Tranny wont slip into overdrive?
 

Does first second and third fine, but when I get around thirty five or forty mph it's like she can't find overdrive... I was maybe thinking it could be the shift selenoid? It's the DD so I'm at a loss if it's the tranny I need an escape and I'm hoping that it's the selenoid :/ any ideas ladies/gents?

Mine did the same thing, ended up being my NSS, took it out and cleaned it. Good as new

Forgive me for being mechanically inclined lol but what's NSS?

Neutral safety switch

Ahh thank you!

My zj was doing the same thing, and it turned out to be a sensor that was located just under the drivers side, I wanna say it was called transmission speed sensor? Uhg! Anyhow, it was leaking and shorting out causing my problem, and after alot of money and needless replaced parts by a "repitable" company, a simple lil replacement of a sensor was all it was! Gggrrrr!

What year is it?

check your throttle postion sensor, that helps it go into overdrive too. mine wouldnt go in either until i found out it was bad and changed it. i was doing 60- 65 all that time in third gear i believe, and sucking the gas down way too fast.

It's an 88' , and thAnk you guys so much I will check and replace all of these sensors and switches if I have to before I think about havin to rebuild the tranny. This gives me hope! Lol

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: Set your meter to measure Ohms. 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. Wiggle the wiring harness where it runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too.
If you see more than 1 ohm of resistance, and/or fluctuating 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 03-13-2012