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88 Comanche Chief Auto Not Shifting

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Hey Guys,

I have a 1988 Comanche Chief short bed 4x4 with the 4.0 and automatic transmission. I've owned it for a few years now and use it as my daily driver, fixing it up little by little.


Hopefully someone can help me diagnose this shifting issue.


When put into Drive, it feels like I'm trying to take off in 3rd gear. Very weak taking off.


But if I shift it manually on the floor shifter, the numbered shifts seem to work fine and I can spin my tires if I floor it at a takeoff in 1st.


So far I've cleaned up the NSS (Neutral safety switch) and it solved the reverse light problem I had had no effect on the transmission shifting.


Curious about this Trans Control rocker switch that I have on the dash which the plastic rocker is cracked. Could that be the culprit?


Also saw a few youtube videos about the throttle control cable, but it didn't change anything.


Possibly an issue with the Transmission Control Module (TCM)? I have it accessable under the dash on the passenger side. If you guys are thinking TCM, suggestion on fixes? Or replacements?



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Thanks for the quick response.

I checked it before posting, I should have mentioned that.


It is getting power and fuse is good. 10Amp fuse if I remember correctly.


I also changed the shift solenoids and changed tranny fluid.

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On 12/11/2020 at 7:59 PM, cruiser54 said:

TCU could be bad.


ever completed Tip 10 on my website?

tip 1?

Thanks Cruiser, first I'd like to thank you for your comprehensive guide. I actually just stumbled on it a few days ago and I've been going through it.


I checked the fuse, cleaned the connectors and checked power going though the fuse. All that was good. I don't remember checking for that connection that goes to the NSS but I do know that my dad removed my NSS and we cleaned it up (fixed the reverse lights, now they work). And my dad is very thorough so I THINK that connection was good but I will have to take a second look this week.


Can you explain what this dash rocker switch that says trans control is?

I saw a way to bypass it a long time ago but never tried.


I should also probably mention that a few wires behind the dash were melted together when I bought the jeep, I've done a lot of wiring repairs through the dash and in the engine bay. Previous owner just kind of added wires and switches to God knows what.


Gas tank leaked so I replaced it, also replaced fuel pump and the 3 solenoids in the transmission. All working properly now, except still not shifting as it should, seems like it just prefers to start and stay in a higher gear (I'd say 3rd gear) when in Drive. Takes off like a pig. Manual shifts work great though so I know the cable is working.


Since day 1 I've had this shifting issue, I definitely think it's an electrical issue. Either bad TCU or something with this trans control switch, or a bad ground that I haven't found.


Really wanted to just throw an AX15 in here but I need this auto to work because all my other jeeps are manual and I need my wife to be able to drive me home from the bar 😅

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1 hour ago, cruiser54 said:

The dash switch will not affect it starting in a higher gear. I'd find a used TCE from an 88 to 90 and plug it in. 

This is what you're talking about right?

Found it on eBay, I think it should be right for my truck.


Also attached a picture of the one I have now.






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