Puzzling 4l60e

a_kelley

mechanical fixer
Joined
Jan 26, 2010
Location
Rutherfordton
Ok so my buddy has a 93 Jimmy, 4.3 4l60e 4wd.

When you start it, engage 1st fear, but only one time. (He says it doesn't have overdrive either). After it shifts out of first, it will not go back into 1at, whether manually shifted or automatic. If you shut the vehicle off, And restart it, it will engage first, one time. It was a rebuilt trans with not many miles since the rebuild. I'm going to dig into it in the next few days, but I'm suspecting that the manifold pressure switch is the problem, since that model relies on the pressure switch to indicate shift lever position. (If it were to report 3rd gear selection would prevent OD, but not 1st). Shift solenoids have been replaced - and are not the issue - since if either solenoid were malfunctioning he wouldn't have 2-3 shift as both change states for that shift to occur. Tried swapping pcm but we had difficulty locating a correct unit with correct programming since it's a 2 year product (93 & 94 only, Central port injection and non pwm converter)

Any recommendations on what to check? I'm familiar with valve bodies and operation - just hoping someone has had this issue before.
 
Thinking maybe the manifold pressure sensor - there's no shift level position switch, but he hasn't had time to drop it off yet. That or it's a valve body issue with a cross leak or check ball getting stuck..
 
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