Inadvertently ran MS unit with main connector loose, now won't start.

This is on my Thunderbird, but I figure there are plenty of knowledgeable folks here who might have some insight.

The MS unit in question is an old V2.2 MSnSE set-up I built for my TBird probably 15 years ago. I recently had the car off the road for a while doing a bunch of work. I recently got everything back together and restarted and pulled the car out of the garage yesterday.

I'd fired everything up a couple weeks ago and let the car run for a bit, but wasn't ready to get it out of the garage until this weekend.

I fire the car up and tweak with a few warm-up settings and then get it out of the garage. The toddler and I go for a quick putter around the block as an easy shakedown run (New custom rear suspension, rebuilt diff, etc, listening for noises). We get back, I shut the car down and prep to leave for a longer drive.

Car fires up and runs fine for the 6-mile drive. No weirdness, and nothing looks amiss on the laptop.

Get back. Park the car in the drive to give it a quick bath. Shortly afterwards, I go to start it, and I don't hear the FP prime. Hit it again, no prime. Try and start it a few times, it cranks, but doesn't fire. The pump is kinda noisy, so it's no mystery when it's running.
After a few tries, I give up and we (dejectedly) push it back into the garage. While doing so, I remember that I probably didn't snug down the db37 connector when I stuck the ECU back in the car. I go and correct that, but still no luck.

I did a little poking around and here's a couple things I found.

- The "Injector" LED on the case is flashing, even when the ECU is off. Dim flashing. LED goes full solid when key in "RUN" position.
- The ECU stays connected to the laptop (In Tuner Studio), even when the key is "OFF" and the ECU is supposedly "off" (It'll cycle connection when trying to start the car)
- The car has one of the MS Relay Boards in it. The Main Relay switches when the key is turned to "RUN" and I hear the FP relay click, but no prime. The relay for the FP is good and sees power.
- At the Relay Board, the injector fuses are seeing between 3-8V with the key in "OFF".
- I was just checking things a little bit ago, and when I turn the key to "RUN", my Odyssey battery is making a high-pitched sound.


Trying to figure out what the hell happened in the time it took me to wash the car. The car was running perfectly fine right before that.

Any thoughts?

The fact that your lap top connects to the MS is a good thing. Highly unlikely that the processor is cooked. It is also not obvious how a loose DB37 connector could cause damage to the MS. The fact that the laptop stays connected to the MS with the power supposedly switched off suggest to me that you have an external wiring problem outside of the MS box. The loose DB 37 connector was likely incidental; but, it would be good to check for damaged pins and any shorting on the wiring on the solder side of the main connector. If that reveals nothing, I would start with checking to see why you still have power on the +12 V supply (pin 28) to the MS when the key is off (which is what is enabling you to keep your laptop connected). Note that you don't need full 12v for the MS to operate. The MS will probably continue to operate down to a voltage or around 6 - 7 volts. If your 'quick bath' involved hosing down the engine compartment you may have developed a sneak circuit through an insulation failure caused by the application of water.

If you have a Jim Stim you could pull your MS box and connect it up to the Jim Stim and your lap top to confirm that the MS box works as it should. That would definitely point you to a problem with your vehicle wiring.

There was no wash-down of the engine bay. Just getting rid of a couple years of "garage dust" off of the outside.

The connector was loose, but still mostly engaged in the pins, but it was worth noting.

I made some external (power) wiring changes during this downtime as well. I replaced all of the fusible links in the car (3-4) with MAXI fuses and got rid of a couple in-line fuse holders for a couple of circuits (such as MS 12V power and a stereo feed). All of the fusible links were "Always Hot" circuits.
I also added a WBO2 (Spartan 2), and the heater and controller grounds are separated.

It *is* almost like something is backfeeding the unit, seeing as the injector circuits in the relay board are seeing some voltage (3-4V) when the key is off. The battery noise when I turn the key to "RUN" is odd too, also leading to something external from the ECU.

