09-29-2011, 04:41 PM
Join Date: Jun 2011
Total Cats: 0
Today thought about the MX5 quite a bit and got straight on to trying to confirm the grounding problem when I got home:
Put fuel relay modified wire back to a body ground (except extended it into the engine bay so I could hear the injectors).
1 Pulled the injector relay (car off) and injectors would not run (car on), put back in and they opened = this relay works fine.
2 Turned car to on position = fuel pump on and injectors open. I then removed the fuel relay wire from body ground = fuel pump off and injectors off!!
3 Put fuel relay wire to body ground and started car = car runs fine. I then removed the fuel relay wire from body ground = fuel pump off and injectors off. Now this was hard to hear the injectors on with the car running, so I got my car stethoscope so I could hear the fuel running through the injectors and did it again. I removed the fuel relay wire from body ground = fuel pump off (but there is enough fuel pressure at the rail to be able to supply the injectors for a few seconds) and the injectors turned off!!!!!!!!!!!
Therefore as really weird as it might seem, I am 110% sure that the fuel relay being on a permanent body ground is also causing the injectors to see a permanent ground = they are open.
I still believe the car has always done this as it is only possible to hear the injectors if your head is under the bonnet, you can't hear them in the car even with the bonnet up and windows down. The fuel pump is also quite quiet inside the car even with the tank inspection cover off and carpet lifted so I could get to the wires, you can hear it standing outside the drivers side. So I would not have noticed this in the past.
I know it does not make much sense but I am sure this problem is due to the ECU's fuel pump circuit having the component burnt out. This component is controlled by two or three other large components on the board, so the ECU must control the grounding of the fuel pump relay. Otherwise the fuel relay would have been grounded to the body at the factory.
Unfortunately I don't have the experience to work out exactly what this OEM ECU circuit is doing or even think I can work out what the components are!
The only thing I could do is cut the Emanage out of the wiring loom, put it back to standard again and see if the problem is still there. This would be a major pain in the *** though and would take a good couple of hours to do and re connect the EManage by soldering the wires (I'm not too keen on the idea of bullet type connectors for this).
I wonder if there is anyone local (Dorset, U.K.) who could lend an OEM ECU for a quick test?