Surging problem

Tiny
DAGAN
  • MEMBER
  • 1995 JEEP GRAND CHEROKEE
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 120,000 MILES
HAVE A 1995 GRAND CHEROKEE LARADO THE TAC SURGES BUT I GAIN NO SPEED, THE TAC WILL SURGE UP THEN DOWN THEN UP AND DOWN THEN IT SOUNDS LIKE IT IS GOING INTO PASSING GEAR BUT I GAIN NO SPEED. THEN THE TAC WILL DROP TO NORMAL AND START ALL OVER AGAIN. IDEL IS GOOD IDLE WITH A LOAD ON FOOT ON BRAKE IS GOOD. IT IS JUST GOING DOWN THE ROAD IT WILL DO THIS AND IT IS CONSTENT
Friday, April 22nd, 2011 AT 7:18 PM

16 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Could be caused by one of the following below

Oxygen sensor.
Catalytic converter.
Fuel injectors dirty/sticking.
Mass airflow sensor/Airflow meter.
Throttle position sensor.
Crankshaft position sensor
Knock sensor
Manifold absolute pressure sensor.
EGR Valve
Fuel pressure regulator leaking or defective fuel pump.
Fuel contamination.
Foul/defective spark plugs.
Open spark plug wires.
Ignition coil/Coil packs defective.
Incorrect ignition timing.
Cap and rotor.

Note:If it doesn't apply disregard it and keep testing.
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Friday, April 22nd, 2011 AT 7:23 PM
Tiny
DAGAN
  • MEMBER
  • 10 POSTS
I changed the tps sensor and the speed sensor on the trans. Still is doing it. If I have it scoped will it find the problem? I am getting no codes on this. I also had the tras scanned and it was ok
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Friday, April 22nd, 2011 AT 7:39 PM
Tiny
CARADIODOC
  • MECHANIC
  • 34,086 POSTS
Sounds like the lock-up torque converter is kicking out. The clue is engine speed will go up by 200 rpm when you are in third or fourth gear and above about 45 mph. Try holding the brake pedal up with your foot. If the problem stops, readjust the brake light switch.

If it still acts up, try driving at a steady highway speed and hold the brake pedal down just a little. If the engine speed stays higher, replace the brake light switch.
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Friday, April 22nd, 2011 AT 8:04 PM
Tiny
DAGAN
  • MEMBER
  • 10 POSTS
Thank you I will go try it right now because its driving me nuts not knowing.
Jim
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Friday, April 22nd, 2011 AT 8:28 PM
Tiny
DAGAN
  • MEMBER
  • 10 POSTS
Ok just got back at first it didnt do it as I held the brake pedal up I was going 40 to 45 mph. As I fot up to 50mph it started doing it. I pressed on the brake pedal at 50mph a little and held the 50mph.
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Friday, April 22nd, 2011 AT 8:48 PM
Tiny
CARADIODOC
  • MECHANIC
  • 34,086 POSTS
What happened to engine speed when you held the brake pedal down?
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Friday, April 22nd, 2011 AT 8:57 PM
Tiny
DAGAN
  • MEMBER
  • 10 POSTS
It stayed the same. By the way this is a straight 6 not a 4 cyl.
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Friday, April 22nd, 2011 AT 9:00 PM
Tiny
DAGAN
  • MEMBER
  • 10 POSTS
It is weird it only does this when I am going down the road. Sitting still in park great idel no miss the tac stays steady. With a load on it my foot on the brake its is good stays steady no miss tac stays steady also. It is just going down the road.
Jim
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Friday, April 22nd, 2011 AT 9:04 PM
Tiny
CARADIODOC
  • MECHANIC
  • 34,086 POSTS
Tapping, (or holding) the brake pedal gives the signal for the computer to unlock the torque converter in preparation for coming to a stop. It would seem that undesired unlocking is what you're feeling. Now the question is why is it unlocking while you're driving. An intermittent brake light switch is one possible reason. A bad spot on the throttle position sensor is another but you replaced that already. There could be a wiring problem to the TPS too but that should set a fault code and turn on the Check Engine light.

If holding the brake pedal up doesn't help, the next thing would be to connect a scanner that can display live sensor data while you're driving. Many of them have a record function that lets you slowly review the data when the problem occurred. When the problem acts up, you press the "record" button. Because the data passes through the scanner's memory, the recording actually begins a few seconds before you pressed the button.

When you play the recording back you can look at what changed just before the torque converter was commanded to unlock. If the command to remain locked up never turned off, it is not a sensor or switch problem; it is a problem within the transmission itself. That would not be very common.
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Friday, April 22nd, 2011 AT 9:15 PM
Tiny
DAGAN
  • MEMBER
  • 10 POSTS
I had the transmission scanned while the tech was driving it and it showed nothing. He told me he would need it in the shop to go over it. If I have this scoped will it help pin point the problem or am I just wasting my money?
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Friday, April 22nd, 2011 AT 9:25 PM
Tiny
CARADIODOC
  • MECHANIC
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I would have it test driven by someone from a transmission specialty shop first to verify it's really the torque converter unlocking. If it is, you can be fairly certain they've seen it before or at least will know what to look for.
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Friday, April 22nd, 2011 AT 9:47 PM
Tiny
DAGAN
  • MEMBER
  • 10 POSTS
Thank you I am going to put it in the shop on Monday and see just what is going on.I will let you know what they find.
Jim
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Friday, April 22nd, 2011 AT 10:05 PM
Tiny
DAGAN
  • MEMBER
  • 10 POSTS
Hey cardiodoc tok the jeep to a local transmission shop with a good reputation. They said that one tech drove my jeep the other run the scanner and it come back as a bad output speed sensor on the trans. I told them that I had replaced that sensor and he said that he seen the one I was talking about and this was a differnt one something about having to remove a crossmember to get at. 150.00 to put in he told me. Does this sound right to you as to this sensor being the problem
Jim
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Monday, April 25th, 2011 AT 8:42 PM
Tiny
CARADIODOC
  • MECHANIC
  • 34,086 POSTS
I'm not a Jeep guy so I can't speak to the cross member issue, but from my Chrysler experience I have no reason to doubt the diagnosis. I DO know these sensors cost more than I remember from the '90s so with the labor to remove a cross member it sounds like they are being fair.
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Tuesday, April 26th, 2011 AT 12:33 AM
Tiny
DAGAN
  • MEMBER
  • 10 POSTS
Well I told them to go ahead an do it they are the experts, they called last night around 5 told me the jeep was done and I could pick it up.
That was it my jeep is back to normal again. 174.00 I feel was more than fair to get this problem solved. Well that and the other cost I pit out for the new tps sensor and the other speed sensor on the trans.
Thank you for all your help you were the only person I could find on this computer who cared enough to talk to me
Many Thank's
Jim
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Tuesday, April 26th, 2011 AT 8:17 AM
Tiny
CARADIODOC
  • MECHANIC
  • 34,086 POSTS
All right. One in a row! Happy to hear you can buzz off, ... Ah, ... I mean SAIL off into the sunset.
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Tuesday, April 26th, 2011 AT 9:43 PM

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