weber issues; -0- pressure after turns/driving a bit

[berettafan]

Twice now i've been out for a nice drive, say 1/2hr or so, and have had the car crap out on me. i'm not sure what's causing it but it feels like fuel starvation. the car will run very rough and die. checking the motor immediately after i see that fuel pressure has gone to -0-. leaving fuel pump on for a minute or so doesn't change this. so it seems clear that this is fuel related BUT i can hear the pump running.

Now, on both occassions after letting the car sit for about 10 minutes i turn fuel pump on and can see the fuel in the glass filters bubbling and fuel pressure returns to 3.5psi. Starts fine after that.

it did pop and buck a little on a semi-hard left turn while i was out but smoothed out shortly after. i do NOT recall this happening before the rebuild.

thoughts?

[MarkS]

I would bet the screen on the fuel feed fitting in the fuel tank is the culprit especially since you can hear the fuel pump work. Letting the car sit allows the fuel to seep past the crud fill the lines and your off again, They are a VERY fine mesh that clog up with crud/rust. A pretty sure bet on a 38 year old car. I remove the screen and install a good inline filter on the oldies.

[tfiv]

Pull out the sending unit and shine a light down in your tank. You will probably confirm Marks diagnosis.

[berettafan]

unfortunately this is not likely. just had the tank 'renu'd' which is a proprietary process that cleans tank and coats inside with, well a coating that avoids such problems. i will pull the sender just the same however.

[MarkS]

The tank may not be the issue now. Did you check the screen pickup after
removal or prior to reinstallation?

[911pcars]

I suspect the fuel pump may be gasping at life. Carefully confirm the fuel pump can output about a quart every minute and it can produce the measly 3-4 psi pressure. Are you using a fuel pressure regulator? They have been known to go belly up as well. Check pressure before and after the FPR to confirm.

Next time the engine dies, remove the air filter housing and see if you can see the accelerator pumps squirt fuel. If not, could be the float bowls are empty (fuel pump). After the engine dies, does it take awhile for the weber float bowls to refill before it starts? (fuel pump).

Sherwood

[tfiv]

If you were having problems with the tank, every part of the system is suspect, including the pump. Make sure whatever the shop put inside the tank isn't coming loose too. I've seen inside coatings cause more trouble than the rust they are supposed to encapsulate.

[berettafan]

i believe i can hear the pumps squirting after it dies.

as mentioned it takes approx. 10 minutes of sitting before i can get pressure from the fuel pump. it makes the same noise immediately after dying (and while running) but i don't see fuel getting run into the glass filters nor is there any pressure (have gauge). after sitting for a while i restart and immediately see fuel going through glass filters and immediately thereafter i get pressure.

took the car for another ride this afternoon (maybe 12 miles round trip various speeds, no hard turns) and had zero problems. avoided moderate to hard turns (ie used brakes) and it worked.

it really is a bummer having to brake for turns in a 911. hopefully someone has been down this road already....

[berettafan]

2 questions:

1-if pressure gauge shows -0- then can i assume problem is prior to the gauge?

2-if needle valve were sticking or floats were stuck wouldn't i still see pressure on the gauge?

3-(okay, i know i said 2 but i can't help myself!) would the pump getting air instead of fuel cause this (say from fuel sloshing in tank?)? if it is possible why would it take so long to clear the problem?

[911pcars]

1-if pressure gauge shows -0- then can i assume problem is prior to the gauge?

Yes. There is either complete blockage of the fuel passage or zero pressure from the pump.

-if needle valve were sticking or floats were stuck wouldn't i still see pressure on the gauge?

If any needle valve(s) were to stick wide open, there would be reduced resistance and the pressure would decrease. You would also be pumping raw fuel into the engine via the float bowl served by the stuck valve.

3-(okay, i know i said 2 but i can't help myself!) would the pump getting air instead of fuel cause this (say from fuel sloshing in tank?)? if it is possible why would it take so long to clear the problem?

The pump is located at or below the level of the tank. How much would fuel have to slosh for the pump to ingest air? A lot, like a tsunami-induced wave. Hardly normal or typical unless one were Scott Dixon on the last lap of the Indy 500. And if the tank had any quantity of fuel, the chances of ingesting air from fuel sloshing are pretty much nil.

c h e c k t h e p u m p and/or the pump electrical connection. Disconnect the outlet and run the fuel into a container or back into the tank. Prod, shake or otherwise jiggle the fuel pump and see if that interrupts the fuel pump. An internal electrical malfunction would cause it to overheat and momentarily make it in-op.

BTW, a carburetor will supply fuel to the engine for many seconds without fuel pressure from a full float bowl - I'd say at least 20 seconds with the fuel pump OFF before you'd feel any symptoms of running out of fuel (depends on rpm). Your fuel system is exhibiting that same symptom (fuel pump works sporadically, enough to fill float bowl, then not).

Sherwood