Red92cherokee

So ive had this problem now for about 3 weeks (one of which the jeep was undergoing a transmision swap) right before i replaced my tcase the jeep would buck real bad almost like a slow rev limiter but only in 3rd gear when i went past 3k as if to pass or get up to speed. After replacing the tcase i drove home about 90 miles and went easy so it was fine. Replaced the speed sensor on the tcase the next morning and seemed fine but when i got on the freeway i blew the tranny (thinking just the pump) did great all day after the swap was finished then started doing it again on my way out of town. Is it actually the speed sensor going bad or is something else wrong and if so what could it be. Turn key i get 12 (obviously then 62 then the final 55. The ecu is relatively new as in not used much but its a fes years old. Gonna test in the morning to see if unplugging the tcm and shifting manually gets rid of it bug putting the shifter in third seemed tk do the trick without unplugging today. Thanks in advance and sorry for the novel lol.

Red92cherokee

So i tried unplugging the tcm with the engine off and it doesnt change it, only in third and only after 3k rpms

318SixPack

You don't say what year.

If it has a single coil, check the connector and harness from coil to PCM. Especially the lock on the connector.

Red92cherokee

Ill check that here in a bit, and it’s a 92 laredo with the 4.0 and aw4 231 amc transfer case (the swapped one)

318SixPack

Should also mention to check the harnesses from crank sensor, pickup coil, and upstream O2 sensor.

But this sounds like coil, i.e., the PCM signal getting degraded enough that you notice the issue above 3K

Red92cherokee

Connections all looked good just now, i have em all a squeeze to make sure they were all the way in. Might get a coil today as well as a speed sensor

Red92cherokee

Just replaced the speed sensor and it fixed it but after about 8 miles tge speedo started going weird again but still no bucking

318SixPack

New one for me. Never touched my speed sensor.

Maybe take a multimeter to both ends of the wires to check continuity and condition of the pins.

Red92cherokee

That’s a good idea, ill go ahead and do that tomorrow thank you

cruiser54

To all users of CF:

PLEASE, before posting technical questions, take some time to help others out, by adding details in the user control panel. There's 2 ways to do this. First, in the upper left corner on the front page of the site, is a menu button labeled UserCP.




After you click on that you'll see this menu:





Please take the time to click on the highlighted sections and fill out the vehicle information for your vehicle. The signature link is also helpful for any additional information like mods done, links to your build or other vehicles owned.

This helps EVERYONE out by informing them immediately about your year, make, model, etc.

These details are necessary for responders to accurately answer your questions without guessing or having to ask what are the specifics of the vehicle you are referring to. You can add these details easily and permanently by creating a signature or adding your truck details to your existing signature.

5 minutes of your time doing this now will save a ton of time and effort later.



Thanks!!!

Red92cherokee

I apologize, it’s all filled out n

cruiser54

No apology necessary. Glad it's done. It helps us to help you.

Red92cherokee

Completely understand