Mechanics

SURGING PROBLEM

1995 Jeep Grand Cherokee • 4 cylinder 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
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Dagan
April 22, 2011.



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.

Rasmataz
Apr 22, 2011.
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

Tiny
Dagan
Apr 22, 2011.
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.

Caradiodoc
Apr 22, 2011.
Thank you I will go try it right now because its driving me nuts not knowing.
Jim

Tiny
Dagan
Apr 22, 2011.
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.

Tiny
Dagan
Apr 22, 2011.
What happened to engine speed when you held the brake pedal down?

Caradiodoc
Apr 22, 2011.
It stayed the same. By the way this is a straight 6 not a 4 cyl.

Tiny
Dagan
Apr 22, 2011.
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

Tiny
Dagan
Apr 22, 2011.
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.

Caradiodoc
Apr 22, 2011.
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?

Tiny
Dagan
Apr 22, 2011.
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