic
(2) Answers
check your map sensor. some of those years have a maf for the engine & a map for the tranny. if no map, clean the maf because the map in later years is computed from maf.