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Unread 05-21-2011, 07:12 PM   #1
stmprnch
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Vacuum or Electrics?

Howdy All

My ZJ runs pretty good these days but it has an intermittent problem that I'm not sure where to start looking for a solution.

Once in a while when I slow down at a stop light or just slow enough to pull inot a parking lot, where you would expect the engine to run at idle RPM, the RPM will slow down to almost a complete stall. The engine runs good enough that it doesn't die, but it is idleing so slow that the oil pressure drops to around 35 PSI. Turn it off and back on and the problem goes away. This leads me to think electrics, but I don't know the systems well enough to be sure.

Another symptom that might be related is at highway speeds, 60-70 MPH, the RPM will jump as if the torque converter is locking and unlocking. Again, I don't know the electrics in these well enough to know if the converter is being controled by a solenoid in the tranny or vacuum.

Any suggestions appreciated.

Ron

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Unread 05-21-2011, 10:00 PM   #2
TallyZJ
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Quote:
Originally Posted by stmprnch View Post
Howdy All

My ZJ runs pretty good these days but it has an intermittent problem that I'm not sure where to start looking for a solution.

Once in a while when I slow down at a stop light or just slow enough to pull inot a parking lot, where you would expect the engine to run at idle RPM, the RPM will slow down to almost a complete stall. The engine runs good enough that it doesn't die, but it is idleing so slow that the oil pressure drops to around 35 PSI. Turn it off and back on and the problem goes away. This leads me to think electrics, but I don't know the systems well enough to be sure.

Another symptom that might be related is at highway speeds, 60-70 MPH, the RPM will jump as if the torque converter is locking and unlocking. Again, I don't know the electrics in these well enough to know if the converter is being controled by a solenoid in the tranny or vacuum.

Any suggestions appreciated.

Ron
Torque converter or over drive is not letting go soon enough. Probably the over drive solenoid is acting up. Mine does this occasionally but has since stopped for some reason.

Nothing on your transmission is vacuum controlled. All electrical and line pressure.
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Unread 05-22-2011, 05:01 AM   #3
jr4x4
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replace the brake swich under brake pedel. my jeep was doing same thing at 55 & over almost felt like slipping. 2 tranny shops told me my tranny was going. 10 bucks & problem fix'd. & if your o/d isnt working it's usally that swich too.
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Unread 05-22-2011, 10:03 AM   #4
stmprnch
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Electrics Question

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Originally Posted by TallyZJ View Post
Torque converter or over drive is not letting go soon enough. Probably the over drive solenoid is acting up. Mine does this occasionally but has since stopped for some reason.

Nothing on your transmission is vacuum controlled. All electrical and line pressure.
So, I'm assuming that the O.D.S. is inside the tranny, I'll check my manual later today. Are there any electrics, M.A.P. sensor?, that that could get flaky and cause this?

What about the throttle control cable that runs back to the tranny? the plastic sleeve on mine seems to be in descent condition but I don't know if I would notice a problem with it.

Thanks for the info.
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Unread 05-22-2011, 04:46 PM   #5
TallyZJ
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Originally Posted by stmprnch View Post
So, I'm assuming that the O.D.S. is inside the tranny, I'll check my manual later today.
Yes. There is a good writeup in the drivetrain section or look in the FAQ


Quote:
Originally Posted by stmprnch View Post
Are there any electrics, M.A.P. sensor?, that that could get flaky and cause this?
Nope


Quote:
Originally Posted by stmprnch View Post
What about the throttle control cable that runs back to the tranny? the plastic sleeve on mine seems to be in descent condition but I don't know if I would notice a problem with it.

Thanks for the info.
Just do an adjustment as per the writeup. Search for TV cable adjustment
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Unread 05-22-2011, 10:26 PM   #6
ratmonkey
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The THROTTLE POSITION SENSOR causes both problems. 99% not likely to be your trans or torque converter.
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Unread 05-25-2011, 11:24 AM   #7
stmprnch
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Switch Replacement

Quote:
Originally Posted by jr4x4 View Post
replace the brake swich under brake pedel. my jeep was doing same thing at 55 & over almost felt like slipping. 2 tranny shops told me my tranny was going. 10 bucks & problem fix'd. & if your o/d isnt working it's usally that swich too.
OK, so I check the switch and it tests bad with my meter. Replace the bad switch and still have one of the symptoms, the low idle at a slow rolling slow down. I'm thinking that I also need to go after the O.D.S. that Tally has mentioned.

