My van is 6cyl, 4.9L, auotmatic transmission. There is no knocking, no oil burning, no sign of smoking. It starts fine, sounds and drives fine until oil pressure starts to drop. When pressure is completely gone the engine stumbles and temp gauge starts going up. Does this van have an oil sensor? and if so, where is it?
Look near the oil filter for the sensor. You sound like it’s a legit pressure issue, but I was of the impression that Ford did away with legit gauges over a decade ago. It’s a glorified idiot like via needle. It wouldn’t read anything below some really low pressure and shouldn’t vary much at all in any NORMAL sense.
How long does it typically take for this event to occur from cold start? This will somewhat gauge at what viscosity you’re getting into trouble.
Since you’re not showing any of the usual suspects that would account for a wear related origin for this, AND you don’t seem to indicate a slowly progressive issue with lifter noise and whatnot with an advancing level of frequency and severity, I think some scoring/seizing/fouling of the pump relief valve may have occurred. This would be invisible at cold start, yet allow below acceptable pressure as the oil warmed.
This is the Ford Truck block that evolved from the 240 of yesteryear. Very durable and serviceable engine. I’d have the pan pulled and the pump changed. If that’s not possible ($$$), I’d up the visc about two ticks and see if you can manage a stable full time pressure situation. Then I’d debate on trying some solvent engine flushes to see if that remedies the situation. I’d prefer something like Auto-Rx, but you may not be able to manage enough normal driving at temp to allow it to work.
Good luck. You’ll have a few people telling you to verify the pressure with a mechanical gauge, and while I don’t find that a bad thing, you do show REAL symptoms of low pressure and you’re just paying Captain Obvious to confirm it. Often times this is the first advice when there are absolutely NO symptoms …and the cost of changing out the sensor is CHEAPER …yet it has become routine rhetorical advice as though everyone has a thick wallet.
Geezers (I’m one) tend to get so cautious as we age that we’ll tell you to install Titanium shielding on the roof just in case there’s a stray meteor shower. “If you don’t do it, you might get struck”. 