Ignition Wiring

[Joel]

Spent all day on this today, and long story short I think I've found a solution although it isn't necessarily fixing the problem...

 

The feed that supplied the wipers, heater fan and reverse light all seemed to check out, but I also found it supplied the dash warning lights (battery, oil, and brake). I removed these feeds and took the supply for them from elsewhere and hey presto it seems to work!

 

As I said, I don't really know if this is solving the problem or just skirting round it (or if I've even found the problem), but it seems to work in any case.

 

Thoughts anyone?

Edited February 4, 2012 by Joel

[Longboarder]

In practical terms when the engine is running and you switch off you are getting a backfeed into the ignition switched circuits. It may only be a small current but it is switching the relays for ecu (edis and coil) and fuel pump. They both take supplies to 30 on their relays from the constant live so once their relays are activated there is plenty current to run the engine. I suspect if you did something to drain this backfeed like switch on wipers and heater then switched off ignition the engine would stop. Going back to your Megasquirt diagram I see you have coil supply via the edis which suggests a remedy. Supply the coil terminal 2 direct from the ignition live circuit. (Incidently there is a small error in the diagram for the coil supply. You show coming from 8 and going to earth which it doesn't, as well as going to terminal 2 on the coil.)Problem solved.

I still can't put my finger on what circuit this backfeed is happening in. You suspected reverse light and now dash warning lights. Could be either. With the coil supply direct off the ignition live the problem goes away and the backfeed no longer matters.

 

Nigel

[Joel]

Nigel,

I think you've got it bang on about a small amount of backfeed switching the relays, as you say it's just finding which one. I removed all connections from the heater fan, reverse light, etc, so in theory there could be no backfeed there, but the engine still over ran. The only thing on that circuit which seemed to make any difference in the end was the dash warning lights. Incidentally, pulling on the handbrake would stop the engine, as you suggested.

 

The error with the coil supply going to earth was just a quirk of the wiring diagram I worked from, that I carried over, but I haven't actually wired it that way. Good thinking on the igniton live col supply though. I'll give it a whirl.