Review: no fuel pfress change; parts seem ok

[WhalePirot]

no fuel press change; parts seem ok

Odd issue, here, which may be a sticky diaphragm in the FPR (non-adjustable).

-Fuel pressure w/ vacuum hose pulled is proper; that vacuum reads 22psi; about right.
-Using a hand vac pump attached to the FPR, it holds vac pressure perfectly, but but minimal FP drop.
-The FPR is stock and nearly new (doesn't mean it's good).
-The engine idle changes a small amount when reconnecting the vac line, and the FP drops 1-2 #s. Too little, I think.

The drive symptoms are a lack of power, say at 60mph, when accelerating and there is a whining noise, kinda like a vacuum leak. The car idles and drives great otherwise. It may run slightly rich, which is proper IF the FP is not regulated at high vacuum.

The FPR feed hose is new vacuum line and has no fuel in it, nor is there any fuel smell.
It seems either the pressure gauge is wrong, or the FPR sticks and does not regulate pressure properly.

thoughts?

 

[Hib Halverson]

What is the fuel pressure when tested per the Service Manual, ie: key on engine off?

Does it hold when the key is turned off?

What is the fuel pressure with the engine idling?

 

[WhalePirot]

changed pressure regulator.. no change.

FP drops very, very slowly until it zeroes, so I think the gauge is fine.

FP=39 at all times/loads/RPM.

Car fires up immediately upon start.

Perhaps the return line is restricted or blocked, somehow.

 

[Hib Halverson]

In re pressure drop: if by "very slowly" to zeo you mean 60 minutes, you're likely ok. If you mean one minute, there's a problem. In my experience, if the fuel system is in good condition, I can pressurize it then come back in six hours and see the pressure has still not gone to zero.

Also, the pressure when the engine is running under load is secondary to what it is key on, engine off then key off. That is, fuel pressure, first, must pass the test in the FSM. Once you pass that if you still have symptoms of lack of fuel, then you need to look at what the pressure is doing with the engine idling and, later, under load.

Because the pressure dropping is a bit subjective as a symptom, it's hard to make a judegement over the Internet, however, I think I'd start looking at problems which can cause a pressure drop.

As you suggested before, a bad FPR could do it.
defective check ball in the pump can do it
Leaking injectors can do it

 

[WhalePirot]

The pressure drops about 1 psi/5 minutes, so there is likely some small leakage at the injectors.

With or without vacuum applied to the FPR, the FP is 40. It varies not at all with vacuum applied, wich is not right. The running FP may not be primary but it should vary with vacuum; the whole purpose of the FPR. That would point, perhaps to a restriction in the return line.

I removed the FPR and blew compressed air through the entire length, i.e., from the hole in the manifold where the regulator passes return fuel. I heard the air gurgling in the gasoline tank.

I'd checked the voltage at the pump, which was only 6.5vdc or so. The pump runs fine at that or 12vdc, straight from B+. This came in handy when a post blow-out-return-line held no improvement. I drove the car with jumpered 12vdc to the pump, and it still stumbled on acceleration.

I checked most of the intake with propane, for vacuum leaks: no variance in idle. This, for the partial throttle 'whistle'. The MAP is about a year old.

Next, I guess, is the fuel filter, also rather new, but I am concerned about not showing FP at key-ON, despite the car's immediate starts. I'd expect longer cranking before firing, with no startup FP. Perhaps the filter is fouled, which might explain 40 versus 45 psi not-running FP. Maybe I am talking myself into another part, but this issue has been progressive, which debris in a project car's tank would cause.

That's about all in the system.

 

[WhalePirot]

Solved

I removed the brass element from the aftermarket inline fuel feed, cleaned it, but did not reinstall the element before a drive.

Holy carp! The car lit up and kept revving to the AT shift points! While the FP rose maybe 2psi (none at key on), but an immediate start. I guess this brass filter is not ok for EFI.

Time for y'all to shoot me, tho. This engine is neither Chevy nor in any bowtie; rather a 5.0L EFI blue oval in our '55 Nash Rambler. The SEFI system design, pressures and operation is nearly identical to C4s, tho. Everyone calls this totally stock looking car a sleeper, but a grin spreads when they see and/or hear the dual exhaust. 300+hp, in a car shipped with 50, is fun despite the 2.73 gears, AT and A/C.

Thanks Hib, for the thoughts and help. You'd get a kick out of this wife's daily driver, I believe.