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1G 1991-1994 ecu swap into a 1990 DSM ignition wiring

This article presents the procedure for the ignition system wiring changes when swapping a 1991-1994 ECU into a 1990 car with a 90 wiring harness, gauges, and coil.
This procedure corrects the tach signal so your tach works with a 91-94 ECU. This procedure was covered on the KeyDiver web site which I give full credit for presenting the original wiring schematics.
The procedure has been removed from the site and this article is provided to replace it. There is another procedure used for the ECU swap ignition wiring but that way is much longer and requires many more parts.

converting a 1990 to a 1991-1994 ECU system

For this process the only part needed is a power transistor from a 1991-1994 2.0 engine (N/T or Turbo).

The 1990 coil plug has 4 wires coming out of it where as the 1991-1994 plug only has 3. The color of the wires on the 90 coil plug are as follows from the back of the connector.

1 2
3 4

1=Yellow/Black
2=Yellow/Green
3=White
4=Black/White

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These two pictures show the 1990 coil pack connector and the four wires used.

The 1991-1994 power transistor (#J722T) has 8 pins while the 1990 power transistor (#J122) only has 6. The wire colors for the 91-94 are as follows from the back side of the PT.

1 2 3 4 5 6 7 8

1=Yellow/Black
2=Yellow/Red
3=Black
4=White
5=No wire
6=Black/White
7=Yellow
8=Yellow/Green

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On the left is the 91+ PT and on the right is the 90 PT.

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These two pictures show the 91+ PT and its wires.

The 1990 wiring harness is almost identical in the engine ignition area as compared to the 1991-1994. The wires needed from the harness are originally go to the power transistor the colors are as follows.

1=Black
2=Yellow/Red
3=Yellow
4=Yellow/Green
5=Yellow/Black

The first wires that need to be connected are the thick gauged Black/White wires on the power transistor plug and the coil pack plug. The transistor's wire needs to be spliced into the coil plug's matching wire. That is the only wire on the coil pack plug that needs to be changed the rest are untouched.

Then the 1, 2, 3, 7, and 8 wires on the 1991-1994 power transistor have to be connected to the corresponding colored wires on the 1990 wiring harness.

The next wire that needs to changed is the 4th wire on the power transistor, this wire needs to be lengthened to reach inside of the car so it can connect to the ECU. The wire needs to replace the 109# pin out wire, the ignition pulse detect, the existing wire that was in the 109# spot is to be left unconnected. The 6# and 14# pin out wires on the ecu need to be swapped also. This is a link that shows the pin out location and #'s on the ECU.

1G ECU Pinouts


If you have any questions or comments feel free to PM me at any time. Please remember to rate my tech article.
 
Last edited by a moderator:

steve

DSM Wiseman
14,602
1,482
Feb 3, 2002
Boulder, Colorado
Since it might help people understand what's going on, allow me to add the functions to the wire colors.

90 Coil Pack

1=Yellow/Black Power Transistor Collector Coil B (2&3)
2=Yellow/Green Power Transistor Collector Coil A (1&4)
3=White Tach Gate output (to noise filter and ECU)
4=Black/White +12v IG1 (Switched Battery Voltage)

My references show a different wiring for the 90 Power Transistor Module

1=Yellow/Green Collector 1 (OC1) Coil A
2=Yellow Base 1 (IB1) ECU pin 54
3=Black Ground
4=NC
5=Yellow/Red Base 2 (IB2) ECU pin 55
6=Yellow/Black Collector 2 (OC2) Coil B

And a different wiring for the 91+ Power Transistor Module

1=Yellow/Black Collector 1 (OC1) Coil B
2=Yellow/Red Base 1 (IB1) ECU pin 55
3=Black Ground
4=NC
5=White Tach Gate output ECU pin 109 and Gauge Cluster
6=Black/White +12 IG1 (Switched Battery Voltage)
7=Yellow Base 2 (IB2) ECU pin 54
8=Yellow/Green Collector 2 (OC2) Coil A

You'll note that the wire colors match but they switched which of the two transistors was used in the PTM.

The 90 gauge cluster is driven from the output of the noise filter. You need to retain it unless you swap to the later cluster. It should be bolted to the intake manifold somewhere.

The 91+ ECU should now get it's tach signal from pin 5 of the 91+ PTM.
 
