Having problems with my mates car.

Basically the ECU relay won't switch with the ignition. I've ignition 12v to one side and the other side is connected to pin 10 on his L8.

However if i disconnect this pin 10 and earth the side of the relay, the car runs fine.

It used to run with pin 10 connected, which is the puzzling thing?

Anyone any ideas?

 

Have you changed the chip recently ?

 

Nope, The ECU is actually on my mates RS turbo.

The engine was rebuilt over the winter and the dash changed, the ECU wasn't touched internally.

Its this pin 10 that gets me. On the wiring diagram i looked at, it shows 12v to both sides of the coil? Thats whats confusing me? It works fine if one side of the coil is earthed? However the wiring hasn't changed so it muust have worked like this before hand?

 

pin 10 is the 0v side of the ECU relay coil.
Do you have power to pin 20 when pin 10 is connected? have you changed any relays recently? it sounds like the relay is normally closed instead of normally open?

 

Haven't checked pin 20 yet, but i know pin 10 wasn't an earth, i had +12V at it?

No relays changed, only thing i can think is something has been upset with the dash change?

 

on the ecu side or wiring?

 

The 12v is coming from the wiring. If i disconnect the wiring from pin 20 and run a seperate earth the the ECU power relay, the relay works and the engine runs, but they is no V at pin 10. With everything connected up like it was pre us messing with it we get 12V at the ECU on pin 10.

I thought pin 10 was supposed to act as the earth to trigger the coil?

 

nope, the coil earths to the ignition amp, which is connected to +12v and pins 24/25.
i would try a new relay i think, but it does sound very odd.
have you tried pulling the relay out and checking what you have got to either side of the coil and then checking with the relay plugged in?

 

Sorry by "I thought pin 10 was supposed to act as the earth to trigger the coil?" i meant to trigger the coil on the relay. Its a bit confusing the way i worded that lol

I've tried another relay and its still the same.

So am i correct in saying that pin 10 provides the earth that enables the ECU power relay to activeate with the ignition live?

Think we are going to have to measure the like of my Sapphire to see what way its working and compare it to the RS turbo.

 

Your correct about pin 10 being the earth/ground of the coil side of the ECU relay . The +12v supply to the coil side of the ECU relay is shared it seems (L8 diagram) with the the +12v supply to the ECU .It will need a positive 12 volts to activate it is my understanding .

 

It's a bit like a fuel pump relay output. For safety/security.

Unless the ecu is in place, or possibly detects a crank signal, it will not energise and allow fuel to be pumped.
So the ecu controls this, and will ground the relay to allow full operation. If you test this output with a voltmeter and get 12v, that is perfectly normal in it's safe state. Rather than having no earth connection. They simply apply 12v to the coil instead. 12v to both sides = no potential difference so the relay will never energise.

 

With the ECU in place and when cranking over, it still doesn't work. It wont even prime the pump on the second ignition position like it normally should, however if i add my own earth everything works fine?

I'm beginning to wonder if its an ECU fault?

 

Sounds possible.