Okay, tried it. The pump runs if I jump 4 and 6 but still no start. I get 12 volts at the pump with the jumper on.
Then the pump works. Sounds like either the FI relay is failing OR it's not being energized

If I take the jumper off and crank the car, I'm only reading about 50 mv at the pump.
Ditto above.

I'm getting 12 volts at the relay if I remove the relay and jump relay terminals 30 and 87/2.
Not sure what you mean here. The 4 to 6 jumper takes voltage from ahead of terminal 30, and applies it after terminal 87/2. So the terminal 30 to 87/2 jumper is actually a smaller part of the same "exercise".

With the relay in, I watched it while I cranked the car and I didn't see either of the contacts move.
So you know there are 2 relays in there. One should close with Key ON (and stay closed). You should hear the "click". It powers the AMM and ECU, but NOT the pumps, injectors, etc.
A - If it doesn't click and close with Key ON, that could be the problem, because the 4—6 jumper doesn't bypass that relay, only the Fuel relay (below).

The other one is the Fuel relay, which should close when cranking. But ONLY when and IF the ECU gets an "ignition OK" signal from the Ignition CU. Therefore, it could be:
B - a bad Fuel relay, or
C - an ignition-related failure (preventing Fuel relay operation)

If A or B, you may be able to fix it by reflowing the soldered connections on the relay PC board.

I'm back to suspecting the relay but if that is the real problem why didn't it start when I bypassed it by jumping fuses 4 and 6?
Most likely an ignition problem (C), as indicated by the failure to start with pumps forced on by the 4—6 jumper, AND the failure of the Fuel relay to energize during cranking, as you saw.

I would suspect the filter if I were getting 12 volts at the pump when I crank the car.
IMO, most filters are replaced needlessly. I have never seen or heard of a (240) filter replacement fixing anything. I suppose an extremely rusty tank might clog a filter, as I have seen (once) on a 140 with a much smaller filter at the pump pickup pipe. But I'd check the flow rate before I'd change one.

You might want to start a new (ignition-related) thread, starting with your diagnosis of Fuel relay failing to "pick" while cranking AND the No-Start even with fuel pumps forced to run (the 4—6 jumper also powers injectors, and IAC, just like the Fuel relay would if it could).


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Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.