Last edited:

spoonman

Supporting VIP
864
27
Jul 20, 2007
Omaha, Nebraska
N/T, The normal (turbo) ecu swap wiring will not work with the 2.0 naturally aspirated engine's wiring harness and a few steps must be changed for the swap to work correctly.

Non turbocharged DSM's use the same ignition system as turbocharged DSM's and the wiring for the power transistor and coil are identical. The difference is that the N/T ecu and wiring harness do not use the (air flow sensor reset) pin which is only used with turbo MAF sensors and connects to the ecu at pin 14 on 1990 ecu's and pin 6 on 1991-1994 ecu's. To correct this you must remove the 6 wire from the ecu harness connector and insert it into the 14 slot of the connector. If you do not switch the wires your car will have trouble deciding if you are in decel mode and will make your engine stutter at low RPM decel.
 

steve

DSM Wiseman
14,602
1,482
Feb 3, 2002
Boulder, Colorado
The difference is that the N/T ecu did not change its wiring pinouts after 1990 like the turbo ecu, so the 6 and 14 pinouts on the ecu do not have to be switched.
I don't think so. Just like with the turbo ECUs the IPS switched location between the 90 and the 91+ ECUs based on every one I've looked it. So yes, you don't swap both 6 and 14 but you do move pin 6 to 14 on an NT car when mixing cars and ECUs.

You may also notice that the N/T wiring harness and ecu do not use the 14 pinout as it is for an extra wire (idle switch) on the turbo MAF sensor that the N/T does not use.
It's the MAF reset signal (Green/White) that the NT ECUs don't have/use. That's the signal on pin 14 on the 90 ECUs not the IPS. The IPS (Green) is a key input for managing idle speed, dashpot control, and deceleration fuel cut on both the NT and turbo ECUS. It's on pin 6 of a 90 ECU and pin 14 on the later versions.
 
Last edited:

steve

DSM Wiseman
14,602
1,482
Feb 3, 2002
Boulder, Colorado
Blackfuse said:
The 4 pin coil pack connector has a white cable called "Tach Gate output (to noise filter and ECU)" if I'm not wrong this currently goes to pin 109 only. Does it split to some where else?

If you look closely, you'll see I say it goes to the ECU and gauge cluster.

Blackfuse said:
Continuing with the main question, After I change the PT from a 90 to a 91+, I have to connect the white cable from the 91+ PT to the Pin 109 in the ECU, by cutting the current cable in pin 109.

The question is, can I cut the white cable from the 4 pin coil pack connected and use it to transmit the signal from the white cable in the reciently swapped 91+ PT connector?

No you can't, you still need the 90 style Tach Gate driver on the coil pack to operate the 90 gauge cluster. The whole reason for the swap like this is to fix the problem with the tach in the gauge cluster acting up when a 91+ ECU is swapped into a 90 car.

The solution is to continue feeding the tachometer gauge with the original circuit from the coil pack and use the new signal from the power transistor to feed the ECU what it expects.
 

Paintballaa5

Proven Member
519
189
Jan 23, 2012
Houston, Texas
This article is great, but I’m having a hard time understanding exactly what to do with step 1- the black/white wire. I assume it still has to power the coil, so when it says to splice the b/w wire from the coil plug to the 91 PTU, does that mean to T it off from the harness to the PTU?

We’re not cutting it and putting it to a new location, just splitting off to power the PTU?

I’ve seen this question asked in a few threads but no definitive answers yet. Updating this would prove useful to new guys who run into this thread.
Thanks!
 

Breadvans

Proven Member
123
11
May 16, 2021
Harrisburg, Oregon
This article is great, but I’m having a hard time understanding exactly what to do with step 1- the black/white wire. I assume it still has to power the coil, so when it says to splice the b/w wire from the coil plug to the 91 PTU, does that mean to T it off from the harness to the PTU?

We’re not cutting it and putting it to a new location, just splitting off to power the PTU?

I’ve seen this question asked in a few threads but no definitive answers yet. Updating this would prove useful to new guys who run into this thread.
Thanks!
You are supposed to t it off correct? That was my understanding
 

steve

DSM Wiseman
14,602
1,482
Feb 3, 2002
Boulder, Colorado
Correct - b/w wire from PTU T's into the c/w coil wire.

I think you mean the black/white wire from the pin 4 on the coil connector to the black/white wire on pin 6 of the PTU.

You all are correct that the PTU needs switched +12v just like the coils do. Where you get it and how you route it is an exercise left for the student. Just be sure to keep the condenser in the circuit by the coils.
 
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