First---89 YJ with 93 HO 4.0---Jeep runs great once started.
I've had this problem since I bought my jeep and thought it was time to fix. I have to prime the pump 2 cycles and then shortly turn the motor once and back off then it will start. The pump will only cycle approx .5 seconds before stopping. I checked the fuel pressure and all was good while running but as soon as the key goes to off, it drops immediately to zero. Changed the fuel press regulator but no fix. Thought the check valve in the fuel pump was probably bad. Dropped the tank and changed the pump. Still drops to zero immediately and the prime cycle is still about a half a second.
Ive read on hear that a pressure drain over a couple minutes is a leaking injector but mine is instant.
Why is the prime cycle so short and why does my fuel pressure drop so fast? There are no leaks between the pump and the fuel rail.