Guntar13

I have a 89 sport 4.0, with Auto Trans. The fluid level is fine, recently did a drain and fill, and no matter at what temperature the thing shifts kind of funny. It will shift at all the right points no problems; nice and smooth. I notice though when it gets into overdrive just the slightest lift of the pedal and it will down shift. Going through town this is pretty annoying since it is constantly downshifting and up shifting. Just wondered about some insight from everyone. thanks.

tjwalker

The "throttle position sensor" is directly involved with automatic transmission shifting performance. It is a primary suspect here.

Job #1 is for you to test and adjust it....the tps on the 87-90 is adjustable. Here is more courtesy of Cruiser54.
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RENIX (87-90) 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 one 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 other 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 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 four-wire connector clearly embossed with the letters
A,B,C, and D.. For the automatic transmission equipped vehicles the four-wire connector
provides data to the TCU.

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.

Guntar13

WOW! I think my brain just went somewhat the consistency of scrambled eggs! Just kidding thanks for the very good info. I didn't realize that sensor also controlled or gave signal to the transmission, definately will do some checking later. Thanks again.

cruiser54

You also have a Power/Comfort switch on the dash to the right of the steering column. What setting is it in and is the light on in the switch?

Guntar13

I do know that switch, I drive around in comfort all the time, I have verified that it is working also. Thanks

cruiser54

So it lights up when put in the Power mode?

Guntar13

yeah for sure, it lights up and the shift pattern noticeably changes when it is in that mode, (drove home from work that way and it didn't seem to be having the original problem, but it appears that for distance or normal driving it would kill the gas mileage. thank you

cruiser54

It does not kill mileage and makes the trans shift acceptably, probably eliminating the issue you're complaining about. So much so, that the factory eliminated the Comfort setting and defaulted to the Power setting when they eliminated that switch.

blinkbears

I just had this problem literally 5 days ago with my 88 XJ and I assure you with 1000% certainty that your TPS is bad. I replaced my old one, adjusted the new one with my voltmeter, now the darn thing shifts good as new.

REPLACE THE TPS! DON'T WAIT!

blinkbears

Guntar, you better replace your TPS and then get back here to tell us about how awesome your XJ is shifting.

I'll be waiting....

cruiser54

That describes the Comfort/Grandma mode to a "T". Try the Power mode for a few days.

Guntar13

I agree with cruisers post, it certainly makes it shift a ton better but I feel like that is a band aid fix for the underlying issue? I definately was going to check out the tps and adjust/replace As needed ( just gotta get some garage time) . Probably just take the whole throttle body out and give it a good cleaning while I'm at it! I will report back with the results!

cruiser54

I agree you should test the TPS. Make sure you do it on the trans side!! Try the Power mode though. When I was Service Manager and Shop Foreman back at the dealership when these were new, we solved 90% of trans complaints by convincing "economy minded" people to leave the switch in Power. If leaving the switch in Power mode hurt fuel mileage, the factory never would have eliminated the switch and defaulted the TCU to Power, would they?

Guntar13

point well taken sir!