'89 Stalls after warmed up

[T-Moto]

Hi guys, stumbled across this forum looking for some information and it appears to be pretty helpful, so here goes.

My son just acquired a 1989 Olds 98 Regency with approx. 197,000 miles on the 3.8 V6 which had been sitting for years before he got it about two weeks ago. When cold, it starts right up and runs pretty well, sometimes for ten miles or so before it starts to stumble and what I will call bucking. The more the accelerator pedal is pressed, the worse the bucking will get, like it will rev up and go, then hesitate and stumble, then rev up and go, them stumble, etc., until eventually it will die. It will start right back up, and idle pretty well for a few minutes before it will eventually die out again, but attempting to drive it results in this bucking behavior. The temp gauge does not indicate it is overheating either.

While looking into what the problem could be, I hooked up a fuel pressure gauge to the valve on the fuel rail and got about 12 psi with the key on but not starting the car yet. After starting the car, the pressure goes up to about 30 psi and after idling for a few minutes the pressure slowly drops, and it starts to stumble at about 15-20 psi and eventually dies when the pressure drops to zero.

I'm thinking that since the car dies after the pressure drops, it appears to be the fuel pump or something related? Which to me may explain the bucking like it's getting fuel starved. What I don't understand is that once the car cools off, usually the next day or so, it runs fine for ten miles or so, until these symptoms appear. Any help is appreciated.

Edit to add: Also wanted to mention that the check engine light does not light up, indicating any trouble codes, which is what led me to believe it was some sort of mechanical issue and not electrical/electronic in nature.

[vengence1979]

I got Am 88 regency braumham doing the same thing but mine gives code 42 bypass mode? I/m 99.9 its the knock sensor. Pretty sure...anyone?