More to come.

Ron
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Unread 05-25-2011, 11:30 AM   #8
stmprnch
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Write up location?

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Originally Posted by TallyZJ View Post
Yes. There is a good writeup in the drivetrain section or look in the FAQ
I guess it's my day to be blind, I can't seem to find a write up for replacing the O.D.S.

Can you post a link?

Thanks

Ron
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Unread 05-25-2011, 05:38 PM   #9
TallyZJ
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Right here:

http://www.jeepforum.com/forum/f310/...te-up-1182260/
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Unread 05-25-2011, 09:57 PM   #10
stmprnch
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T.P.S. Tst Results

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Originally Posted by ratmonkey View Post
The THROTTLE POSITION SENSOR causes both problems. 99% not likely to be your trans or torque converter.
The T.P.S. tests good and the I.A.C. is new.

Is there history of T.P.S. intermittent problems? I've tested it a number of times, cold, warm, wet days, dry days, with and without Budweiser.
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Unread 05-25-2011, 10:04 PM   #11
ratmonkey
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How did you test it? an analog meter is best for this sensor
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Unread 05-25-2011, 10:18 PM   #12
stmprnch
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Common Tranny?

Quote:
Originally Posted by TallyZJ View Post
That write up is by Fireman33, who owns a 2003 WJ and writes about the 42RE tranny.

It's been a while since I was inside my '93 ZJ with the AW-4 tranny but they look to me like their is noticable differences and similarities. Should the take away be that if you can open the garage door that this is a doable service task? I'm a descent shade tree wrench so I don't mind doing the work, but I do want to do the work that solves the problem.

Thanks

Ron
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Unread 05-26-2011, 07:44 AM   #13
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Testing Testing

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How did you test it? an analog meter is best for this sensor
All previous tests were done with the D.V.M. so I pulled the old analog out of the tool box. It's been a while since this one has seen much sun light.

My readings are nominally the same with both meters. The manual that I have describes the test as being above 0.2V at idle and below 4.8V at W.O.T. with the ignition turned on but the engine not running.

My test results are +/- 0.7V and +/- 3.6V.

If the T.P.S. is the problem, and if the problem only shows itself when the engine is running, do I get to a point where I have to throw parts at it to solve the problem? In other words, replace the T.P.S. even though it tests good according to the manual?

Not a very appealing option but the manual is real clear about the engine not runnig during the test so I didn't want to risk creating a problem. Do you know if I can test the sensor with the engine running and not hurt it?

Thanks Rat.

Ron
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Unread 05-26-2011, 01:17 PM   #14
ratmonkey
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you need to run the sensor through full sweep on the tb and watch the whole curve. idle and wot only gives a small portion of the picture for what can be wrong. watch for spikes or valleys in the curve when opening the throttle.
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Unread 05-26-2011, 05:49 PM   #15
stmprnch
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Needle Watch

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you need to run the sensor through full sweep on the tb and watch the whole curve. idle and wot only gives a small portion of the picture for what can be wrong. watch for spikes or valleys in the curve when opening the throttle.
Yup, it's smooth as glass. I re-checked to make sure. Ran the throttle through 6 full sweeps and it is as smooth as the needle moving up and back down.

Now here's a twist that will mess with your head. The MAP sensor was a little flaky so I changed it. We needed to run to town for other reasons so we took the ZJ. It runs like a top. No stumble, no slow ide, no pulsing RPM at cruising speed.

At this point it isn't broken at all. Even though none of the symptoms pointed to the MAP sensor.

So, this problem may be solved. Since it's a daily driver it will get plenty of miles in the next week to either stumble or not.

Thanks Rat.

Ron
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PROTHANE IN CA's & TA's; DAYSTAR URETHANE COIL SPACERS & BUMP STOPS; HOTCHKIS SWAYBARS
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