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2G 95 GSX MT DSMLink Engine Wiring Harness Diagnostics

nix4

Probationary Member
15
3
Oct 15, 2013
Albuquerque, New_Mexico
Greetings,

I have a faulty engine wiring harness which causes my ignition to start correctly, but upon removing the key it never shuts down (checked relays and they seem fine so I suspect a bad wire or some short or error in the harness).

Does anyone have information on how to diagnose the 1995 GSX ignition system? Any information on services that restore harness or sell working ones (other than ebay) would be appreciated too!

Thanks
 

dustyboner

DSM Wiseman
1,635
776
Mar 13, 2016
abq, New_Mexico
have you check the ignition switch?
you can check the switch itself or backprobe pin 82 on the ECU. if you have voltage between pin 82 and ground with the key off, the problem is the ignition switch or the wiring between the switch and ECU.
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pin 82 and the fuel pump side of the MPI relay both get power from the ignition switch (IG1). So if it was a problem with the relay not deactivating, turning the key off would still kill the fuel pump and the car would shut off as soon as the fuel pressure dropped off.

most likely you just need a new ignition switch

I have a switch you can borrow if you want. That way you can just pull the column cover off, unplug the harness and plug in another ignition switch. Then use a screwdriver to operate the switch and see if it fixes the problem.
 

nix4

Probationary Member
15
3
Oct 15, 2013
Albuquerque, New_Mexico
Awesome, and thank you (took me a while to realize you are local to ABQ too!). Thanks for the info, its exactly what I needed... looks like ignition switches are available locally and are pretty cheap so I may just get a new one. I'll post here my results so its on the forums for future reference.
 

nix4

Probationary Member
15
3
Oct 15, 2013
Albuquerque, New_Mexico
Update: Looks like the issue may not be the switch. I get the wrong behavior (not turning off completely where battery, SRS and some other dash light remains on forever), when a relay is plugged in.

If the relay (under the dash by the ECU, part # E8T08474-E225), is REMOVED, car shuts off properly, but with it (or another relay E125) it doesn't shut down right.

We tested these relays and we think they are ok, but is this a pretty obvious indicator that they could still be bad?

Thanks
 

dustyboner

DSM Wiseman
1,635
776
Mar 13, 2016
abq, New_Mexico
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im pretty sure the number under the E8T08474 is just a batch number.

steve has a nice write up on the MPI relay HERE

The 2G ECU receives backup power on pin 80 from Junction Box fuse #19 (room) in the drivers footwell fusebox. This is used to maintain the RAM in the ECU's CPU and allow the ECU to power itself up. It also provides power to the radio to maintain it's settings and to the cabin lights. Like MPI relay input pins the backup power on ECU pin 80 should be present all the time. In other words it's unswitched.

The ECU sits dormant in a powered down state waiting to see pin 82 (IG1 from ignition switch) go high (to battery voltage). When the IG1 from ignition switch goes high the ECU pulls pin 38 low (to ground). This causes the the MPI/MFI relay to activate and switches the MPI power from the input to the output pins providing power to the ECU on pins 12 and 25 along with various sensors, solenoids, injectors, ISC, and O2 Heater in the engine bay.

Shortly after battery voltage shows up on ECU pins 12 and 25 the reset circuit in the ECU wakes the ECU up, the CEL will come on for about 5 seconds and then turn off, the boost gauge will display 0 (Stock ECU software on turbo cars) and the ISC on the throttle body will move in and out to rehome.

The next interesting condition is when ECU pin 71 (indirectly START from the ignition switch) goes high (to battery voltage) causing the ECU to do the things it needs to do the start the engine.

Once the engine is spinning (CAS is pulsing) the ECU pulls pin 8 (The Fuel Pump Control signal)) to ground and continues to hold it low until you turn the car off or the engine stops (CAS stops pulsing for 10 seconds), to keep the fuel pump powered.

if you don't have voltage at pin 82 on the ecu when the key is off,
- you can check to see if the relay contact is sticking. but if you tried another one, and it sill does it, thats probably isnt the issue. (i can let you borrow a good relay or check yours if you have doubts).

- To activate the relay the ecu grounds pin 38. so you should check that there isn't a short in the wire. with the key off just unplugg the relay and check for continuity between pin 6 (blue/green) and ground. if you have continuity, the wire is either shorted to ground or its being grounded by the ecu.

- pull the cover on the ecu and check for damage like burnt components or leaking capacitors.



