1984 240 wagon will not start
Bought at 155k now with 247k miles; tank pump replaced within last 30k, main fuel pump and regulator not since I bought it. Fuel filter in last 40k or so.

This seems to be a puzzler.
Every so often will start, so timing, fuel injectors, coils and fuel system all seem to work, at least then.

Tested fuel system pressure, around 37-38 psi at rail, with fuel pressure regulator in circuit. This is with just both pumps on, jumpered from fuse position 7 to 5, to bring them up and on. I can hear fuel bypassing in the regulator.

There are times after the car has sat for a day or so, I click the starter and it fires right up. This happens at night, so I don’t think its related to pressure in fuel system building up higher due to daytime temps. When this occurs, it fires just like the car should and runs fine. If I turn it off then try to start it, it will simply crank and crank.

I thought that perhaps when cranking, not enough fuel pressure was getting to rail, due to lowered voltage while cranking. As a test, I kept the battery full up, jumpered the pumps on as listed above, thinking that a little more voltage to the pump might be the trick. It was not.

My only though is that the car, when running has approx 13.5 volts on the system perhaps driving the volume and pressure up in the Fuel Inj system, when the battery charger does not go quite that high.

Is the fuel pressure high enough, my guess is yes, because I can hear fuel bypassing in the regulator with the engine off.

I have thought about changing the main fuel pump, but would not want to do this unless pretty sure this is the problem. Perhaps theres a problem somewhere else obvious I have not considered.

Any ideas- I'm really puzzled.