Yes at this point I'd replace ECU, since he's already been through 2 main relays. Bad ECU's are rare so you really want to rule out other stuff first.

 

Replacing the ECU is worth a shot, but it's unclear that the main relay gets battery voltage from fuses 31, 24, and 18 and that it delivers this voltage to the ECU, and that the ECU is properly grounded by G101.

 

If it were a blown fuse, the car would never ever start. But the ground wires are certainly possible.

During this 20 minutes waiting for the ECU to boot up and the pump to prime, you could wiggle and bang on stuff to see if anything is loose.

 

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How would I check G101?

 

Do you have or can you borrow or buy ($10-$25) a digital multimeter?

 

Unscrew the bolt, check that the wires are OK and the terminal and the housing surface are not corroded, reattach and make sure the bolt is tight.

 

Some light sanding of the contact points of the ground wire and thermostat housing might also be a good idea.

One test I was recommending was to ensure low resistance between body ground and the ECU terminal that runs to G101.

 

I do. Its a Fluke 110 True RMS Multimeter I borrowed from my dad.

Its good there, had a bit of general engine grime on it, cleaned it off, didn't make a difference (I wasn't expecting to anyway).

 

Where is said ECU terminal. Its should be less than 1 Ohm right?