Looking for some help. I have a 1994 blazer4.3 AT 4x4 with no 4x trans case. I put a junkyard trans in and it worked about a week. Now when it warms up it wont shift out of second gear. It cools off overnite and it works ok till it warms up again. Any ideas

 

Please clarify the situation a bit. What do you mean when you say "with no 4x trans case"?

Are you sure that you only have 2nd gear? What happens when you manually pull it into 3rd, 2nd, or 1st?

The 4L60E will default to 3rd gear starts if it loses power/ground. The fact that it is only when it's warmed up seems like it may be an hydraulic issue, but I have seen some wiring faults that show themselves only when the drivetrain has come up to temperature as well.

 

4x transfer case not hooked up.when I manually shift nothing happens it just stays in second gear.

 

its going into limp mode for some reason. my 93 does the same crap. in my situation it was something in the pcm not telling the transmission to go into the right gear. it used to do it randomly and shutting the truck off for a hour or less would fix the situation for a few hours until it finally went into 2nd and stayed there for good.

unfortunately i dont know how to tell you to fix it for good as my truck only sees offroad so i grounded the solenoids that needed to be grounded to get first gear back and thats all i wanted. but yeah it was some kinda goofy computer issue

also the other issue i have is i randomly blow my ign/gau fuse under the dash about every 4 hours or so which again will throw my transmission back into 2nd so maybe check that fuse and see if thats the problem

 

Please specify:

Does your Blazer have the remote oil/water intercooler?
If yes when changing the automatic transmission there may be a need to bleed the hydraulic oil system.

Questions to all:
Could that relate to the tranny working when cold as the oil will drain back to the pan but when warming up being gradually pumped out into the air pocket somewhere in the cooler lines and radiator?