knup

Hello - Having a weird issue with my jeep that I could use some help figuring out.

If I put it in Drive it has no power when starting off like it is starting in 4th gear. I can start off in 1-2 then manually shift up and it is fine power wise but occasionally after a short ride it will just feel like it has no power and won't go over about 35mph. If I pull over and turn it off for a minute then start it back up it will run good for a while then repeat the issue. I was thinking the TCU was bad so I swapped in another but no change. I verfied all fuses are good - even the positive in-line to the TCU and it has power at the harness into the TCU. No Check Engine light on...

Thinking of maybe a bad TPS but not sure it could cause this much of an issue.

Any suggestions would be greatly appreciated.

knup

It is a 96 4.0L 4x4 4 door - no motor or drivetrain mods..

K2dark_xj

my 99 did the same thing after sitting along time, it wasn't shifting down at stop signs for some reason. so id shut it off and turn it back on and it'd work till the next stop sign. basically, i did this and it slowly reoccured less often until it just stopped happening.... but maybe im lucky.... or wore through something that will cause a catastrophic failure..... lmao idk. could be a linkage problem or a bad clutch? do you smell burning clutch?

tjwalker

The throttle position sensor absolutely has to be ruled in or out. Yes, it could cause your symptoms. Here is more on it and how to test it. With testing on an intermittent problem though, testing may be inconclusive. May want to get a new one in there.
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The throttle position sensor is connected to the throttle shaft on the throttle body. It sends throttle valve angle information to the PCM. The PCM uses this information to determine how much fuel the engine needs. The TPS is really just a simple potentiometer with one end connected to 5 volts from the PCM and the other to ground. A third wire is connected to the PCM. As you move the accelerator pedal with your foot, the output of the TPS changes. At a closed throttle position, the output of the TPS is low, about a half a volt. As the throttle valve opens, the output increases so that, at wide open throttle, the output voltage should be above 3.9 volts. Testing can be performed with an electrical meter. Analog meter is best. You are looking for a smooth sweep of voltage throughout the entire throttle band. While slowly opening and closing the throttle, take note to the movement of the voltmeter needle. There should be a direct relationship between the needle motion to the motion of the throttle. If at anytime the needle moves abruptly or inconsistently with the movement of the throttle, the TPS is bad

You should have 5 volts going into the TPS. At idle, TPS output voltage must be greater than 200 millivolts. At wide open throttle (WOT), TPS output voltage must be less than 4.8 volts.. The best is to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. With your meter set for volts, put the black probe on a good ground like your negative battery terminal. With the key on, engine not running, test with the red probe of your meter (install a paper clip into the back of the plug of the TPS) to see which wire has the 5 volts. One of the other wires should show .26V (or so). The other wire will be the ground and should show no voltage. Move the throttle and look for smooth meter response up to the 4.49 at WOT.

Perform the test procedure again and wiggle and/or tap on the TPS while you watch the meter. If you notice any flat spots or abrupt changes in the meter readings, replace the TPS.

The TPS is sensitive to heat, moisture and vibration leading to the failure of some units. The sensor is a sealed unit and cannot be repaired only replaced. A TPS may fail gradually leading to a number of symptoms which can include one or more of the following: -

NOTE: The throttle position sensor is also DIRECTLY involved with transmission shifting characteristics! It should be verified early in the troubleshooting process, when a transmission issue is suspected!

• Poor idle control: The TPS is used by the ECU to determine if the throttle is closed and the car should be using the Idle Air Control Valve exclusively for idle control. A fault TPS sensor can confuse the ECU causing the idle to be erratic or "hunting".
• High Idle Speed: The TPS may report faulty values causing the engine idle speed to be increased above normal. This is normally found in conjunction with a slow engine return to idle speed symptom.
• Slow engine return to idle: A failing TPS can report the minimum throttle position values incorrectly which can stop the engine entering idle mode when the throttle is closed. Normally when the throttle is closed the engine fuel injectors will be deactivated until a defined engine RPM speed is reached and the engine brought smoothly to idle speed. When failing a TPS will not report the throttle closed and fueling will continue causing the engine to return to idle very slowly.
• Engine Hesitation on Throttle Application: The TPS is also used by the ECU to determine if the driver has applied the throttle quicker than the Manifold Air Pressure sensor can read. The fueling is adjusted acordingly to cope with the sudden increase in air volume, however a faulty sensor can cause the ECU to ignore this data and the engine will "hesitate" when applying the throttle. In extreme cases with the engine at idle, a sudden application of full throttle can stall the engine.
• Engine Misfire: A fault TPS can report values outside the deined acceptable range causing the ECU to incorrectly fuel the engine. This is noticable as a slight misfire and can trigger the misfire detection software and/or Malfunction Indicator Lamp (MIL) light on the dashboard. Extreme cases can cause excessing misfires resulting in one or more cylinders being shut down to prevent engine and catalytic converter damage.

knup

Ok - Checked the TPS and it was reading good. Threw a new one in just to be safe but didn't fix the problem of it wanting to start off in 4th.

Any other ideas of what I should be checking for?

Anyone around Fredericksburg, VA that would be willing to take a look and offer an opinion?

knup

Ok - checked and cleaned all of the connections under the hood with electronic spray and all are good but no changes. Swapped in another TCU an no difference at all. It's weird but it acts the same whether the TCU is connected or not - I can shift manually but it won't shift at all on its own. Still no check engine light and no codes stored - I know the light is good because it came on when I changed the TPS but cleared after I drove it a bit. Guess I will move on to checking the shift solenoids.

knup

Found both shift solenoids were bad but the lock up was good. Went ahead and changed all three out and now it is shifting good. Haven't had a chance for a far enough trip to see if it will still have the loss of power issue but think it was tranny fluid getting overheated that was causing it. I plan on taking it to a friends shop tomorrow that it didn't make it to without having to pull over a couple times last week.