N/A vs Turbo TCU differences?

[Binford]

Long story short I swapped the motor/tranny from a '93 SS into my '90 LS this weekend. I topped off the tranny with ATF but it doesn't shift out of first gear. If I select the "manual" mode it will shift. I drove the '93 SS over 50 miles last week before the swap and everything worked perfectly. Are there any differences in TCU's or the wiring? Everything plugged right in. Also, I'm running it on the N/A '90 LS ECU if that makes a difference. I plan to tackle that part of the swap at a later date as I don't have the time right now. It runs good (although rich ) the way it is.

[AWD_addict]

I've used TCUs from NA and turbo cars back to back in a '90 L. Both worked fine. Unless you damaged it, I doubt the TCU is the problem.

[Binford]

Thanks, I'll double check everything is plugged in good and tight, and probably run another ground just to be sure. Otherwise I'm lost on this deal.

[Binford]

I still can't figure this out. I double/triple checked everything. I did swap TCUs just to be sure , especially since that is an easy thing to check. One thing to note is one of the TCUs had "FF" on it in big letters and the other had "HU" on it. Not that it made any difference.

Anybody have any other ideas? I know for a fact the ATF is topped off. ECU shouldn't matter, right? I have the rear part of the driveshaft removed with the "FWD" fuse installed becuase I'm having difficuly with the donor car not wanting to give up its rear diff. I've driven another auto with the "FWD" fuse installed so this shouldn't cuase any problem like this, and I don't see the missing half of driveshaft cuasing shifting problems either. HELP!

[b3lha]

Can you please tell me which car the FF TCU came from?

FF is the same TCU code as a Euro/Aussie SVX. This car has the VTD transmission rather than the ACT4 transmission normally found on US models. It would be very interesting to know if you have found a US model with the VTD box. It is far superior to the ACT4 box.

You must use the correct TCU for the box you have installed. The Euro VTD box has Vehicle Speed Sensor #2 inside the trans instead of in the front diff. It's a different type of sensor producing a different type of signal. The FF TCU requires this type of signal.

The speed sensor wiring is different and this is probably the cause of your problem. Check the TCU wiring of your car and the donor car.

On the ACT4 box, the signal wire from VSS2 (in the front diff) goes to pin a11 of the TCU and also feeds the ECU/cruise/speedo etc.

On the VTD box, the signal wire from VSS2 (inside the trans) goes to pin a17 of the TCU. Then a wire comes out of pin c6 and feeds a modified signal into a11, it also feeds the ECU/speedo/cruise etc.

[b3lha]

I have the rear part of the driveshaft removed with the "FWD" fuse installed becuase I'm having difficuly with the donor car not wanting to give up its rear diff. I've driven another auto with the "FWD" fuse installed so this shouldn't cuase any problem like this, and I don't see the missing half of driveshaft cuasing shifting problems either. HELP!

If this is a VTD box, as I suspect from the TCU code, then the fuse is "DIFF LOCK" not "FWD".

Also, check the diff ratio (sticker on the rear diff). I think the ratio is 1.370 for VTD and something else for ACT4. If you have mismatched ratios front and back it will cause big problems.

The TCU decides when to shift based on vehicle speed and throttle percentage. If it is not shifting then it could be that the TCU is getting incorrect data for one of these parameters. Most likely because of incorrect speed sensor wiring.

[wtdash]

I did this exact swap ('93 SS EJ22T into '90 NA), but have a '91 Turbo 4EAT. I used the SS ECU (must swap cam/crank and of course add turbo sensors) and the '93 Turbo TCU.

I know from experience that the '91 Turbo TCU was wired different than the '93 turbo TCU(Power Mode mod). As is the '90 TCU.

All the TCU's shifted thru the gears normally, though.

Have you tried to pull codes from the TCU/ECU?

Td

[Binford]

Can you please tell me which car the FF TCU came from?

