AW4 TC No Lockup

Here's one for the AW4 experts.

Noticed recently that my 90XJ (189K) no longer engages the TC lockup either in Drive or No 3 GearShift position. Also I noticed no change in shift points while engaging the power/comfort switch. The transmission shifts smoothly and at the correct RPMs as far as I can tell (except for the TC lockup). This has reduced my gas mileage to about 15MPG so I'm trying to correct. Things I've checked at the TCU computer are:

Verified pulses at C3 input while vehicle is moving (approx 6VDC on/off).
Verified power/comfort switch voltage input at TCU connector with switch on.
Verified continuity at TCU connector for solenoids 1 thru 3 (approx 12 ohms).
Verified voltage at TCU connector for brake pedal input (only present with brake depressed).
Verified continuity at TCU connector back to TPS inputs.
Verified TPS resistance range/changes while manually moving throttle to full open (engine off)
Verified TCU inputs fron Neutral Safety Switch (NSS recently removed and cleaned)
Verified TCU connector fused battery voltage inputs (including ignition switch)

Connecting a voltmeter to the solenoid 3 output at the TCU connector reveals 0VDC with car at 50mph and in Drive position. I didn't check solenoids 1 and 2 since the transmission shifts fine otherwise. Jumpering battery voltage to the terminal will engage the TC lockup.

Transmission fluid is red in color and at full mark with vehicle hot.

Vehicle has ABS brakes but didn't see any overlap with TCU.

Could the TCU be bad?? The question is why won't the TCU do it and why doesn't the power/comfort switch appear to have any effect?

Will a TCU from a 1994XJ work (MPI to Renix)? I have a spare but didn't want to plug and play without research.

Backup lights work? check the fuse marked TRANS. and the break light switch.Never mind you have those voltages.
You do not get TC lockup untill the engine is warmed up, so a bad temp sensor could cause bad mileage and no lockup.

I have this very same problem with my 90. I ended up wiring an independent switch for the TC and manual 2nd. I noticed that there's a speedo switch (2 wire) inline with the odometer cable adjacent to the firewall. I'm unable to locate any reference to this sensor from the dealer or online (not having any Renix Lit. handy sux) so I can only take a guess that this crude VSS may possibly be the culprit.

I think thats the service minder switch.

Backup lamps work. This is one of the reasons the NSS switch was removed and cleaned. The 1/2 and the 3 position indication from the NSS were verified at the TCU connector pins and per the gear shift lever. Everything seems fine since the 1st and 2nd gears are shifting normally. The brake lamp holdown circuit was verified twice. There is normally 0V at the TCU connector until you depress the brake pedal. This opens the circuit and allows 12V to be present at the TCU input. There are actually 2 switches at the brake pedal. Both were verified visually and confirmed with a voltmeter to be functioning properly.

I am curious about the warmup though. I do not see any electrical interconnection between the transmission TCU and the engine temp sensor which inputs into the RENIX ECU per the factory service manual.. The only input into the transmission TCU appears to be from the throttle body TPS circuit. This appears to be functioning properly and electrical connections to the TCU were verifed through ohmeter checks.

is there actualy a reader computer that can hook up to the 1990 jeep?
i did not know this

90xj06 said:

is there actualy a reader computer that can hook up to the 1990 jeep?
i did not know this

Click to expand...

Yes the Snap On MT2500 will pull realtime data from the renix ecu and the AW4 TCU

pps said:

Backup lamps work. This is one of the reasons the NSS switch was removed and cleaned. The 1/2 and the 3 position indication from the NSS were verified at the TCU connector pins and per the gear shift lever. Everything seems fine since the 1st and 2nd gears are shifting normally. The brake lamp holdown circuit was verified twice. There is normally 0V at the TCU connector until you depress the brake pedal. This opens the circuit and allows 12V to be present at the TCU input. There are actually 2 switches at the brake pedal. Both were verified visually and confirmed with a voltmeter to be functioning properly.

I am curious about the warmup though. I do not see any electrical interconnection between the transmission TCU and the engine temp sensor which inputs into the RENIX ECU per the factory service manual.. The only input into the transmission TCU appears to be from the throttle body TPS circuit. This appears to be functioning properly and electrical connections to the TCU were verifed through ohmeter checks.

Click to expand...

I'm still looking but the ECU's are different for the auto for a reason, it could be they share data or the manual shift light.

There is also one input on the TCU (D2) that says from ecu power in pin 22?

Ok all the ECU would need to do is send 5 vdc to (D2) on the TCU that would unlock the converter the same as WOT.

You won't believe this! Torque converter lockup began working in the middle of my fiddling with the TCU. Upon rehooking up a DVM to Solenoid 3 output at the TCU and test driving the vehicle, the TC lockup started to work normally and was confirmed by DVM voltage reading. The only thing that's funny now is that when you leave off the gas the TC comes out of lockup and as soon as you depress the accelerator again, the TC goes back into lockup. Is this designed to operate this way or should the TC remain in lockup irregardless? If it isn't, the TPS may be on the edge of acceptable calibration?

pps said:

The only thing that's funny now is that when you leave off the gas the TC comes out of lockup and as soon as you depress the accelerator again, the TC goes back into lockup. Is this designed to operate this way or should the TC remain in lockup irregardless?

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That's the way it is supposed to work. The TC will unlock when you decelerate, especially when RPMs are close to the TCs stall speed.

Dave

As you know it's a duel TPS but the trans section can't be adjusted separately from the engine section. The Trans section must have a dead spot in it,

I think I have the same problem so if you could check out this post that I put up I would appreciate it greatly,Thanks in Advance

Tranny problem??

pps said:

I am curious about the warmup though. I do not see any electrical interconnection between the transmission TCU and the engine temp sensor which inputs into the RENIX ECU per the factory service manual.. The only input into the transmission TCU appears to be from the throttle body TPS circuit. This appears to be functioning properly and electrical connections to the TCU were verifed through ohmeter checks.

Click to expand...

Correct, on the Renix there are no connections between the engine computer and trans computer.

pps said:

Will a TCU from a 1994XJ work (MPI to Renix)? I have a spare but didn't want to plug and play without research.

Click to expand...

Starting with the HO and ODBI setup, there is a odb diagnostic communcation connection and a TPS connection between the engine computer and the TCU. On the renix, those pins are wired to the diagnostic connector under the hood.

The ODBI and ODBII engine computer provide the TPS signal instead of using a seperate set of outputs on the TPS. Same pins, and I believe (but have not verified) that the voltages are the same as the Renix TPS provided. The HO manual ecm doesn't has the tps output, which is an issue for folks doing a manual -> auto swap.

I have compared the pinouts and connectors between a 93 and 88 TCU (since sold them on eBay). I believe you can use the 94 TCU, but you will have to remove the plastic keying ridge on the outside of the connector to get them to slide together. The connectors are identical except the color and the location of the ridge.