87 AW4 TC unlocking issue

on my dads 87 XJ, 4.0, AW4, 231, ever since we got it we could tell the torque converter was locking/unlocking fine, no issues. well we recently had to swap brake booster/master cylinders and while hooking the pedal up the torque converter brake switch became out of adjustment, so it wasn't locking at all. so i adjusted it, and now its locking up, but doing so way early and not properly unlocking. in D it will lock up in 3rd and will stay locked up unless you floor it, hit the brakes, or slow down enough. it does not unlock when you let off the throttle either. very annoying to drive. i've tried adjusting the kick down cable, no change. not really sure where to look next. i find it very strange that one day it works fine and the next it doesnt. I should also mention that the fluid is not old and not dirty/burnt.

I don't think there is anything other than the brake light switch connected to the pedal. I just did a wj swap and didn't see anything other than the brake switch. The torque converter shouldn't have a switch that goes to it.

see the clearish white thing on top? thats the TC switch as far as i know. it wasn't until i re-adjusted it when the TC started locking up again. i also have the brake light switch that attaches to the bolt that connects the master cylinder rod with the pedal.

Replace brake switch? Adjust it again? Install a TC lockup switch?
My renix does not lock up on its own, I know that I can replace the switch, but the TC lockup switch works well.

Johnnie Walker said:

Replace brake switch? Adjust it again? Install a TC lockup switch?

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personally, i'd install a switch but its not my XJ, not sure my dad wants to do that. i don't think the switch is at fault though, because it just senses when i hit the brakes so the TC unlocks to prevent stalling the engine. i shouldn't have to tap the brakes every time the TC needs to unlock.

cheapcherokee93 said:

personally, i'd install a switch but its not my XJ, not sure my dad wants to do that. i don't think the switch is at fault though, because it just senses when i hit the brakes so the TC unlocks to prevent stalling the engine. i shouldn't have to tap the brakes every time the TC needs to unlock.

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Not sure if the TCU has any part in this. But, unplug and drive it, see if anything changes?

cheapcherokee93 said:

see the clearish white thing on top? thats the TC switch as far as i know. it wasn't until i re-adjusted it when the TC started locking up again. i also have the brake light switch that attaches to the bolt that connects the master cylinder rod with the pedal.

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That white switch is for the cruise control. It's a double safety to be sure the cruise shuts off when the brake is applied. So, it not only kills the power to the cruise, it dumps the vacuum to the servo.

Do your brake lights work?

2 other things come into play here.

One is the TPS being bad on the "trans side".

The other is that the big connectors for the trans solenoids, TPS, and TCU to communicate are located near the trans dipstick. One is black and the other gray. Unplug them, spray out both sides with electrical contact cleaner and plug them back together. Any resistance in these "information supeerhighway" connectors can cause shifting issues.

Is the 7.5 amp "trans" fuse blown in the fusebox?

I see cruiser54 has beaten me here... most definitely check the TPS, on the RENIX there are two sides to the TPS, so the engine can run fine with no hesitation or throttle response issues while the transmission acts wacky or vice versa.

IIRC one of the connectors he mentions is the NSS connector, the other is for the OSS and trans solenoids. I forget which is which but either one can cause transmission problems, so cleaning both can't hurt at all.

Here's how to check the TPS.

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

I adjusted the TPS per the above procedure on my 88, and it still wasn't locking up. So I put in a lock up swiotch. Works fine now, so my issue has to be in the TCU.

TRCM said:

I adjusted the TPS per the above procedure on my 88, and it still wasn't locking up. So I put in a lock up swiotch. Works fine now, so my issue has to be in the TCU.

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You set the TPS using the square connector?

Or too much resistance in one of the two connectors between the TCU, TPS, and trans solenoids.

That white switch also definitely affects TC lock up.

I did a 96 booster swap and my TC was not locking up because the switch was not adjusted properly. After adjusting it, I now get lock up, though my TC locks up all through third gear too.

Ever change your TCU? 87 did the 3rd gear lockup but not the 88 IIRC. Get a TCU out of an 89 or 90 and you should be fine.

I never did - mine is still the stock 88 TCU as far as I know.

I remember them shifting that way in 87, but didn't remember it for 88. My wife's is an 88 and it doesn't lock in 3rd unless the lever is in 3rd.

cruiser54 said:

I remember them shifting that way in 87, but didn't remember it for 88. My wife's is an 88 and it doesn't lock in 3rd unless the lever is in 3rd.

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I tend to agree with cruiser-- lock up has always been when driving in OD or 3rd and the shifter in 3rd

I'm gonna take her out tonight and see what it will actually do, but I only remember it locking when the shifter is in 3rd. She's an '88 with the original TCU, so I'm assuming it'll do what it's supposed to.....

Shorty said:

I tend to agree with cruiser-- lock up has always been when driving in OD or 3rd and the shifter in 3rd

I'm gonna take her out tonight and see what it will actually do, but I only remember it locking when the shifter is in 3rd. She's an '88 with the original TCU, so I'm assuming it'll do what it's supposed to.....

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Yeah. I'm almost positive it was only in 87 that it locked in 3rd with the lever in OD.

cruiser54 said:

Yeah. I'm almost positive it was only in 87 that it locked in 3rd with the lever in OD.

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it'll be 22:00 Eastern time before I can get an answer, but I'll be taking her down the interstate to get to work today. It's been a while for her-- wish us luck!!:wow:

So then it's a TPS problem.

Does the Snap-On RENIX scanners just tell you what's on the ECU side of things?