FF is the same TCU code as a Euro/Aussie SVX. This car has the VTD transmission rather than the ACT4 transmission normally found on US models. It would be very interesting to know if you have found a US model with the VTD box. It is far superior to the ACT4 box.

You must use the correct TCU for the box you have installed. The Euro VTD box has Vehicle Speed Sensor #2 inside the trans instead of in the front diff. It's a different type of sensor producing a different type of signal. The FF TCU requires this type of signal.

The speed sensor wiring is different and this is probably the cause of your problem. Check the TCU wiring of your car and the donor car.

On the ACT4 box, the signal wire from VSS2 (in the front diff) goes to pin a11 of the TCU and also feeds the ECU/cruise/speedo etc.

On the VTD box, the signal wire from VSS2 (inside the trans) goes to pin a17 of the TCU. Then a wire comes out of pin c6 and feeds a modified signal into a11, it also feeds the ECU/speedo/cruise etc.

I'm at work today so I'll find out tonight which is which. You bring up an interesting thought on this. I'll compare wiring between the two tonight also. I was already planning on pulling codes tonight.

[Binford]

I have the rear part of the driveshaft removed with the "FWD" fuse installed becuase I'm having difficuly with the donor car not wanting to give up its rear diff. I've driven another auto with the "FWD" fuse installed so this shouldn't cuase any problem like this, and I don't see the missing half of driveshaft cuasing shifting problems either. HELP!

If this is a VTD box, as I suspect from the TCU code, then the fuse is "DIFF LOCK" not "FWD".

Also, check the diff ratio (sticker on the rear diff). I think the ratio is 1.370 for VTD and something else for ACT4. If you have mismatched ratios front and back it will cause big problems.

The TCU decides when to shift based on vehicle speed and throttle percentage. If it is not shifting then it could be that the TCU is getting incorrect data for one of these parameters. Most likely because of incorrect speed sensor wiring.

Installing the fuse turned on the "FWD" light on the dash, though I suppose the "DIFF LOCK" light is in the same place in the cluster.

I realize I cannot run two different ratios which is why I pulled the driveshaft so it's no longer mechanically linked. The rear diff ratios are 3.9 on the Turbo, 4.11 on the N/A.

[Binford]

Sorry it took so long to get back to this. I was mistaken. I did not have an "FF" TCU, it is an "EE" out of the N/A. The SS has an "HU".

I did encounter another weird issue, also. I got the entire rear subframe swapped over since I couldn't get just the diff out of the SS. I read on here somewhere that the rear speed sensor in the tail shaft housing was responsible for shifting so I figured since I didn't have the driveshaft hooked up, that sensor wasn't getting any signal. So I took it for a test drive once I got everything back together only to find it still didn't shift. Here's the odd part: I realized I still had the "FWD" fuse in and when I removed it, it shifted perfectly! WTF?!

On top of that, it now seems to be only front wheel drive! I know the AWD worked amazingly well before the swap. At least I can drive it now, though, but I gotta get this figured out!

[b3lha]

Sorry it took so long to get back to this. I was mistaken. I did not have an "FF" TCU, it is an "EE" out of the N/A. The SS has an "HU".

OK. Scratch everything I said about VTD then.

I did encounter another weird issue, also. I got the entire rear subframe swapped over since I couldn't get just the diff out of the SS. I read on here somewhere that the rear speed sensor in the tail shaft housing was responsible for shifting so I figured since I didn't have the driveshaft hooked up, that sensor wasn't getting any signal. So I took it for a test drive once I got everything back together only to find it still didn't shift. Here's the odd part: I realized I still had the "FWD" fuse in and when I removed it, it shifted perfectly! WTF?!

On top of that, it now seems to be only front wheel drive! I know the AWD worked amazingly well before the swap. At least I can drive it now, though, but I gotta get this figured out!

Have you tried checking for TCU error codes?

