How to use a TT ECU in your TT ATX

[Hannibalzero]

Well, that's what I did. So far I've been driving around on it for 2-3 days.

[chrisgtoman]

i just did that and I cant get it to start...I think i need a visual on how where to modify the harness....

[wukillabeez]

Is there any bugs/issues with using this method? or wil i be good to go after doing this?

[Hannibalzero]

Originally Posted by chrisgtoman

i just did that and I cant get it to start...I think i need a visual on how where to modify the harness....

Has anything else change since you last tried to start? Which wires did you cut spefically? Does the car crank at all?

[SLguy]

I just dug up some of my old information that I found in a thread I had posted a while back, and thought it may benefit some who view this thread. Here is how to convert a 94-95 diagnostic port to an OBDI for those converting their car to a 91-93 TT ECU so that all the datalogging equipment is plug and play.

First get a OBDI diagnostic port. Here's a picture of the OBDI port and its pin numbers, taken from stealth316.



Now here is how to wire it from my notes I made when I converted my 94 port to a 92 port.

1994 Pin #.....Wire Color.........1992 Pin #..........Purpose

Pin 6...............Y-R.................Pin 6.................ELC-4 A/T Control (ATX only)
Pin 1................P...................Pin 10................Query - ECS, ABS, ECM, A/T, AC
Pin 9...............B-L.................Pin 9..................ETACS Unit
Pin 11..............Br..................Pin 7..................Auto AC
Pin 3...............L-O.................Pin 3..................ECS Control Unit
Pin 14.............W-R................Pin 11.................Speed Sensor
Pin 8...............Y-R................Pin 4...................ABS Control Unit
Pin 12..............Y-B................Pin 8..................SRS Diagnostic Unit
Pin 13.............Y-B.................Pin 5..................Auto Cruise Control
Pin 4,5..............B..................Pin 12................Ground
Pin 7................Y..................Pin 1..................ECM-MPI Functions


Color code:
Y: Yellow
R: Red
P: Purple
B: Black
L: Lavender (Blue)
O: Orange
W: White

[RL7]

3 questions:

1) If you don't mind altering your harness, is the "wiring harness adapter" necessary? Seems you should be able to disconnect/cut and cap wires at the ecu without issue.

2) Probably doesn't matter, but pin 103 is VICS sensor on NA and active exhaust switch on turbo. Disconnect?

3) If you just connected harness 71 to ecu 51, grounded ecu 71, spliced harness 56 into ecu 55 and 56, and cut 7, 103, and 111, shouldn't that do the trick? Seems that all other wires (21, 59, 102, 105, 109, 110, 116) are only used on one side (ecu or harness), so does it really matter if you cut or disconnect them?

[SLguy]

Originally Posted by RL7

3 questions:

1) If you don't mind altering your harness, is the "wiring harness adapter" necessary? Seems you should be able to disconnect/cut and cap wires at the ecu without issue.

2) Probably doesn't matter, but pin 103 is VICS sensor on NA and active exhaust switch on turbo. Disconnect?

3) If you just connected harness 71 to ecu 51, grounded ecu 71, spliced harness 56 into ecu 55 and 56, and cut 7, 103, and 111, shouldn't that do the trick? Seems that all other wires (21, 59, 102, 105, 109, 110, 116) are only used on one side (ecu or harness), so does it really matter if you cut or disconnect them?

1. The harness adapter are for people who don't want to hack into their harness incase they decide they want to reverse it without any problems. There's nothing wrong with not using it, i'm not.

2. Cut it, its not needed.

3. Leave pin 51 alone, its already connected the way it should be. Cut 71 on the ECU side and ground it, cap the loose wire off, it goes to nothing. You can splice 55 into 56, but I bought a 2nd O2 sensor and actually running an O2 sensor for each bank, you should get a better ECU response that way, but you can just splice them in if you want. Cut 7, 21, 59, 102, 105, 109, 110, 111, 116 and just cap them off or something, they aren't needed.

[RL7]

Originally Posted by BigTyla

...... The hardest part was figuring out what to do with the park/neutral position switch wire. After that the car ran miraculously.

.....
Note that I left the park/neutral position switch wire alone. This wire is now going into an input in the TT ECU designated for the starter relay signal. The car will still start as normal. Without the p/n position wire going into this input, the car will have very erratic timing when you shift into drive. I learned this the hard way, and it took me weeks to figure out the reason behind it.

.......

If that is the case, I will need some clarification of the above. I took it to mean harness pin 71 (p/n position) goes into ecu pin 51 (m/t starter relay input). If that is incorrect, then what does it mean?

And for all the other pins that are unnecessary, I know they can be cut, but do they have to be cut? If they do nothing, can't they just stay there? I would think the less cutting, the better.

Quick edit: I was thinking down the same track and was going to run 2 O2s, but I noticed my rear "pre-cat" is jdm and does not have a place for an O2, so I figured, screw it. I think I'm going to just run a single wideband at the end of the downpipe.

[SLguy]

Originally Posted by RL7

If that is the case, I will need some clarification of the above. I took it to mean harness pin 71 (p/n position) goes into ecu pin 51 (m/t starter relay input). If that is incorrect, then what does it mean?

And for all the other pins that are unnecessary, I know they can be cut, but do they have to be cut? If they do nothing, can't they just stay there? I would think the less cutting, the better.

Quick edit: I was thinking down the same track and was going to run 2 O2s, but I noticed my rear "pre-cat" is jdm and does not have a place for an O2, so I figured, screw it. I think I'm going to just run a single wideband at the end of the downpipe.

He's saying that once you have the TT ECU plugged in, park/neutral sensor is going into the TT starter relay pin, so don't modify it. The ATX has a park/neutral switch (pin 51) and a starter relay signal (pin 71) and on the TT ECU the starter relay is pin 51. He originally put the ATX starter relay signal into the ECU starter relay pin, but due to the way the ATX wiring is, you need the park/neutral switch into the starter relay pin instead, otherwise it will start and run fine, but when you take it out of park or neutral you will have bad engine timing.

The only one thats imperative to cut is pin 71, and that needs to be grounded (on the ECU side). If I remember correctly, I didn't cut any of the other ones. Just make sure you don't have an N/A plenum with the VICS harness attached, and that should do it.

[RL7]

Ah, thanks, now it makse sense.
So simplified way to use TT ECU in ATX (1st gen):

1) Cut 71
2) Cap harness 71
3) Ground ECU 71
4) Splice 55 into 56 for one O2 in downpipe or run front bank O2 to 55 and rear to 56 (plus power and grounds to O2s)


That is much easier than I thought it would be. Almost too easy....