93 ZJ 4.0L/AW4/249 "Slipping" at highway speed - JeepForum.com
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Unread 05-20-2011, 01:42 PM   #1
93zjer
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1993 ZJ 
 
Join Date: Jan 2010
Location: Humboldt, California
Posts: 317
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.

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Unread 05-20-2011, 02:12 PM   #2
General_Jeep
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how many miles are on this Jeep?
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Unread 05-20-2011, 04:19 PM   #3
savannahzj
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1998 ZJ 
 
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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.
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Unread 05-20-2011, 06:41 PM   #4
freakinheep89
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1995 ZJ 
 
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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.
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TJ-
[SIZE="1"][B]95 ZJ 5.2[/B]- D30/XJ shafts/D35 Yukon alloys,249, 2"BB, 30x9.5"Wildcat EXT,lots of motor mods, rancho shocks & stabilizer.[/SIZE]

[QUOTE=slayercr23;12630497]How would i go about Stroking it?[/QUOTE]
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Unread 05-21-2011, 03:19 PM   #5
93zjer
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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?
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Unread 05-21-2011, 05:02 PM   #6
Candymancan
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1998 ZJ 
 
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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
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Unread 05-21-2011, 08:58 PM   #7
freakinheep89
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Quote:
Originally Posted by 93zjer View Post
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.
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TJ-
[SIZE="1"][B]95 ZJ 5.2[/B]- D30/XJ shafts/D35 Yukon alloys,249, 2"BB, 30x9.5"Wildcat EXT,lots of motor mods, rancho shocks & stabilizer.[/SIZE]

[QUOTE=slayercr23;12630497]How would i go about Stroking it?[/QUOTE]
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Unread 05-21-2011, 10:14 PM   #8
93zjer
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1993 ZJ 
 
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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.
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Unread 05-21-2011, 10:22 PM   #9
freakinheep89
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Quote:
Originally Posted by 93zjer View Post
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


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.
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TJ-
[SIZE="1"][B]95 ZJ 5.2[/B]- D30/XJ shafts/D35 Yukon alloys,249, 2"BB, 30x9.5"Wildcat EXT,lots of motor mods, rancho shocks & stabilizer.[/SIZE]

[QUOTE=slayercr23;12630497]How would i go about Stroking it?[/QUOTE]
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Unread 05-21-2011, 11:18 PM   #10
93zjer
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Thank you!
I completely understand.
I'll post my result here after I test.
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Unread 08-09-2011, 11:08 PM   #11
93zjer
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It was my TPS. Replaced it and never had the issue again.
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Unread 10-12-2013, 11:09 AM   #12
cootertwo
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On my 97 GCL my bad brake light switch was causing my TC lockup to go in and out.
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