luftpirate

Yes it's unfortunate in that respect, about 80% of the community does know exactly where I live.

Bri Bro

The power to the ignition coil comes directly from the ignition switch, no fuse or relays in the path. I am betting you toasted the ignition switch contacts. THe DME gets power through the DME relay but the ignition drivers in the DME only ground the other side of the coil. I am guessing the short was from the power lead to the MSD unit to ground which would cook the ignition switch.

luftpirate

This one has me stumped.

Started with battery unplugged and DME Relay out.

1) Plugged in DME Relay and battery. Put Volt meter on +/- on coil. Nothing
2) Put Key in, tried both off/acc. postion. Put Volt meter on +/- on coil. Nothing
3) Started car, Put Volt meter on +/- on coil. ~4 to 1v (Guessing its pulse, not contant)
4) Turned key off, car still running, still get ~4 to 1v
5) Pulled key out, car still running, still ~4 to 1v
6) Pulled DME Relay, Car shuts off, Put Volt meter on +/- on coil. Nothing

So is it still possible that its the switch which is damaged and something is continuing to jump once current starts passing through it, but only after its been initiated?

Okay so the coil green wire (-) goes directly to the ignition switch? I saw on a diagram where it also goes to the factory alarm, I unplugged the alarm thinking maybe a diode had blown and current was back feeding that way, but no luck there either.

I was under the impression that the black wire goes to to the ECU because that is the (+) which we are supposed to put the ballast resistor on to protect the ECU w/ MSD coil. But if not then is everyone wiring their resistors on the wrong wire because normally on most cars (+) should go to the ECU and not (-) ??

peanut

the ECU controls everything in the ignition and fuel delivery system, including your coil
Everything is grounded through the ECU (not chassis ground)

Something seems to be supplying 12v+ to your DME relay coil with the ignition off. There must be a short somewhere ?

With your ignition off there is 12v+ at terminal 30 of your DME relay socket. This is one side of the DME relay coil.

When your ignition is turned on the ECU grounds the other side of the DME relay completing the circuit. This energises the relay which in turn switches two seperate circuits through the relay. One to the fuel injectors and the other to the fuel pump

At this point there is no voltage going through the coil because the engine is not turning . The pump has pumped fuel for 1 second only and the ECU has swithed it off.

Only when you crank the engine and the ECU 'sees' 200+ rpm from your crank sensor will the coil be energised and the ECU pulses both your injectors and the coil.

If any of your temperature , 02, air temp ,or crank sensors etc are faulty the ECU shuts it all down to prevent a fire in the event of an accident.

Something in your car is over-riding the DME relay keeping it energised with the ignition off .

I'm leaning towards a faulty ignition switch. Can you substitute another ignition switch ?

luftpirate

Ordering a switch now, Im hoping that will be the simple fix. Thanks

peanut

ouch they're kinda expensive arn't they ? Have you not got access to a used one you can borrow? A new one will mean two keys to the car I guess ?

If you can pull your cables off your existing switch without removing it from the column then you could connect and try the new switch whilst its dangling loose . It might save you some work if the original switch is ok .

luftpirate

The early ones are less expensive, they range from 7 to 40 bucks (Pelican is out of the cheap ones), I'm picking one up at O'reilly tomorrow for 35 bucks (lifetime warranty - and with my luck Ill probably use that). It's just a switch which goes at the end of the lock cylinder, so no new key.

944Ross

Wouldn't jumpers simulating the connections in the ign. switch tell you right away if the switch is the problem? Any sign of high current at the plug?

Bri Bro

Check that the wires going to the switch didn't get fused together from the heat of the short. Something smoked so I hope it was only the switch contacts. The weak link in the chain should be the contacts in the switch.

Bri Bro

The green wire goes to the DME and is negative. The black is positive (I know this is the color of ground in normal cars) and goes directly to the ignition switch. Bottom left of picture is the coil, pin 15 is a Black (SW) wire that goes directly to the ignition switch. The schematic is from a 86 944T but the coil circuit is the same for the 944.

The factory alarm goes to the DME relay (turn on/off the first relay) and the alternator.

luftpirate

Ok so the saga continues,

Tonight I installed the new ignition switch. I found that insulation had melted near the switch on the larger guage black wire that runs into the back of the switch connector. There is also another black wire going into the same terminal (Im not sure what thats for)

I turned the car on, it fired up. Turned the key off and removed it. Same Old - Car stays on.
When I go to put the key back into the ignition, the car turns off.

I go turn the key over again to turn the car on . This time no start, no tach bounce. I replace the DME relay with my spare, same thing. At this point Im pissed because I feel like I now have fried something else.

I took the DME apart and checked all resistors and solder points, it looks okay.

Now this may help. I checked the two black wires coming out of the ignition switch, they are putting out 12v with the key turned on. (This is what I expected) So Ive been told one of those wires goes to the coil to power it. Im guessing its the larger guage one that has the melted insulation. I made sure it was not grounding out against anything at the switch. Connected the other end from the coil. When I stick positive lead on the end of the wire at the coil and negative to the battery terminal I get nothing. Better yet, when I stick postitive lead on the + battery terminal, and negative lead on the + coil wire which supposedly runs to the switch I get 11.5 volts. Does this mean that wire is grounding out somewhere??
I tried to trace where the coil wire physically runs in the engine bay and it seems to go inside the frame rail. I have no clue.

Bri Bro

You found your problem, you smoked the ignition coil wire to the switch and the switch itself. Switch is replaced, now time to deal with the wires. You need to run a new coil wire and make sure other wires didn't melt into a fused ball. PM me if you need more help.

luftpirate

Thanks for the help. I'm going to start with a new temporary wire just to test it, then if it works Ill have to start tearing harness apart ...

Any idea what the other black wire goes to?

Bri Bro

Black with what colored stripe?

peanut

be very careful here.

Black wires are not normally to be connected directly to chassis earth . They are invariably live 12v+ feeds that are fed to operate devices and then taken to earth through various relays ,electronic control units , sensors, etc.

it is usually only brown wires that are connected directly to chassis ground points .

The smaller 2.5 black wire coming from your ignition switch will be 12v+ and should connect directly to the coil and one of your general relays (relay G13 for example on 88 models) to feed other devices needed when the ignition is on or the engine is running.

If you try to earth the black wire with the ignition on you'll have some spectacular sparks , smoke and a cable burn .


Can you let us know the colours and relative sizes of the cables going to your ignition switch and I'll check them on the schematic