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*Updated: 02/06/2022 5:26PM PST

Td27 conversion impasse help request


Figgyboy
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New to the forum and am stalled in a diesel conversion....

I have transplanted a td27 turcpbodiesel from a jdm 1992 nissan caravan into a 1994 hardbody kingcab 4x4. US model, originally V6 automatic.

Engine is in, runs excellent, and vehicle drives.....BUT transmission woes..does not shift, stuck in fail mode.. The diesel tcm has 2 connectors, and 36 pins, while the 94 truck has a single connector with 48? pins. Many many of the wires are different colors between the harnesses

I have the wiring diagram for the US truck TCU, but i have searched the friggin WORLD for a pinout diagram for a 1992 JDM caravan td27 automatic. No luck at all....With both wiring diagrams this would be easy....not so easy given the possible permutations without a guide.

SOOOOOOO.....I need one of three things....

A) A wiring diagram forva 1992 caravan TCU td27 auto

Or...

B) a definitive answer....can an automatic from a 1990-94 4 cylinder (non electronic) be made to work wiyh no tcu or engine connections? I assume a mechanical kickdown for this unit? Yes/no?

Or

C) switch to manual trans, in which case i need a bellhousing and clutch/flywheel for a td27 or td 25. I can easlily source the rest of the parts for this conversion here in Canada., but these items would have to come from abroad....any leads?..

 

Any help/guidance would be gratefully received. Thanks, edward

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I don't think the auto trans has a mechanical kickdown or any provision for one. That said, I've never had one open.

 

How about the wiring where the harness meets the trans? If the Caravan and Hardbody transmissions have similar guts (same number of speeds and control system), you may find it easier to splice the wires where they meet the trans rather than right at the TCU. If you've got enough of the Caravan harness left, you could probably work out the rest of the TCU wiring just by following the wires to where they terminate, then separate it from the donor loom and wire it into the HB.

 

Or you could have a look at the HB TCU to see what it needs but isn't getting (probably tach and throttle position) and scab something together so it can get the info it needs. Of course, given the different torque curves and rev ranges of the two engines, this would probably not perform very well.

 

If that gets you nowhere, there is a rail shifter available for the four-speed that would eliminate your need for a TCU entirely.

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To properly run your td27 with a gas auto trans, you will need to rewire the transmission wiring, as well as use the diesel transmission control unit, it moves the shift points for the diesel engine. I hope you got the diesel torque converter with your swap as well, as it is different than the gas, as well.

 

The wiring for the v6 tcu has the same 2 connector setup, so you could get the connectors from any v6 pathfinder. The wiring pin out is similar to the v6 gas auto trans wiring except there's one or two less wires on the diesel loom and a couple of the sensors go to different places.

 

The gas ecu sends coolant temp, tps etc to the auto trans computer. On the diesel, there's no ecu, so there's engine mounted sensors for the trans. A tps is mounted to the top of the injection pump and the coolant temp is one of three coolant sensors on the upper coolant neck.

 

I could take a picture of the diesel tcu wiring connectors so you have them for wire colour reference, on the weekend. I don't have a diesel wiring diagram, but using the pathy fsm and the Terrano wiring harness I was able to figure it out. I had an entire donor vehicle so I made a custom wiring harness basically 50% pathy and 50% terrano. I'm pretty sure it's just tps and cts, but the rotational sensor on the front of the injection pump might also send a signal there, can't remember that last one. I'll have to check on the weekend.

 

Best I have for now, hope that helps.

Edited by Nefarious
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