Xj.guy

Have own my second xj for about three months and two weeks ago I realized I had another gear? It's an automatic. Before at 55 the RPMs were 2300 now there at about 1700. I know it's another gear but why did it only recently shift up?

notop46

Have you done anything different to it in the 3 months (maint, repairs, driving habits)? If not, then you have a self-healing Jeep.

Donnie_K

lol, did it sit for awhile?

The Blacksmith

Christine

Xj.guy

No change other than the weather? I guess OD works but when ever it wants too? It kind of has a mind of it's own?

kjc

You might check out/adjust your brake switch. On my '93 Laredo it's a multi-function switch. It works the brake lights, but it's also wired in to the overdrive circuit. When you're in OD, keep steady on the gas and touch lightly on the brake pedal. See if it drops out of overdrive. It also kills the cruise control if you have it. Just a guess

Xj.guy

I tested it and when it's in OD if I push the brake pedal it drops out. How do I go about adjusting it? Or how do I fix this

kjc

Well, that sounds normal.. it should drop out of overdrive when the brake pedal is pushed. If your rpms are lower now, then i'd guess it wasn't shifting to OD before. So... it seems to be ok now? I mean you want it in OD on the highway
So, to clarify, at first it was @2300 rpm (maybe not in OD for some reason) and now it has dropped to @1700 (now shifting in to OD?) Sounds like it fixed itself.

cruiser54

A funky TPS could be the cause, too.

Xj.guy

Yes I believe before I wasn't shifting into OD but now again it seem to have a problem. It's been four days now and no OD? Does any one know possible fixes? Maybe regearing? I don't know to much about how OD works?

Xj.guy

What is a TPS? Thanks

cruiser54

Throttle Position Sensor.

It's located on the throttle body and has 2 harnesses connected to it. One sends info to the ECU (Engine computer) and the other send info to the TCU (Transmission Control Unit). If the TCU is thinking the throttle is in a different position than it actually is because of a faulty TPS, you could have OD issues.
Got a voltmeter? It's easy to check using the following wirte-up.

RENIX TPS ADJUSTMENT
Before attempting to adjust your TPS be sure the throttle body has been recently cleaned.
It's especially important that the edges of the throttle butterfly are free of any carbon build-up.
IMPORTANT NOTE: Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector
of the TPS . The letters are embossed on the connector itself.
Touch the black lead of your meter to the negative battery post.
If you see more than 1 ohm of resistance some modifications to the sensor ground harness will be
necessary. The harness repair must be performed before proceeding.
I can provide an instruction sheet for that if needed.
MANUAL TRANSMISSION:
RENIX manual transmission equipped XJs have a three-wire TPS mounted on the throttle body.
This manual transmission vehicle TPS provides data input to the ECU. The manual transmission
TPS has three wires in the connector and they're clearly embossed with the letters A,B, and C.
Wire "A" is positive.
Wire "B" is ground.
Key ON, measure voltage from "A" positive to "B" ground by back-probing the connectors..
Note the voltage reading--this is your REFERENCE voltage.
Key ON, back-probe the connector at wires "B" and "C". Measure the voltage. This is your
OUTPUT voltage.
Your OUTPUT voltage needs to be seventeen percent of your REFERENCE voltage. For
example: 4.82 volts X .17=.82 volts. Adjust the TPS until you have achieved this percentage. If
you can't achieve the correct output voltage replace the TPS and start over.
AUTOMATIC TRANSMISSION:
RENIX automatic transmission equipped XJs have a TPS with two connectors. There is a flat three-
wire connector, same as the manual transmission vehicles have, and it is tested the same as the
manual transmission equipped vehicles--FOR ENGINE MANAGEMENT RELATED ISSUES.
However, the automatic TPS also has a square four-wire connector clearly embossed with the letters
A,B,C, and D. It only uses three wires and provides information to the Transmission Control Module.
Key ON, measure voltage between "A" positive and "D" ground. Note the voltage. This is your
REFERENCE voltage.
Back-probe the connector at wires "B" and "D". Measure the voltage. This is your OUTPUT
voltage. Your OUTPUT voltage needs to be eighty-three percent of your REFERENCE voltage.
For example 4.8 volts X .83=3.98 volts. Adjust the TPS until you have achieved this percentage.
If you can't, replace the TPS and start over.
So, if you have an automatic equipped XJ your TPS has two sides--one side feeds the ECU, and
the other side feeds the TCU. If you have TRANSMISSION issues check the four-wire
connector side of the TPS. If you have ENGINE issues check the three-wire connector side of
the TPS.
For those with a MANUAL TRANSMISSION--the TPS for the manual transmission XJs is
stupid expensive. You can substitute the automatic transmission TPS which is reasonably priced.
Revised 11-28-2001