Jeep Wrangler Erratic Shifting

1999 Jeep Wrangler Under Full Throttle Jeep Shifts At 4k RPM

Throttle Shifts In and Out of Overdrive.

It can be issue with TPS also called as Throttle Position Sensor.


As per our Auto garage repair Experience I will share few troubleshooting tips regarding the cause and solution to this problem


As per what you mentioned I  expect more than 4,000 RPM at wide open throttle but not much more than that.

We at our Auto garage have noticed many such problems it's very much possible that low engine power is the issue. 
Another possibility is Low fuel pressure.
Low fuel pressure could cause it but that would usually come with spark knock on acceleration. 
But as you mentioned low engine power and erratic shifting with no error codes retrieved the most common cause of lack of engine power with no codes is a restricted catalytic converter due to internal breakup. 
To confirm the problem.
A backpressure test can be done to check the converters.


There are many other possibilities that can too cause these issues:-------
Like transmission related:-----
There are a couple things transmission related that could cause it too. 
As per your jeep brand and model/ year mentioned , it has primitive three speed trans with a mechanical governor in the tail housing. As per what i recollect these governors gave some trouble over the years with the governor valve sticking in the bore and causing shift issues.May be what exactly you are noticing, called low engine power and erratic shifting. It's very possible that the governor is stuck. To confirm whether governor pressure is issue.Governor pressure can be checked with a pressure gauge on the governor pressure tap on the trans.

As earlier mentioned it can be faulty throttle position sensor, but also It's possible that the throttle valve cable could be misadjusted too. 
To understand throttle cable working read the following:-----
The throttle valve cable goes from the trans to the throttle body.Now when you open the throttle it moves the throttle valve in the valve body and this has a huge influence on shift timing. If the cable was adjusted too long it would cause upshifts to be early.And may be these is what your problem.

As per your problem mentioned there is no one confirm solution to be pinpointed but there are few possibilities.Each can be possible.So looking at all possible issues will help you know what caused these issue on your jeep wrangler.


Like its mentioned before the erratic shifting is a common symptom of a governor issue or misadjusted throttle valve cable so those two things are where you're going to need to start. 

Like other possibilities, it can  be a leaking front clutch too, but definitely start by addressing these other things.

For  overdrive issue which you mentioned is actually torque converter lockup, it's a three speed transmission. Since you're having erratic idle and torque converter clutch operation at the same time it's extremely likely that the throttle position sensor issue. 
I suggest get the TPS inspected and replaced and see if same problem is there or its gone.
If you need to confirm the issue with TPS before getting New TPS, you can try these simple TPS test procedure.When it's idling erratic you can unplug the sensor, if the idle calms down then you know the TPS is the problem. 

At out garage we have also seen in some cases that problem was actually not TPS but it was  with TPS connector terminal grip, replacing the connector may take care of  problems. If you do replace the TPS  be sure to use a Mopar sensor to avoid future problems.It a good reputed brand of parts.


These details will help.
Thanks.

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How to test TPS sensor?

Unplug the TPS electrical connector. Turn on the ignition switch, but do not start the engine. Using a voltmeter, probe the connector’s terminals coming from the computer side to test for supply voltage. Touch the negative lead to the connector’s terminal ground--most likely the black wire--and the meter’s positive or red lead to the connector’s terminal reference voltage wire, a blue or gray color wire. Your meter should read a steady 5.0 volts at the terminal. If you don’t receive this voltage reading, there is an open or short in the supply wire. Turn off the ignition switch and plug the electrical connector back to the TPS.

Test the TPS for signal voltage to the computer. Insert a pin through the ground wire and another pin through the signal voltage wire and connect the voltmeter probes to the pins using alligator clips. Start the engine. As you manually open and close the throttle plate, watch the voltage readings at the meter. The voltage should gradually increase from 1 to 5 volts and back to 1 volt. If you see erratic movement or no movement of voltage signal, replace the TPS. Turn off the engine.

Test the TPS’ resistance. This is an alternate method to test a TPS equipped with a variable resistor. Unplug the TPS electrical connection. Set your multimeter to ohms. Connect the ohmmeter probes to the sensor’s supply and signal wire contacts. Manually open and close the throttle plate and watch the resistance reading at the meter. The resistance should gradually increase and decrease as you open and close the throttle plate. If there is an erratic resistance change, no change, or no resistance at all, replace the TPS.

But TPS sensor if checked good then the possibility for car not advancing on the acceleration

is low fuel pressure, timing problem, or worn out distributor.--------

In your case timing and fuel pressure checked ok, so the distributor needs to be replaced.----------

a lean condition could be a 02 sensor or low fuel pressure.

you want to see 38-46 psi under full load and 28-36 at idle.

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For car error code diagnosis click the link below:---

http://www.automd.com/diagnose/?amdcid=apwldrbrd1

Car no start:--

http://technoanswers.blogspot.com/2011/05/car-will-turn-over-but-will-not-start.html