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Hello everyone, as the title says I am working on a 1991 Legacy LSi sedan with 4eat. I've done an engine swap with a 2.5 frankenmotor which was an adventure of its own, ending up with a haltech elite 550 and cleaned up wiring harness. The engine runs great but needs a little dyno time to get the ignition curve down which brings us to the current issue, the transmission only has park, reverse, neutral, and 3rd gear no matter what position the selector is in or if the manual button is engaged. The tcu is giving us the 16 flashes but will not output any codes after performing the secret handshake multiple times or when trying 2 different tcu's, one from a 93 fwd and one from a 95 impreza awd.

Any input would be appreciated, Thanks!

It has detected an electrical fault and put itself into what's basically limp mode, or the TCU can't even reach the trans.

You have three options, harness problem, connector problem or solenoids. My money would normally be on solenoids, mostly because these cars aren't known for harness problems and there's a reason Subaru put a filter on later iterations of that trans, but since you've just done an engine swap I think connectors or some incompatibility there like that is more likely. Maybe take a look at what you did to "clean" up the harness.

FYI it's perfectly safe to drive other than the poor acceleration and doing 4000rpm at 75mph not being ideal for the engine.

Thank you for your reply, the bit of harness that was cleaned up should have just been the engine sub harness, we found the cam and crank position sensor section to be damaged and repaired it. On the ECU side we depend the factory ECU plugs and put them into the haltech plug. I will let the shop know to continue checking for solenoid or transmission harness issues.

I believe the center diff is also binding up due to this, with that and the tuner not being comfortable really working the car on the dyno we're hesitant to drive it on the street.

So you've followed both procedures noted on my site to try and get codes from the TCU and still just get the 16 flashes?

https://www.surrealmirage.com/subaru/trans.html

Does the shop have the wiring diagrams to trace each circuit that is noted by the codes? That would be my first step if I was unable to get the TCU to give me its error codes.

I would find the pinout for the harness connectors on top of the trans and then probe them accordingly with 12v and ground if necessary in order to verify solenoid operation. The solenoids are loud enough to hear with the engine off.

I think you'll likely find that everything on the trans side is good and that some oversight in the engine bay is the source of your problem.

Resolved, the main transmission plug had a few pins come loose when the previous owner swapped it.

Glad you got it sorted and it was an easy fix.

Welp, after driving the car for some time and verifying my fluid level is correct, I have a large delay between when I shift to a gear and when it engages. This happens both when first taking off as well as when I come to a stop and take off again. Rpm makes a difference, cold starts/high idle it engages faster than once the car is at low idle after it has warmed up. It shifts fine between gears when driving but also seems to disengage and drop to neutral when coasting. I dont have any transmission codes so im unsure where to go.

Why do you say it seems to disengage and drop into neutral?

These transmissions lock the torque converter at cruise and it can seem like that.

When coasting the RPM drops down to idle RPM and when I get back on the throttle it will jump back up to about where the cruising rpm was, if I get back on throttle it definitely lunches like it's slamming back into gear.

I took a longer Drive yesterday and think I understand better what's happening, when coasting down to a stop it does not seem to be downshifting, it stays in gear to the point that it has to change and then it just drops to neutral until I get back on the throttle. It also seems that my torque converter is not locking up at Cruise.

Any chance you or someone riding with you could take a video of the tachometer while you're driving and upload to youtube so we can see what's going on?

Update, meant to attempt to do this but the transmission ended up bitting the dust in the mean time so now I'm swapping an 05 wrx 5 speed trans and rear diff in following Legacy777's guide.

Ok, let us know if you have any questions as you get into it.

Will do, be going a lot faster if I wasnt waiting on parts from the dealer because they said they had them in stock when they didnt. Only real issue i've run into so far is I am putting 06 sedan lateral links in the rear and switched to the 05 wrx rear axles, they fit perfect width wise but seem to be binding in the hub when I tighten down the nut.

Ok, yeah I'm not sure of compatibility between the two.

Looks like it was just rubbing on the dust seal, a little bit of shim stock and they are happy again. Rear end all put together, changed all the cam seals, mounted the flywheel, clutch, and pressure plate, ready to stab in the transmission after I punch the hole in the firewall for the clutch master cylinder.

Alright I've run into my second major issue which is I got a complete drivetrain from a 2005 WRX and the driveshaft is an inch or two short. From what I can find I want one from a 95-99 ish Legacy but have also seen reports of driveshafts from third gen Leg's (00-04) working but the measurements seem off. Would anyone be able to double check me here?

Just for clarity, where is it too short? In the front section where the driveshaft goes into the transmission or into the rear diff?

Legacy777 wrote: ↑Mon Mar 24, 2025 2:25 pm Just for clarity, where is it too short? In the front section where the driveshaft goes into the transmission or into the rear diff?

Transmission to carrier bearing is fine, carrier to rear diff is short.

I "think" you should be able to use an later model Legacy rear section driveshaft as long as it has the newer style rear diff.

Again, I think there was a crossover point in 95-96 where the Legacy transitioned from the older style diff to the newer style diffs.

We're gonna give it a shot, measurements say I need a 62" driveshaft, the manuals from 95 were 64" but the autos were 62" so I have a dorman/ultrapower 936904 coming in at Oriely's to compare.

Confirmed, the Dorman 936904, listed as being for 1995-2004 subaru Legacy automatics (according to Rockauto). It measures 62-1/4" overall, the shafts are the correct length from trans to carrier and carrier to rear diff, and it has the correct flange for the newer input flange.

Good deal!