[ciper]

b3lha Can you provide me with some sort of document to prove the SVX in other regions had the VTD differential? I have been arguing this for years and the idiots on Nasioc can't accept that the impreza was NOT the first car with the better center differential.
I originally found this out because someone has a drag racing forester and was able to easily swap the two tail shafts with no modification to the transmission itself. Yes they are phase 2 4eat

I assume you live outside America? Do they have junk yards where near by? Would you be able to grab a tailshaft from a phase 1 VTD 4eat? I'd like to try an mpt to vtd conversion.

On a separate note i believe you are incorrect about the VTD TCU not being able to function with an MPT differential. I know for a fact that the phase 2 VTD and MPT differentials are interchangeable along with there TCU. The lockup may not be at the best points but they do function.

From what I know the speedo cluster outputs a signal just like the electronic sender mounted externally on MPT AWD and 2wd 4eat which outputs a signal just like the five speed manual and six speed sti trans. On cars with an electronic speedometer the TCU does a conversion based on final drive to give the right speed display.
I would be willing to bet money that the VTD 4EAT on the SVX and the MPT 4EAT are the same transmissions forward of the tail section.

[b3lha]

b3lha Can you provide me with some sort of document to prove the SVX in other regions had the VTD differential? I have been arguing this for years and the idiots on Nasioc can't accept that the impreza was NOT the first car with the better center differential.
I originally found this out because someone has a drag racing forester and was able to easily swap the two tail shafts with no modification to the transmission itself. Yes they are phase 2 4eat

This thread on the SVX network contains a link to, and translation of, a japanese document
http://www.subaru-svx.net/forum/showthr ... post485067
I have three JDM SVX in my driveway with VTD. Two of them manufactuered in 1991.

I assume you live outside America? Do they have junk yards where near by? Would you be able to grab a tailshaft from a phase 1 VTD 4eat? I'd like to try an mpt to vtd conversion.

I am in England. Older Subarus are rare here, especially automatics. I think the SVX was probably the first VTD and only 224 were ever sold. I can't even find parts for my own cars.

On a separate note i believe you are incorrect about the VTD TCU not being able to function with an MPT differential. I know for a fact that the phase 2 VTD and MPT differentials are interchangeable along with there TCU. The lockup may not be at the best points but they do function.

I'm not sure I understand what you mean. If you use the correct TCU for the transmission, then it should work fine, except for wiring differences.

For USDM units, the wiring is all the same. But the European and Aussie box has a different type of speed sensor to the JDM and USA box. The wiring is different and the two types are not easily interchangable. That's what I was referring to above because the code "FF" that the OP originally mentioned is for a European TCU.

As for using a VTD box with a MPT TCU, or vice-versa. People have done it, and it's drivable and the AWD doesn't work properly. The amount of drivability varies because some VTD boxes use a N/C C solenoid and some N/O.

If you have a look at the website in my sig, you'll see that I've reverse-engineered much of the TCU programming, shift maps, torque converter maps, etc. I haven't figured out the AWD lockup code yet, but there are certainly important differences between MPT and VTD.

From what I know the speedo cluster outputs a signal just like the electronic sender mounted externally on MPT AWD and 2wd 4eat which outputs a signal just like the five speed manual and six speed sti trans. On cars with an electronic speedometer the TCU does a conversion based on final drive to give the right speed display.

I don't know how the Legacy speedo works. Is it cable driven? On a JDM or USDM SVX, speed sensor #2 (in the front diff) supplies a square ware to the ECU, TCU, Speedo and several other units. On a Euro or Aussie SVX, speed sensor #2 (inside the gearbox), supplies a sine wave to TCU. This is not compatible with the ECU or Speedo. The TCU modifies the sine wave into a square wave and feeds it to the ECU and Speedo. The speedo cluster doesn't output anything.

I would be willing to bet money that the VTD 4EAT on the SVX and the MPT 4EAT are the same transmissions forward of the tail section.

Yes, they are very similar. I know someone who has fitted a VTD tail onto his MPT box and I'm currently programming a custom TCU for him.