Violent "lurching" when slowing down

[xj88RoKK]

I have an 87 comanche I just picked up in December. I have not modified or changed anything on the truck. Its a 2wd 4.0 long bed automatic. I bought the truck to clean up and give to my girlfriend, it seems I got her hooked. It's a southern truck with no rot anywhere.

I've put about 500 miles on the truck since I purchased it. It sat for 2 weeks while I was on vacation.

The truck runs and drives fine, except for this new issue that seemed to just pop up. If I am driving down the street at around 30 mph and I roll to a stop, it will "lurch" forward and back severely. Its not when I am accelerating or braking. It is when the truck is rolling on its own momentum. It is not after I hit a bump or turn. Its every time it slows from ~30mph - 15mph. I believe its in second gear when it happens. If I hit the accelerator slightly, it corrects the problem. If I ride the brakes a little, it corrects the problem.

Previous owner did motor mounts, trac bar and sway bar links, from what I see.

Any ideas? I would like to make it a little nicer to drive before I tell her I bought it for her. Thank you!

 

[MoparManiac]

Do the trans shift points work off the TPS? Does it drive fine other than that?

Could be a misadjusted TPS.

 

[xj88RoKK]

This is the first Comanche I've owned. It seems to drive along just fine. The only thing I've noticed since day one, is that it shifts early compared to the XJ's I've owned. I've owned stock autos and manuals, autos and manuals on 33's with 3.55's. All of which were 4.0's. It still seems to me that the MJ (also 3.55's and a 4.0, however my first Renix) seems to shift early and isnt as "peppy" as the XJ's.

 

[foxwar71]

Could be the torque convertor not unlocking correctly. Gives it that bucking feeling like a manual because its still locked up and not free spinning like it should.

 

[xj88RoKK]

Bucking is the word I was looking for. Lurching is all that came to mind. It really feels like I am braking then accelerating then braking etc. I was hoping it wouldn't be a trans issue. Was hoping for a trans mount or something like that.

 

[87manche]

a few things.

check the TPS
Check the TV cable to the trans
Power or Comfort mode?
Check the driveshaft u joints.
Check the pinion bearings.

all of those things could lead to bucking on decel. It's worth noting that while in decel mode the renix ECU cuts all fuel. So a maladjusted TPS could lead to it popping in and out of decel mode.
see here for TPS adjustment
http://www.lunghd.com/Downloads_and_Links/Adjusting_TPS.zip

 

[xj88RoKK]

Thanks for that link. I'm going to check the voltage now, I'll report back later on tonight

(this is in comfort mode) I've never had it in power mode before

 

[kastein]

Power mode behaves just like the later models act normally. Comfort mode is granny mode / scare you because you think the trans is slipping mode. At least it was for me after I bashed the switch with my knee by accident one day.

 

[87manche]

Power mode behaves just like the later models act normally. Comfort mode is granny mode / scare you because you think the trans is slipping mode. At least it was for me after I bashed the switch with my knee by accident one day.

this.

put it in power mode and forget it. Or just jump the wires permanently and repurpose that switch for something else.

 

[cruiser54]

After checking the driveline for looseness, I'd click on the link below and do posts 1 through 5, maybe even #27 and address the largest known issues with Renix in just a couple of hours. Get that stuff behind you.

BTW, how is the tuneup hardware? Pulled a plug or looked inside the distributor cap? Wires brittle and old?

http://www.cherokeeforum.com/f51/cruiser54s-mostly-renix-tips-153657/