JeepForum.com

JeepForum.com (http://www.jeepforum.com/forum/)
-   ZJ Grand Cherokee Forum (http://www.jeepforum.com/forum/f13/)
-   -   93 ZJ 4.0L/AW4/249 "Slipping" at highway speed (http://www.jeepforum.com/forum/f13/93-zj-4-0l-aw4-249-slipping-highway-speed-1216852/)

93zjer 05-20-2011 12:42 PM

93 ZJ 4.0L/AW4/249 "Slipping" at highway speed
 
While driving over 45, and especially when not under acceleration or load my jeep will jump about 250-500 rpm (rpms go up) and I can feel a loss of power.
It only does this for a second ,literally, or maybe two, then rpms drop down to normal and its fine. It is intermittent. During a 1700 mile road trip it happened around a dozen times. Has not thrown any codes and runs very well other wise.

General_Jeep 05-20-2011 01:12 PM

how many miles are on this Jeep?

savannahzj 05-20-2011 03:19 PM

mine does the same thing, usually with the cruise control on, above 55, it will jump about 200 rpms and then jump right back. mine is more like an rpm surge, so i was thinking tps.

freakinheep89 05-20-2011 05:41 PM

sounds like the converter is unlocking/locking back in suddenly.

When you are even on the throttle and the TC lockup clutch is engaged, its a 1:1 drive. if the converter unlocks unprovoked(without you stomping the gas) the converter will slip a bit and the RPM will surge. I would start looking for anything that could be causing the converter to unlock randomly, like the TPS.

93zjer 05-21-2011 02:19 PM

the jeep has about 220,000 miles but i took the engine out of a 95 ZJ that only had 60,000.
It ran with no problems for about a year then this started happening.

I thought the torque converter was unlocking but I noticed when the problem happens the RPMs only jump about 250-500rpm and when I use the gear selector the put it in third the jump is significantly more like 500-600.
Fourth gear is just the lock-up torque converter right? So I figured the difference in RPMs should be about the same if that is the problem I'm seeing is the torque converter unlocking for a second.
Is this line of thinking flawed?

Candymancan 05-21-2011 04:02 PM

Well 3rd is under overdrive, thats why the jump in rpm is higher, your turning overdrive off.


If you want to know for sure if its overdrive or the torque converter, simply drive the vehicle until the torque converter locks, then while your on the gas push the brake pedal slightly with your other foot and the torque converter should unlock. Take note of the rpm change and compare notes

freakinheep89 05-21-2011 07:58 PM

Quote:

Originally Posted by 93zjer (Post 11580437)
the jeep has about 220,000 miles but i took the engine out of a 95 ZJ that only had 60,000.
It ran with no problems for about a year then this started happening.

I thought the torque converter was unlocking but I noticed when the problem happens the RPMs only jump about 250-500rpm and when I use the gear selector the put it in third the jump is significantly more like 500-600.
Fourth gear is just the lock-up torque converter right? So I figured the difference in RPMs should be about the same if that is the problem I'm seeing is the torque converter unlocking for a second.
Is this line of thinking flawed?

Fourth gear is overdrive, then theres TC lockup. TC lockup is not overdrive.

Dropping the selector down a gear takes it out of overdrive, as candyman stated, causing the RPM surge.

the drop in RPM during lockup is about 250-300rpm on my 5.2.

93zjer 05-21-2011 09:14 PM

OK, I thought that might be wrong, thnaks
So the fourth gear is referred to as overdrive meaning a 1:1 or greater ratio.
The torque converter "locks up" to sort of bypass the normal fluid coupling way it normal transmits power allowing for greater fuel efficiency?

I think I'm going to lean my IAC and replace the TPS.
I have the test procedure for the TSP but given the intermittent nature of my problem i doubt it would test bad.

freakinheep89 05-21-2011 09:22 PM

Quote:

Originally Posted by 93zjer (Post 11582036)
OK, I thought that might be wrong, thnaks
So the fourth gear is referred to as overdrive meaning a 1:1 or greater ratio.
The torque converter "locks up" to sort of bypass the normal fluid coupling way it normal transmits power allowing for greater fuel efficiency?

I think I'm going to lean my IAC and replace the TPS.
I have the test procedure for the TSP but given the intermittent nature of my problem i doubt it would test bad.

Now you got it:thumbsup:


All TC lockup does is take the slip out of the converter and go from a fluid coupling to a mechanical lock.



As for the IAC, all that would do is create idle problems, typically they dont have any effect on driving unless they are stuck wide open.


One way to test the TPS(and the only real way, IMO) is with an analog volt meter to test the sweeping motion of the sensor. it should have a nice smooth sweep in voltage from idle to WOT, that cant be measured accurately without a needle to watch it sweep. if its jumps erratically its bad.

93zjer 05-21-2011 10:18 PM

Thank you!
I completely understand.
I'll post my result here after I test.

93zjer 08-09-2011 10:08 PM

It was my TPS. Replaced it and never had the issue again.

cootertwo 10-12-2013 10:09 AM

On my 97 GCL my bad brake light switch was causing my TC lockup to go in and out.


The time now is 09:49 PM.

Powered by vBulletin Version 3.8.4
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.