Weird engine cut off issue at speed - seeking ancient wisdom
 

Got a new 7.5 460 carb engine in an '84 Ford e350. Runs and idles great. After 200 break in miles it gets to 60-70 mph with no issues and drives well for 15-20 min, then two things appear to happen.

The oil pressure slowly drops (oil is right level of 10w-30 per stick) and the engine seems to stop (like I turned off the key in neutral). I test bypassed the low oil pressure cut off switch and could read pressure via the oil pressure sender to the gauge. It was normal pressure at cutoff.

Temp is normal range about 10-15 degrees hotter than the new thermostat and outside was 85F. Alternator and voltage regulator is new. Vacuum lines, Carb, Gas lines from carb to pump thru filter to tank is new. Fuel filter is clear. Fuel is new. Fuel selector works. Fuel pressure is 6-8 psi (not fuel injected) at carb. Fuel flow is consistent. Carb idles and 2500 RPM in driveway fine for as long as I have it set.

When it dies, I go to neutral and restart it. 5 times this happened in 1.5 hrs freeway driving. Oil level checked 2 times. No smoke at engine or exhaust. However, 2 of these times it backfired before I could start it at about 40 mph but engine off and coasting in neutral. Presumed that was the choke closing or ???

Oil pressure sender is new. Oil pressure cut off was tested in a bypass mode, same engine "off" happened. Wiring harness in engine bay was replaced and checked. No computer just an ignition box. Only old parts in the entire chassis is the valve covers, oil pan, C6 trans and electric pump in the tank. Engine also has a mechanical pump per rv specs (no idea why rv's called for elec in tank and a mechanical as well. I have tested with and without the mechanical pump in the loop though. Electric pump and mechanical output the right psi (6-8 psi) and flow. No loss of power up hills, drives great otherwise. No hiccups, hesitation etc in the pedal. Timing is 8 degrees BTDC as per spec with dist vacuum plugged and disconnected around 850 rpm. No known vacuum leaks as all lines were replaced.

What the hell else can I check? Bad key switch under the dash? When it dies, all the gauges still work and it's as if the key were turned off with exception the gauges work on the dash. It's very very odd.

460's in vans were known to vapor lock. At some point there was a T in the fuel line at the carb that has a orifice valve to prevent that. They would just kinda shut down.
If it had the old fender mounted Ignition module, I have had that happen when not using Motorcraft spark plugs!
That is 2 possible causes. Loss of electrical power to the Ign Module, fuel pump it electric or some ground wire issue.

You may post your problem in the forum for 460's, RV section, Fuel, Electrical and Van section if you haven't already. Some one there will be along to help soon I am sure!.