tylergrant2011 Posted February 28, 2022 Share Posted February 28, 2022 I have a 87 A/T MJ that whenever I go to put it in drive, it seems as if it is in 3rd gear. It only will move at high RPMs. If I put the truck manually in 1st gear, then it goes fine. I havent checked anything except the inline fuse link on the passenger side located near the TCU and of course the transmission fluid. Does anyone have any ideas of what the problem might be? Is there a way to check the TCU like what the incoming voltages should be? This truck only has 90k original miles. Also it hasn't been drove in almost a year. Link to comment Share on other sites More sharing options...
Ωhm Posted February 28, 2022 Share Posted February 28, 2022 TCU fuse (7.5A). Fuse block. Link to comment Share on other sites More sharing options...
cruiser54 Posted February 28, 2022 Share Posted February 28, 2022 10 hours ago, tylergrant2011 said: I have a 87 A/T MJ that whenever I go to put it in drive, it seems as if it is in 3rd gear. It only will move at high RPMs. If I put the truck manually in 1st gear, then it goes fine. I havent checked anything except the inline fuse link on the passenger side located near the TCU and of course the transmission fluid. Does anyone have any ideas of what the problem might be? Is there a way to check the TCU like what the incoming voltages should be? This truck only has 90k original miles. Also it hasn't been drove in almost a year. How did you check the fuse? That is the main power for the TCU, Have you ever visited my website and completed Tips 1 through 5? 10 would be a good one to complete also. That TCU grounds at the most problematic ground point on your Jeep. Link to comment Share on other sites More sharing options...
tylergrant2011 Posted February 28, 2022 Author Share Posted February 28, 2022 39 minutes ago, cruiser54 said: How did you check the fuse? That is the main power for the TCU, Have you ever visited my website and completed Tips 1 through 5? 10 would be a good one to complete also. That TCU grounds at the most problematic ground point on your Jeep. I pulled the fused and tested for continuity. I'll check the block where the grounds are and make sure they are clean and tight. Link to comment Share on other sites More sharing options...
cruiser54 Posted February 28, 2022 Share Posted February 28, 2022 You could also check for voltage at the fuse while you're at it. Link to comment Share on other sites More sharing options...
tylergrant2011 Posted February 28, 2022 Author Share Posted February 28, 2022 1 hour ago, cruiser54 said: You could also check for voltage at the fuse while you're at it. Should I get 12v at the fuse? Also which wire is the ground wire for the tcu? Link to comment Share on other sites More sharing options...
cruiser54 Posted February 28, 2022 Share Posted February 28, 2022 Pretty sure it's 12V. All the ground wires on that dipstick stud are black. You want the ground terminal AT the TCU? D3, D7, C5 Link to comment Share on other sites More sharing options...
tylergrant2011 Posted February 28, 2022 Author Share Posted February 28, 2022 5 hours ago, cruiser54 said: Pretty sure it's 12V. All the ground wires on that dipstick stud are black. You want the ground terminal AT the TCU? D3, D7, C5 Yes I wanted to back probe the grounds at the TCU connector and measure the resistance coming off of it. Link to comment Share on other sites More sharing options...
tylergrant2011 Posted March 1, 2022 Author Share Posted March 1, 2022 11 hours ago, cruiser54 said: Pretty sure it's 12V. All the ground wires on that dipstick stud are black. You want the ground terminal AT the TCU? D3, D7, C5 I cleaned all the grounds. I added an extra ground at the engine to the frame. I moved the main ground away from the dipstick tube and bolted it on the side of the block just up from the dipstick. The small black wires I put at the dipstick tube mount which is where they were originally and that is piss poor placement for a ground in my opinion. Also I checked the connector that goes to the TCU. All of the ground terminals at the TCU are around 0 ohms. I tested the voltage on both sides of the fuse and it was at 14vdc. I'm gonna attach some photos and hope you can tell me where to go next with this. When you look at the photo of the small black grounds tell me what that connector is just to the left of it. Link to comment Share on other sites More sharing options...
cruiser54 Posted March 1, 2022 Share Posted March 1, 2022 That isn't factory.... The TCU may be bad. It happens. You can grab a TCU from any 88 through 90 Cherokee or Comanche. Link to comment Share on other sites More sharing options...
tylergrant2011 Posted March 1, 2022 Author Share Posted March 1, 2022 10 hours ago, cruiser54 said: That isn't factory.... The TCU may be bad. It happens. You can grab a TCU from any 88 through 90 Cherokee or Comanche. So any renix era xj or mj will work correct? Link to comment Share on other sites More sharing options...
MiNi Beast Posted March 1, 2022 Share Posted March 1, 2022 Yes Link to comment Share on other sites More sharing options...
cruiser54 Posted March 1, 2022 Share Posted March 1, 2022 88 and later are more desirable. Link to comment Share on other sites More sharing options...
tylergrant2011 Posted March 2, 2022 Author Share Posted March 2, 2022 3 hours ago, cruiser54 said: 88 and later are more desirable. Can you tell me where that single prong connector goes just to the left of my grounds on the dipstick tube? I'm gonna head to the junkyard and grab a new TCU out of a 89 and update if that solved my problem. I might grab the ecu while I'm at it. Link to comment Share on other sites More sharing options...
cruiser54 Posted March 2, 2022 Share Posted March 2, 2022 Good plan!! That wire is likely for the underhood light. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now