Occasional no-start, turns off while cruising

[whitebulat22]

I'm mostly sure I should but I've been wrong about diagnosing a lot of things. The car will occasionally not start for about 10-20 minutes, turn off in completely random low or high gear cruising states (sometimes not to be restarted after), and neither of my 2 early style eta fuel pumps are making any priming or clicking noises when setting the key to the on position. Car is usually significantly nastier about being lugged and stumbling at low revs than other etas.

Fuel pressure was read to be low a year ago, it was a AAA approved shop and they recommended getting one but they were also free because my car wasn't fixed after their service.

Tips on anything to check / where to measure voltage readings for the pump, or a "just do it" greatly appreciated.

[whitebulat22]

Update: Car is running like factory now with other maintenance, but will still randomly turn off in any gear at any speed and display 0, or occasionally erratic RPMs on the gauge. It will usually restart by key but not bump start. Because the cluster gets the RPM signal from the ECU I am assuming it must be either something that powers / grounds the ECU or sends the RPM signal to it. So according to Motronic 1.0 diagram I should check all of the wires that say ground or crank sensor on them, and the main relay. Probably just the main relay / crank sensors because wires themselves would probably not jump out of contact over smooth surfaces when it dies.

Am I on the right track?

[ak-]

Check the oil pan ground.

[StereoInstaller1]

Main relay

[whitebulat22]

Ended up being the ecu. Although i got a fixed coolant gauge when the ground was tightened and now carry a spare main relay.

I have 3 broken 027 ecus now. One has a mark d chip id dearly like to use in my working one but 2 of the 3 others are broken after chipping attempts. Are they usually so delicate? And would anybody take them for free or are they trash?