lq4 swap won't run for more then a few seconds

[Silverado889]

hey guys, I have a 70 c10 I just put an lq4 in. it has a cam, long tubes, and typical supporting mods. I'm running an aeromotive fuel pump and bypass regulator into FAST fuel rails. the PCM has been tuned by Nelson. the problem is, it starts, but dies after 2 or 3 seconds. I was hoping someone could help diagnose this or point me in a direction. thanks in advance

[Frenchy]

Dratically losing fuel pressure, or VATS

[farmtruc]

check fuel pressure, unless it's a corrupt pcm, it def won't be vats, we turn that off for sure.
pm your name and info, we'll compare notes.

btw, fuel pressure should be 55psi or so. what did you set it for?

[Silverado889]

Nelson tuned it and they knew it was a swap, but maybe they didn't eliminate vats? and as far as I can tell, the regulator stays strong at 58 psi. but, as soon as the pump shuts off, pressure drops immediately. should this happen?

[jansen]

Fuel pressure regulator?

[Silverado889]

regulator is an aeromotive bypass regulator, set at 58 psi. this is a new swap, and hasn't run yet, so could there be other possibilities also?

[RedHeartbeat]

blew a hole or have a leak in the fuel line between the pump and the tank metal fitting.

[Wagonbacker9]

Nelson tuned it and they knew it was a swap, but maybe they didn't eliminate vats? and as far as I can tell, the regulator stays strong at 58 psi. but, as soon as the pump shuts off, pressure drops immediately. should this happen?

The pump shouldn't be shutting off... but yes, the pump shutting off should definitely result in a loss of fuel pressure...

[RedHeartbeat]

put a one-way check valve between the pump and the fuel rail to hold the pressure if it's bleeding back through the pump. How do you have your fuel lines plumbed? Pump to rails, rails to regulator and then bottom port of the regulator back to the fuel tank?

[pl4yboy]

The pump shouldn't be shutting off... but yes, the pump shutting off should definitely result in a loss of fuel pressure...

Actually, shutting the pump off should result in a loss of fuel pressure over an extended period of time... not instantly by any means. My truck will still be holding 50+ psi after 5 minutes of the truck being off.