I pulled the ECU and connected to the Stim, and it seems to connect and operate like it should.

It's unlikely that a loose DB-37 could have caused damage. I'd look elsewhere.

If the ECU is still unplugged, do you hear the noise when in run? What is the voltage on the relay board / injectors?

If you've plugged the ECU back in, try switching the ignition to run and either pull the main fuse from the relay board, or pull the main relay from the relay board. Any weird noise? Any voltages on the relay board / injectors?

Any other changes: Did you change where the relay board gets the ignition switch signal from? Where the radio power is wired? LED dash bulbs?

I remember waaay back when I added an e-fan to my 245. And hooked it up to the fan output. I forget if I added the fan control circuit or not. But a typical e-fan circuit - relay with switched 12V on one side of the control circuit, and the wire leading to the MS to turn the fan on by grounding. And it turned out that the 12V going through the relay was enough to 'sort of' keep the MS powered up[ when the key was off. Since it didn't get a nice clean shut off, it would do weird things. I forget the exact symptoms, but it was something similar. Maybe some lights on with the key off, got me on the track of thinking about back-fed current supplies.

I ended up putting another relay in between the fan relay and MS - switch on and off by the ign key. When the key was on - it would close and connect MS to the fan relay, when the key was off, it would disconnect so MS wouldn't get back fed. And it went back to working properly again.

John, I was coming back here to basically say what you just described. I reinstalled the ECU and messed with a couple things, and that battery noise had gone away. I did notice that the injector LED was still dimly flashing. However, I did get a prime when I turned the key to "RUN". After doing that, the LED would be brightly lit and stay so until I cycled power again. The car actually started and ran when I tried a second time.

Still, after shutting the car off, that LED was still dimly flashing. I would see 3-4V on the injector circuits in the relay board when the ignition was OFF. They would jump to 12V when priming, but then drop back to 8V when the ignition was turned back OFF.

I pulled ALL of the fuses and relays from the relay board. That light never changed.

OK, so I went to the new wiring layout.
THIS is the layout from the supplier of my new relay box (lighting& fan).
I pulled Fuse #1...and the LED went out. With that out, the system cycled prime and started like it should, and there was no voltage present on the injector circuits.

I'm using that Black/Yellow trigger wire to connect to my old fan control circuitry and connecting it to my old trigger out of the MS box (Using X2). Previously, this trigger was connected to an external relay, and I had the diode (shown HERE) connected between the trigger and 12V around the relay coil out at the relay. I never had an issue.
When I redid things, I pulled that diode into the case on the protoboard I had the rest of the fan control circuitry installed. Now it seems that power is being back-fed into the ECU.

So, either I installed the diode incorrectly, or my old 12V source for the fan trigger was switched, and I'd forgotten that. Seeing as the 12V source for the trigger was tied into the main fan power feed, I don't think that was the case.

I'm guessing that your fan relay is connected to the battery voltage directly, no switches or relays in the path, and that your fan diode is now connected to MS +12v, after the main MS Relay board relay.

If so, what's happening is that you're back-feeding MS +12v from the battery, through the fan relay coil (~100 ohms), through the diode to the middle of the relay board. The ~100 ohms of the relay coil drops too much voltage to provide full power to everything, but is enough to give partial voltage and weird behavior. The relay board includes a couple polyfuses which may be tripping and causing the no start. If you pull power, the polyfuses cool down and re-connect.

You can either move the diode back to the relay +12v, or move the relay coil +12v to +12v after either the Main relay or after the Fuel Pump relay.

Yeah, thanks for the confirmation. I had just been sitting here looking at things and realized that's exactly what happened. The diode is connected to the MS +12V now.

The easiest thing to do is probably move the diode back out to the relay +12V (and not try and fish another wire into the cabin to connect to the MS+12V).

Thanks!

Relocated the fan diode back out to the relay. Everything is good to go now.