Engine runs with key off - MSD ignition related

[patrickbrown]

Hey All,

I just moved the switched 12V wire of my MSD 6AL box to my relay panel. Just to be clear - prior to this everything was working just fine. I have a row of seven Tyco/Bosch relays in a custom relay panel. I've been working on tidying up my under hood wiring and moved the MSD box to the dedicated ignition (IGN) relay. Since then, the car engine starts great but will not stop when the key is turned off. If the key is put in the run position it will energize the IGN relay. When the key is off it turns off - no voltage on the output. If the car is actually started, it will keep the relay energized when the key is off. This must be back feeding the main relay as well because the injectors and computer keep working. There is a fuse inline between the IGN relay and the MSD box. I can pull the fuse to stop the car.

Any ideas how to fix this? I'm thinking this will involve a diode somehow.

[patrickbrown]

I stopped at Radio Shack on my way home from work. I now have a IN4001 diode. I wired it across the coil of the IGN relay which is also in parallel with the EFI relay. The stripe on the relay was connected toward the +12V side. It didn't help.

I'm thinking about changing the trigger side of the IGN relay to be powered by the load side of the EFI relay (Main relay). Do you think this might help?

[DonTZ125]

Could you post a wiring diagram / sketch? I'm having a bit of a time wrapping my brain around what you have here...

[jb007]

HI. I had a very similar problem. Your right about using a diode, the solution was to put a diode in series with the ignition warning light output from the alternator. Back EMF (voltage) was keeping the Megasquirt alive. Hope this fixes your problem.

[patrickbrown]

Well I was trying to sort this out this evening with no luck. I'm working on a diagram to post. But in the meantime, you can just refer to the standard V3 MS2 diagram from MegaManual. I followed it exactly. The differences are that where you see the yellow wire from the switch to pin 86 on the main and fuel relay, I have four. My relays are MAIN, IGN, AUX, and FUEL. Pin 86 on all four of these is connected to each other and then to the ignition switch. This has been working until I moved the MSD unit to the IGN relay.

I was also reading the MSD ignition manual. They state that I could place a small resister inline to the small red wire. They don't define what value resister. I may try a few resistors and see what happens.

[jb007]

HI. I had a very similar problem. Your right about using a diode, the solution was to put a diode in series with the ignition warning light output from the alternator. Back EMF (voltage) was keeping the Megasquirt alive. Hope this fixes your problem.

This thread mentions this problem: http://www.turbominis.co.uk/forums/inde ... tid=302401

[trakkies]

I stopped at Radio Shack on my way home from work. I now have a IN4001 diode. I wired it across the coil of the IGN relay which is also in parallel with the EFI relay. The stripe on the relay was connected toward the +12V side. It didn't help.

I'm thinking about changing the trigger side of the IGN relay to be powered by the load side of the EFI relay (Main relay). Do you think this might help?

A diode across the coil is to kill the back EMF when the relay opens - usually to prevent damage to a driver transistor, etc. If you need to isolate two feeds to the same device, fit one in series with the coil. It is wired opposite polarity to a snubber one - stripe goes to negative.

But why are the ign and pump relays in parallel?

[patrickbrown]

I was fiddling with this this morning. I found the cause but haven't fixed it yet. I have a one wire Powermaster alternator. This car came originally with a 30A generator. This new alternator has the charge wire going straight to the battery. There is a second optional connection for the gen/alt warning light. I unhooked that wire and the engine will start and stop reliably. So it does seem that I need to add a diode to this circuit. I'll work on getting that in place this evening.

So why should I not have my pump and ignition relay in parallel? The pump relay is in the trunk with the battery. The ignition relay is up front with all the other relays. I was told that I should have a separate relay for the ignition because my EDIS8 (not installed yet) draws a lot of juice.

[trakkies]

I was fiddling with this this morning. I found the cause but haven't fixed it yet. I have a one wire Powermaster alternator. This car came originally with a 30A generator. This new alternator has the charge wire going straight to the battery. There is a second optional connection for the gen/alt warning light. I unhooked that wire and the engine will start and stop reliably. So it does seem that I need to add a diode to this circuit. I'll work on getting that in place this evening.

So why should I not have my pump and ignition relay in parallel? The pump relay is in the trunk with the battery. The ignition relay is up front with all the other relays. I was told that I should have a separate relay for the ignition because my EDIS8 (not installed yet) draws a lot of juice.

The pump relay is controlled by the MS for two reasons. It won't run with no tach signal to prevent flooding and possible hydraulic lock if an injector is leaking. It also cuts off the fuel supply in event of an accident which stops the engine.

[patrickbrown]

I was fiddling with this this morning. I found the cause but haven't fixed it yet. I have a one wire Powermaster alternator. This car came originally with a 30A generator. This new alternator has the charge wire going straight to the battery. There is a second optional connection for the gen/alt warning light. I unhooked that wire and the engine will start and stop reliably. So it does seem that I need to add a diode to this circuit. I'll work on getting that in place this evening.

So why should I not have my pump and ignition relay in parallel? The pump relay is in the trunk with the battery. The ignition relay is up front with all the other relays. I was told that I should have a separate relay for the ignition because my EDIS8 (not installed yet) draws a lot of juice.

The pump relay is controlled by the MS for two reasons. It won't run with no tach signal to prevent flooding and possible hydraulic lock if an injector is leaking. It also cuts off the fuel supply in event of an accident which stops the engine.

I understand that. My pump relay has the ground pin 85 going to MS. Pin 85 for the MAIN and IGN relays both ground at the engine block. Clearly the car would never start if the IGN pin 85 was connected where the pump one was unless lucky and it happened to start during the prime pulse. Not likely.

When I say that my pump and ignition relay are in parallel, I am talking only of the +12V side.

[trakkies]

[snip]
When I say that my pump and ignition relay are in parallel, I am talking only of the +12V side.

Ah - just a terminology problem. ;-)

[patrickbrown]

I tested the diode fix. It works. I placed the diode inline with the wire to the dash warning light at the alternator. This is a temporary fix until I get time to open the dash and move it to there.