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Chad's '86 to '88 ECU conversion (fixed)

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#1 Boosted77.


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Posted 13 September 2014 - 03:12 PM

Helloo from a long time no see member.  Boosted77 here.  I needed to use Chad's info recently that has been messed up due to a font error that stems from (i think) when the site was hacked several years ago.


Here's the topic with the content fixed so that it can be a little more easy to read:

86 TSI: AŁ connector

1: IGN - (negative)
2: AFS
3: n/c
4: GND (AFS)
5: Intake temp
6: Coolant temp
7: Idle SW
8: Motor Position SW
9: Pressure to gage
10: +5 volt power
11: O2 sensor
12: Ignitor signal
13: n/c
14: n/c
15: TPS
16: n/c
17: Intake temp (OVCP)
18: n/c
19: speed (coil)
20: n/c
21: Diag. Output
22: control relay (fuel pump)
23: secondary air (for catalyst)
24: pressure solenoid

86 TSI B connector:

1: +12V
2: GND
3: GND
4: EGR
5: IGN (cranking)
6: AC relay
7: +12V
8: Inhibitor
9: ISC + (out)
10: Injector # 1
11: ISC - (in)
12: Injector # 2
13: +12V backup

88 TSI A connector:

1: IGN - (negative)
2: AFS
3: Motor position SW (from A 8)
4: GND
5: Intake temp
6: Coolant temp
7: Idle SW
8: n/c
9: n/c
10: +5 volt power
11: O2 sensor
12: ISC - (in) from B 11
13: Ignitor advance
14: Sensor +5 backup
15: TPS
16: Barometric sensor (New wire run to AFS from '88 ECU)
17: n/c
18: n/c
19: Speed (coil)
20: secondary air (catalyst)
21: Diag. Output
22: control relay (fuel pump)
23: ISC + (out) (from B 9)
n/c   Â  Â  Â  Â  Â 24: AC relay

88 TSI B connector:

1: +12 V
2: GND
3: GND
4: EGR
5: IGN (cranking)
6: AC switch
7: +12 V
8: inhibitor
9: Boost guage
10: Injector 1 (primary)
11: Ignitor signal (from A 12)
12: injector 2 (secondary)
13: +12 V backup

since a different MAS is needed to convert, you may as well step up to a 1-G DSM MAS, they are cheaper and work quite a lot better.

86 AFS to DSM AFS:

new > A 16 to green/yellow
new > +12 Switched to red


n/c means no connection

>From A 8 means remove from stock 86 connector and relocate to the 88 pin number

>On two pins, you will have to cut the wires and solder on the pin from the A or B connector, these connectors use different pins, you will have the pins you need when you start to move them.  Some move from A to BŁ, and some from B to A.  Some leads may be left over, these are pins not used (if you eliminate the secondary air and the stock boost gage)

This conversion also requires an 87/89 ISC assembly.  The new ISC requires a +5 V supply and a ground for the new functions,  because the MPS converted from a simple switch to a potentiometer, you need 2 additional wires.  However, the mitsu engineers decided to add 3 wires instead, and the 3rd is un-used at the ISC end, it is the blue/yellow and literlay has no physical connection at the ISC end, either in the ISC nor in the connector itself so don't bother with it.  

looking at the diagrams, it shared the common ECU ground in 87/89's, so ground it anywhere.  same for the +5 V, it connects to a common supply, so just find 5V at the ECU or at some other component like the TPS which is just inches away.

So here's what you need to do:

looking at the 87 ISC, you have a connector that has black/red, black/green and black/blue, this is the motor and idle SW.  It connects as follows to the 86 harness:

87 ISC motor :

87 ISC black/red    to   87 harness yellow/black  (splice here) to 86 harness  green/white

87 ISC black/green to   87 harness yellow/lbue  (splice here)  to  86 harness black/yellow

87 ISC black/blue   to   87 harness yellow/red (splice here)  to 86 harness yellow/red

now you have the 4 pin connector with green/red, blue/red, black, and blue/yellow, this is the new MPS circuit and connects as follows:

87 MPS:

87 ISC red to   87 harness green/red (splice here)   to  new +5 volts  
87 ISC green  to  87 harness blue/red   (splice here)   to  86 harness green/black
87 ISC black  to   87 harness black   (splice here)   to  new ground

87 ISC red jumper  to   87 harness blue/yellow   to   N/C  <  don't mess with this one

leave the pins at the ECU where they are, they are correct, you simply need to add the 87 ISC, splice the 87 harness to the 86 harness where is says "splice here", and wire in the +5 and the ground

To complete this conversion it would help to look over the '86 and '88 electrical scematics.

Lastly to count the pins start from the Large "A" harness and contains the large white wire which is the ignition coil negative (on the front and left of the harness plug while facing down) and count to the right then horseshoe around to the next closest wire on the second row.

Enjoy and sticky!

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#2 JAinsworth


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Posted 13 September 2014 - 03:21 PM

Thanks for this.  I'll move it to the FAQs

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