Saturday, January 19, 2013

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.

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