SC fuel pump: can run but still fail?

Formerly Steve Wilkinson · 08-19-2001, 01:13 PM

'83 911SC wouldn't start last night on the way home from a dinner, and since my non-drinker wife is my live-in designated driver, she was in the left seat. Sure she'd broken something, she vowed never to drive the damn thing again. Anyway, it's obvious there's no fuel to the engine: PMO carb float-bowl windows are dry and the engine-compartment pressure gauge reads zero with the key on and the fuel pump buzzing away. I'm assuming there's a diaphragm of some sort inside it that has given way, probably during the two years of restoration when it sat dry? Should I simply immediately buy another pump, or is there any possibility of something else having failed, like a check valve?

Stephan

cabman · 08-19-2001, 01:18 PM

bad fuel pump is usually indicative of a car that starts and then immediately dies. is yours experiencing that symptom?

in other words, does the car even start at all? if not, i doubt it's the fuel pump

BruceSwanson · 08-19-2001, 08:16 PM

My fuel pump went bad on my 82SC. Sometimes it would start, run for a few minutes then die. Other times, the thing wouldn't even start. Tried replacing the fuel accumulator and check valve (cheapest) with no luck. Finally broke down and bought a NEW pump and it runs like a champ. Make sure you buy a new one. I had a rebuilt that lasted less than 2,000 miles. Waste of money.
Bruce

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Bruce
1982 SC

Superman · 08-19-2001, 10:40 PM

I think that a pressure gauge and volume beaker are probably needed to check the high pressure pumps for FI cars. But a pop bottle is usually all that's necessary for this test on carbureted cars. Of course, it sounds like your pump is electric instead of those diaphragm types but I still think it prudent to run the pump and visually see that a reasonably forceful stream comes out. Before you go buy a new one.

If that's not the problem then perhaps there is a plugged screen or filter.

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'83 SC

Formerly Steve Wilkinson · 08-20-2001, 06:20 AM

My question is not whether the pump is pumping gas--it isn't--but whether or not there is a diaphragm inside a 1983 911SC pump that can fail even though the pump is running, or whether there's a check valve or something that might be the problem. This is an SC with a modified engine that has PMO carburetors. I have a fuel-pressure gauge in the engine compartment, and it reads zero--no fuel coming through, and it's upstream of the filters (other than the relatively gross one in the bottom of the tank). The carbs have little glass windows into each float bowl. There is no gas to be seen through them. Hence testing for fuel flow or whether or not the engine starts and dies is pointless; there is no fuel coming to the engine. None.

Stephan

RarlyL8 · RarlyL8's Garage

Stephan,
Yes there is a check valve in the stock SC pump on the outlet side fitting. I presume you are using a regulator for the carbs. A better deal would be to use a pump made specifically for the carbs, lot less pressure.

gblumenstock · 08-20-2001, 10:54 AM

I just replaced the fuel pump on my 79 SC. (167K miles). The pump might have been stock for how it looked. I use the car as a daily driver so it came as a shock when the car would not start. The pump was making a much loader buzzing with the key on than the normal hum at startup. To make sure it was the pump making the noise, I pulled the red relay while it was buzzing. Yep, it was the pump. It would turn over and barely start before stalling. I simply replaced the pump with a new one ahd the car started right up after a minute of priming the system.

Sounds like you need a new pump.
GB