Fuel pump fluctuation

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Fuel pump fluctuation Empty Fuel pump fluctuation

Post  Tore on August 11th 2012, 11:56 am

I have a HOlley Black pump and sometimes it runs right at 7 pounds regulated. Then sometimes it goes to 3 pounds and creeps up to 7 very slowly. Is this a sign the pump is taking a dump? The fuel pump is on a relay circuit so it gets non fluctuating voltage.


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Post  richter69 on August 11th 2012, 12:03 pm

are you checking pressure before or after the regulator?
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Post  69F100 on August 11th 2012, 3:18 pm

Tore wrote:I have a HOlley Black pump and sometimes it runs right at 7 pounds regulated. Then sometimes it goes to 3 pounds and creeps up to 7 very slowly. Is this a sign the pump is taking a dump? The fuel pump is on a relay circuit so it gets non fluctuating voltage.


Tore

Tore I was having the same problem with mine take the inlet filter out it is behind the inlet fitting mine was stoped up I just removed it ( it want be worth using when you get it out or mine wasn't) as I have a filter before the pump now. also take the i beleave it a brass srew with the spring behind it check and make sure everything is clean in there.
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Post  Tore on August 11th 2012, 6:42 pm

richter69 wrote:are you checking pressure before or after the regulator?


After the regulator.
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Post  Tore on August 11th 2012, 6:43 pm

69F100 wrote:
Tore wrote:I have a HOlley Black pump and sometimes it runs right at 7 pounds regulated. Then sometimes it goes to 3 pounds and creeps up to 7 very slowly. Is this a sign the pump is taking a dump? The fuel pump is on a relay circuit so it gets non fluctuating voltage.


Tore

Tore I was having the same problem with mine take the inlet filter out it is behind the inlet fitting mine was stoped up I just removed it ( it want be worth using when you get it out or mine wasn't) as I have a filter before the pump now. also take the i beleave it a brass srew with the spring behind it check and make sure everything is clean in there.

I will take a look at that.

Thanks Tore
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Post  richter69 on August 11th 2012, 6:52 pm

i assume this is w it running also?
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Post  bbf-falcon on August 11th 2012, 8:03 pm

Erratic Fuel Pressure
Race Pumps do not work well with bypass style regulators. The fuel pressure will be erratic.

If the engine has erratic fuel pressure for a few minutes after re-starting and clears up the problem is likely from loosing prime.
Fluctuating fuel pressure at idle (unless you have a bypass style regulator) is usually due to a vacuum leak in the inlet line. Test this by replacing the inlet line with a short line to a 5 gallon fuel container….if it clears up, you have a vacuum leak.

. MagnaFuel considers excessive fluctuation to be over 1-1/2 pounds of pressure. Vibration, aeration, faulty gauges, or sharp changes in supply/pump pressure usually cause this. You should isolate the regulator with rubber mounting to tame vibration.

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Post  whitefield on August 12th 2012, 11:20 am

Mine fluctuates from 7to 8 lbs and the needle on the gauge is moving rapidly. I have a mallory pump and regulator with a returnable fuel system. Filter before the pump and fuel PSI gauge comming of the port on the psi regulator . It just started last season doing this.

P. S. Sorry didn't mean to jack your thread O.P.
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Post  Doug Rahn on August 12th 2012, 11:33 am

Also check out the regulator real good. I just changed the diaphragm and spring in my bypass regulator and it's back to rock steady. cheers
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Post  Tore on August 13th 2012, 11:07 am

richter69 wrote: i assume this is w it running also?


Yes it is.
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Post  Tore on August 13th 2012, 11:08 am

Thanks for the input fellas.


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Post  bbf-falcon on August 13th 2012, 2:09 pm

NP you streaker Laughing

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Post  jasonf on August 13th 2012, 3:11 pm

That is interesting. The blue pump in my tbucket does the same thing. Sometimes it is 6 1/2 psi then sometimes it will be down to 3 psi. That is at the carb after the regulator. I never notice any difference in performance though..
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