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New Question About Fuel Pump
- Thread starter vette
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Bob_Spidell
Yoda
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Haven't experienced this particular problem--yet--but I suspect the pump would tick very slowly and at a consistent interval. In theory, the pump would be pulling a vacuum and would tick a few times and stop, but I believe there is an internal bleed--or enough leakage in the flapper valves--so that the 'vacuum' would bleed down and and let the pump attempt to pump again. Also, since the pump is working against vacuum, the pump body would get heat-soaked pretty quickly and would eventually fry. When I've bench-tested a pump and held my thumb over the inlet port IIRC it behaves like I speculated.
OTOH, if there's an air leak on the inlet side the pump will fire erratically (that I HAVE experienced).
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No! I had a problem several years ago with a piece of coating that got loose and traveled all the way up to the highest point of my fuel line and stopped the flow. It was so bad that I had to cut out a 6" piece of fuel line and install rubber fuel line to fix it. Another time I had trash in the fuel tank and I just blasted it loose with an air hose to knock it out of the way. I then had the tank cleaned and it cleared up the problem.
Keoke
Great Pumpkin
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I think YES since the fuel bowls will eventually empty and the pump even though it gets no fuel will try to fill the empty fuel bows and just keep ticking??
A blockage in the fuel line between the pump output and the fuel bowl will act
like the fuel bowls are full to the pump and it should stop ticking??
OP
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Thanks for the responses. I can see we are on the fence with this just as I was. I tend to think as Bob & Patrick that if it is a complete blockage that the pump will pull a vacuum on the inlet side and the diaphram will not be able to move so the pump would be "lock up" and no sound. If it is not a complete blockage it would just slow down in which case the engine might still run but very weakly. So remembering the episode when I was sitting dead-in-the-water in the strangers driveway, I had no ticking on either pump. But when I left the ignition on to go around to check for spark, moments later there was a rush of ticking and the carb bowls filled up. It then fired right up. So it was definitely starved for fuel. I have a clear inline fuel filter just before the carbs. I never thought to look at it to see if it had fuel in it. I've gone over my electrical circuit connections and I can't believe they are the culprit. The electrical system in this car is only 2 years old and is built just as a new car's system is. Just for the record there is no sign of debris in the filter. Thanks again, Dave.
One way to test the two theories here would be to take another fuel pump and temporarily hook it to a power source. Block the inlet line with a cap or plug and see if the pump will continue to click. I tend to agree with Keoke that the pump will continue to click/run with a blockage on the upstream side of the pump.
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I installed an isolation valve in the fuel line between the tank and pump in case I have to remove the pump with a full tank. I'll shut the valve and let you know what happens with a complete blockage.
If the blockage isn't complete, the pump will tick slowly but not enough to keep up with the engine.
If the blockage isn't complete, the pump will tick slowly but not enough to keep up with the engine.
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Confirmed - With the pump suction completely blocked, it doesn't tick. With it partially blocked, it ticks slowly.
RAC68
Darth Vader
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Hi All,
Before hearing the results of John's test, I would have drawn the same conclusions as presented by Bob and Derek. John, did your test involve a Points SU or an Electronic SU pump?
For a Points SU, without fuel to buffer the sound, I would also have expected the pump tick to be quite noticeable and, due to a lack of fuel cooling, eventually burn up. However, if we are talking Electronic SU, it would have been smart for the designer to create a cutoff for heat buildup as well as pressure output to eliminate the problem of burning the pump due to overheating.
An interesting question.
Ray(64BJ8P1)
Before hearing the results of John's test, I would have drawn the same conclusions as presented by Bob and Derek. John, did your test involve a Points SU or an Electronic SU pump?
For a Points SU, without fuel to buffer the sound, I would also have expected the pump tick to be quite noticeable and, due to a lack of fuel cooling, eventually burn up. However, if we are talking Electronic SU, it would have been smart for the designer to create a cutoff for heat buildup as well as pressure output to eliminate the problem of burning the pump due to overheating.
An interesting question.
Ray(64BJ8P1)
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The tested pump is an electronic SU. They sound the same as a points SU. The "tick" sound comes from movement and stop of the armature in both cases. I
f the fuel pickup in the tank is completely blocked by debris, the pump would still be full of fuel, just like when I shut the isolation valve from the tank. I don't know about a heat cutoff. I have heard of the problem and didn't leave the valve shut for long. (Not willing to burn up a pump for this experiment.)