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nix4

Probationary Member
15
3
Oct 15, 2013
Albuquerque, New_Mexico
Awesome, I also found that link and its perfect. I printed it out. I have two fusable links 100A and 60A that I need to replace (got new ones just need to install them), then its down to testing the relay...

If the relay is still good then my harness is bad somewhere..

Thanks for the info, its a big help. Car is very close to running but something caused the ECU to fail to get a tune on it, and a bad transistor is what was reported by the DSMLink poeple, so they repaired it and sent it back to me. Now, I need to find out why it wont shut off properly and the relay or the harness seems to be left...
 

steve

DSM Wiseman
13,871
938
Feb 3, 2002
Boulder, Colorado
- To activate the relay the ecu grounds pin 38. so you should check that there isn't a short in the wire. with the key off just unplugg the relay and check for continuity between pin 6 (blue/green) and ground. if you have continuity, the wire is either shorted to ground or its being grounded by the ecu.

If the wire from the ECU to the MPI relay (pin 38) was shorted to ground the ECU would always be powered. The feed to the MPI relay is supposed to be unswitched and the ECU via the relay spreads it around.
 

nix4

Probationary Member
15
3
Oct 15, 2013
Albuquerque, New_Mexico
Replaced fusable links in engine compartment fusebox for 60A and 100A. Tested ignition switch, when turned on it shows appropriate lights on dash but when removed some lights turn off (beeping stops), but BRAKE, SRS and Battery remain on. I think the relay is the only thing left, and I will see if I can order one.

This behavior dosnt occur if the relay is removed. So I believe that means the ignition switch is fine, though I can certainly diagnose using the information provided.
 

nix4

Probationary Member
15
3
Oct 15, 2013
Albuquerque, New_Mexico
UPDATE (Solved): With the help of a fellow member of these forums it was discovered one of the wires to the MPI Relay was permanently wired to "hot" and so the ECU never got the appropriate signal to shutdown. The harness (which was purchased off eBay) may not have been for a 95 and was instead for a 96+ DSM and thus had extra wires which did not line up with the 95's MFI Relay and it was modified to fit incorrectly.

Thanks to all to helped to sort this out.
 
Last edited:

KCDsmDude

Proven Member
278
143
Oct 11, 2020
Kansas City, Missouri
I have this SAME issue with my 2g, but haven't even looked into it. Take the key out and car still runs, have to pop it into first and kill it, then disconnect battery.

But I'll be using this thread as a starting point.
 

dustyboner

DSM Wiseman
1,635
776
Mar 13, 2016
abq, New_Mexico
That was what I was largely expecting.
Was it the signal from the ECU to the MPI relay that was ties to ground to keep the MPI power circuit active?
pin 3 on the single relay connector was connected to one of the (black/white) supply wires to the fuel pump relay.
so it had B+ at pin 82 being feed by the MPI

-----------------------
 

steve

DSM Wiseman
13,871
938
Feb 3, 2002
Boulder, Colorado
pin 3 on the single relay connector was connected to one of the (black/white) supply wires to the fuel pump relay.
so it had B+ at pin 82 being feed by the MPI

-----------------------

So once it was turned on the first time the ECU never saw the ignition switch off and it also back powered everything on the ignition circuit. It would have been easier to drag the 96+ MPI relay along with the harness during the swap.
 

nix4

Probationary Member
15
3
Oct 15, 2013
Albuquerque, New_Mexico
There were several factors that changed when I traded out my 92 TSI for the 95 GSX, I had since blown the 1g block and bought a new 2g block that was under warranty and had proceeded to build the project to be ready for tune. It was during tuning that things started going south, I lost dash guages and then in an attempt to fix that we started discovering various other small things that were shot and needed replacement. Due to the dashboard problem we got another set of harnesses off eBay and were able to restore the dash but then ran into this issue with the ECU and ignition. ECU was shipped off to ECMlink for diagnostics and they found a transistor that was blown, repaired it, confirmed it could save mappings and sent it back. I still had strange ignition behavior and it wasnt until I got help here that it was made clear the wiring to the ECU was setup wrong.

Ive been battling my DSM for over 5 years, ever since my TSI blew its automatic transmission and I choose to not rebuild it and instead trade it for a manual 2g. I traded into a structurally healthy car but electronically fraught with small issues all over. I believe I have replaced almost everything now so I'm excited to finally see this car running. If I can manage to get a steady tune out of it for a daily driver, then I can make it pretty and start attending local DSM group meets :)

By yes, in a perfect world I would have known more than I did then, and also would have had more support but I was just 1 dude and I knew nothing..
 
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