I have a 96 k1500 4x4 with the 5.7L Vortec motor.
At freeway speeds I was recieving a p0300 code which would go away when driving in town. I could feel the slight misfires while in cruise but it ran strong under load and acceleration.
Most recently the fuel was low and I stopped to get gas after the fill up I got back on the freeway. The truck got up to freeway speeds and then began to misfire very badly to the point I had to pull off the road once at idle the truck promptly died. Now its parked at my house and it starts just fine goes into high idle then levels out for a few seconds when the rpms drop as does the fuel pressure to 45ish (checked with gauge) the engine
begins to sputter and then the fuel pressure goes back up to roughly 60 and it recovers. It goes through this cycle 3-4 times each time it has a harder time recovering until it dies out. If I give it gas the misfires start up again and the motor shakes hard enough to rattle the exhaust
I hooked up a fuel pressure gauge and with key on/engine off I get a fuel pressure of roughly 60psi. When it runs that drops down to roughly 54psi until it starts to do its dying thing. When I rev the engine it seems to hold around 59psi.
What I have tried so far: Cap and rotor, plugs, wires, EGR valve, fuel filter, CPFI ot MPFI conversion, I checked the distibutor gear it looks good but I havent checked it since the new symptoms started, coil pack, checked what I could on the vacum lines and intake manifold for leaks but I dont have the propper tools for that.
Any thoughts? I am not quite sure where to go from here.