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Renix AW-4 Transmission Swap into a YJ
'87 XJ AW-4 into '93 YJ
By Shad Ahlstrom


I used a very small flat blade screwdriver to rotate the torque converter through the bolt holes in the flexplate until the threads lined up.  I twisted one bolt in there finger tight.  I used a larger flat bladed screwdriver to rotate the flexplate tooth by tooth until I got all 4 bolts in finger tight.  I torqued them down using the screwdriver to resist rotating the whole flexplate.  The transmission cooler plumbing was a pretty close match between the XJ and the YJ.  I had recently replaced the radiator and Radiator Barn was nice enough to add hose nipples to the bottom of the radiator for me.  The output line had a quick connect fitting right near the passenger side fitting.  I used the short quick connect end to go straight into the radiator.  I had a B&M Supercooler to install so I didn't need any of that
quick connect stuff for the other end.  I mounted the Supercooler in front of the AC condenser right behind the grill using the metal straps in the B&M kit.  I plumbed the hose out of the radiator and into the bottom of the Supercooler.  From the top of the Supercooler, I ran a hose to a barbed splice in the factory rubber hose.  From there, it returns to the transmission.  I needed to create a hanger from the oil pan to hold the lines tight.

I bolted the skid plate back on and bolted the trans mount to the skid plate.  I cut the exhaust hanger off the pipe and installed it.  I then took care of the rest of the wiring, minus the park/neutral switch and the reverse lights.

This TCU requires a reversed signal from the throttle position sensor.  What I mean is, the engine's TPS is a 5v system.  At idle, the engine's TPS sends out 0V and gradually sweeps up to +5V at full throttle.  This particular transmission control unit ('87-'90) has a reverse sweep.  +5V at idle and drops as the throttle is opened.  I attempted to build a voltage reverser with various resistors, condensers and a 555 timer but all I could come up with was a logic circuit.  +5 volts or 0 volts with no sweep.  I gave up after a few hours of playing with this.  If anybody knows how to do this properly, I'd love to know.

I bought a GM style TPS from the local auto parts store.  It's from a 3.8L V6.  I chose this one because it's cheap, adjustable and comes with an arm as opposed to a socket. 

I bent some steel to form a bracket that bolted to the throttle body and added some ball chain to connect the two.



The sweep from the throttle linkage was a little greater than the sweep from the TPS so I needed to build a little bracket to prevent the ball chain from snapping at wide open throttle.  After a little tweaking, I was able to get +5.1V at idle and +1.8V at wide open throttle.  It's not 0V but it will do for now.  I'll come up with a better system later on.  I added about 1.5 quarts of transmission fluid to the transfer case and 6 more quarts to the transmission (8 total).  Then I went back over every single bolt I touched to make sure I torqued everything.  I set the TV cable by pressing in the button, twisting the throttle to wide open and releasing the button.  This is supposed to set it automatically.  I put the negative cable back on the battery and turned the ignition to ON.  I looked over everything and it all seemed to be OK.  No fuses blown, TCU is staying cool.  Time to go for it!  I turned the key to start.  It cranked but no start.  It's acting more like an XJ already...


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