Fuel pressure in TBI conversion

[IronDog]

I've got a 1990 vintage GM TBI conversion on my '91 GW, with the electric fuel pump mounted on the frame rail in the engine compartment. It's been working fine for nearly 40K miles. I recently hooked up a fuel pressure gauge - between the pump and the TB - and noticed that most of the time, the fuel system doesn't hold pressure when it is shut down. But a couple of times it did hold the pressure and I noticed how much quicker it started when it didn't have to wait even a couple of seconds for the fuel pressure to build up. That got me thinking whether it should be holding pressure or not. Don't most fuel injection systems hold the fuel pressure when the engine is shut down? Should the GM TB hold pressure? Seems to me it would just bleed off into the return line, but something made it hold at least a couple of times. Maybe the return line was clogged or something those times. Does anyone know how it's really supposed to work?

[AMX factor]

Pressure should be in the 15psi area. I know you've gotten lots of miles already but you are supposed to mount the electric fuel pump as close to the fuel tank, if not in it. The longer distance moght be a factor in it not holding pressure, also might have a hole in a line somewhere.

[Serious Johnson]

I know that the higher-pressure port injection systems hold pressure -- gotta bleed it off before cracking open any fuel lines. I assumed that they all did, but the GM TBI on my Jeep (w/ new injectors & in-tank GM pump) doesn't seem to hold pressure either (haven't yet gauged it). It generally takes 5-8 seconds to light off, which ain't no great hardship, but my other carbureted Jeep fires more quickly.

Sorry I don't have the answer -- guess I'm just hanging out on your thread and waiting on a more learned response.

SJ

[ November 09, 2004, 01:00 PM: Message edited by: Serious Johnson ]