1HD-FTE Engine Swap - Will A750F Engine ECU Communicate with A442F TCU?

[254cruiser]

Good day legends

Long time lurker, first time posting on this one because I've hit a specific question I can't find a definitive answer to and I know this community has forgotten more about LC100s than most people ever learn.

I'm doing a 1HD-FTE engine swap between two HDJ100s. The donor car is a later 5-speed automatic (A750F) and the recipient is an earlier 4-speed automatic (A442F). Both are LC100 chassis, both 1HD-FTE, so mechanically it's straightforward — same mounts, same bellhousing family.

The donor engine is coming with its matched ECU and injection pump as a pair, which I understand is the right way to go for pump/ECU calibration reasons.

My specific question is around ECU-to-TCU communication:

Will the A750F-paired engine ECU communicate correctly with the A442F TCU — specifically the torque reduction handshake during shifts? I understand these are relatively simple discrete signals rather than CAN bus, but I'm conscious that the signal format, voltage, or pinout expectations may differ between what the A750F TCU sends and what the A442F TCU sends on that line.

Has anyone done this combination, or does anyone have the pinout data to compare the two? Trying to establish whether I'm looking at a clean swap, harsh shifts, or potential fault codes before the engine goes in.

Appreciate any knowledge you can throw at this.

 

[sjpitts]

I don't know the answer to your question -- but I will say that here in the USA people are starting to pay significant money to replace 442F transmissions with the more modern A750F. There seems to be lots of benefits to the later five speed. At least enough to justify the cost of the swap.

 

[254cruiser]

I don't know the answer to your question -- but I will say that here in the USA people are starting to pay significant money to replace 442F transmissions with the more modern A750F. There seems to be lots of benefits to the later five speed. At least enough to justify the cost of the swap.

Unfortunately here in Kenya I have to work with what I’ve got or can get , if I had the later box and ECU I would change them both but unfortunately I don’t I’ve only got the engine .

 

[uHu]

The hdj100 with the A750 has a combined ECU for engine and transmission, and it works a bit differently, and much snappier, than the two ECUs in the A442 version. There are also differences in the control of the IP, as the newer engine has mechanical differences as well. (Injectors, valves, butterfly valves, turbo, IP control characteristics, etc).

Back in 2009, I put an engine and A442 from a 2000 into a 2004. As it was a temporary swap for only a week (long story, but for tax reasons) I didn't look very carefully into the signalling and control of the gearbox. But, what I did do, was asking around on the LCOOL forum based in Australia, as this kind of operations are more common there. (That forum has been down for a few years now). What I found was that the engine will run well enough (with a sensor or two missing), but that there is no way to get the A750 A442 controlled by the older newer transmission ecu, and that the car would not be drivable because of some misalignment. The solution was to leave the gearbox not connected, which gave me manual control with three gears to chose from on the A442.

I suppose that is your case, you would have similar problems with controlling the A442 if you changed out the engine and trans ECUs with the combined ECU from the newer car. Keeping the older ECUs and fixing the engine and IP control is probably easier. Might be only injector pressures to adjust, and change over the vacuum controlled air intake valve (instead of the electric one on the newer version).

As the engine ecu also supplies input to the instrument panel and other systems, I suspect that it's not that straight forward to swap over the ECUs and harness. Here I'm only guessing, but you might end up having to change "half the dashboard".

As said above, the A750 is far superior to the A442 when it comes to drivability and comfort, not the least because of better integration between engine and transmission control in the combined ECU. OTOH, the A442 is a solid box -- give it some synthetic fluid to give it slightly smoother shifts.

Edited: swapped out two words (strike-through).