Thread: EFI earths

Mostly at the back of the LH cylinder head, one 10mm ring tab under a short 3/8" UNC bolt. Usually loose and dirty, I transfer it to an inlet manifold bolt where it can be seen and checked occasionally.

Originally Posted by bee utey

Mostly at the back of the LH cylinder head, one 10mm ring tab under a short 3/8" UNC bolt. Usually loose and dirty, I transfer it to an inlet manifold bolt where it can be seen and checked occasionally.

And where does the earth strap bolt to on the body? Currently it's attached to the AFM mount, but I remember it being somewhere else on another vehicle I have worked on..

Originally Posted by Konradical

And where does the earth strap bolt to on the body? Currently it's attached to the AFM mount, but I remember it being somewhere else on another vehicle I have worked on..

Not 100% sure (I no longer have a 3.5 EFI) but any earth over there should be bolted to the ignition coil bracket together with a braided strap from the engine.

Originally Posted by bee utey

Not 100% sure (I no longer have a 3.5 EFI) but any earth over there should be bolted to the ignition coil bracket together with a braided strap from the engine.

Ok awesome thanks.

There is a braided strap between the coil and engine.

I kinda remember it being attached to the firewall somewhere, difficult to get to, but will clean as is and hopefully get a result.

Originally Posted by Konradical

Ok awesome thanks.

There is a braided strap between the coil and engine.

I kinda remember it being attached to the firewall somewhere, difficult to get to, but will clean as is and hopefully get a result.

You might be thinking about the rack of relays under the cover behind the washer bottle, they don't have anything to do with the EFI though. Main EFI relay and fuel pump relays are next to the ECU under the seat complete with fuses. The only thing I can't be sure of is where exactly the ignition supply for the ECU comes from, there may be a relay involved. Good luck finding that. With your ignition switch on check at the plug between the EFI loom and the body loom (by your left little toe as you sit in the drivers seat) for 12V at a white wire or white/green wire, key dependent. This wire is not a high current source and can be hot wired directly from the ignition switch.

Yeah, I just remember the strap being attached somewhere around that area.

The power for the ECU comes from that EFI relay under the seat, origin of power I'm not sure. I have it, I know that, but from tracing the rave diagrams, it seems to come from the instruments.. not really sure..

Originally Posted by Konradical

Yeah, I just remember the strap being attached somewhere around that area.

The power for the ECU comes from that EFI relay under the seat, origin of power I'm not sure. I have it, I know that, but from tracing the rave diagrams, it seems to come from the instruments.. not really sure..

ECU power comes from live battery feed on a fattish plain brown wire, through the aforesaid plug by your toe, the origin of which is probably the brass bolt through the firewall under the brake booster. There is a whole bunch of these brown wires that take unfused power to all of the relays scattered about the vehicle. This bolt is worth cleaning and tightening as it also carries the starter motor power cable on the engine bay side. The lack of fuses on all of these high current wires is truly a Lucas engineered wonderland.

Makes sense..

I did have that power stud apart when I had the dash and front carpets out (well I kinda still do, considering my "replacements" don't fit properly). I know that it is tight and getting good power. Am surprised to know it's not fused though.

Randomly, have you ever had the taco needle jump with the key in the on position, engine not running?