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Sudden Loss Of Psi On Airtex E8012 Sx Pump

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I bought the following electric pump for my 240z with 3 screws SU CARBS:

 

https://www.amazon.com/gp/product/B000DT7Y7A/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1#

 

Initially the pump measured 4.2 psi which was a good pressure for both carbs. Mechanic left the car in on position without starting the engine and now the pump is just measuring 3.2 psi and causing backfire from the intake.

 

What could be the cause of this sudden loss of pressure?? the pump is still working but at 3.2 psi.

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SU's don't require pressure, they require volume. 3.2psi should be perfectly adequate, assuming the pump is still pushing an adequate volume of fuel. To test, run fuel line from pump into a one litre bottle, turn it on and see how long it takes to fill the botle , spec sheet seems to indicate it should take 30-40 seconds

 

Spec sheet also says it produces 9psi, are you running some form of pressure regulator ?

Edited by 1600dave

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SU's don't require pressure, they require volume. 3.2psi should be perfectly adequate, assuming the pump is still pushing an adequate volume of fuel. To test, run fuel line from pump into a one litre bottle, turn it on and see how long it takes to fill the botle , spec sheet seems to indicate it should take 30-40 seconds

 

Spec sheet also says it produces 9psi, are you running some form of pressure regulator ?

Spec sheet is wrong. WHen i bought this pump new it measured 4.2 psi right before the  carbs. I want to know if its possible that the pump lost pressure due to leaving the car in the on position and not starting it right away.

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Spec sheet might be right and your pump is just a dud, faulty out of the box, which may be why you're getting variable results from pressure ? I can't imagine how leaving it on would affect it. Again, it won't effect how the car runs, assuming volume is OK.

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Still cant understand why this pump has lost volume. Its the third time i replace this pump which initially dialed 4.2 psi and now due to leaving it running without cranking the engine diminishes to 3.2 psi

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SU style carbs only need between 1.5 and 3.5psi to operate efficiently. The higher pressure may have damaged the needle and seat allowing fuel to push past it which would account for the lower pressure you are getting now and causing the engine to overfuel. Put a pressure regulator on it set to 2.5psi and replace your needles and seats. Also make sure you have the return line plumbed in.

By the way: You were having fuel pump problems on Classic Z Car Club back in November 2014 when it was recommended to you to get a Mazda RX7 pump because they run quiet.

( After 3 years I would get a better mechanic).

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How do you know if the needle and seat is damaged or not? I took one of them out of the float lid and blew some air and the stem was indeed working! Please advise.

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SU style carbs only need between 1.5 and 3.5psi to operate efficiently. The higher pressure may have damaged the needle and seat allowing fuel to push past it which would account for the lower pressure you are getting now and causing the engine to overfuel. Put a pressure regulator on it set to 2.5psi and replace your needles and seats. Also make sure you have the return line plumbed in.

By the way: You were having fuel pump problems on Classic Z Car Club back in November 2014 when it was recommended to you to get a Mazda RX7 pump because they run quiet.

( After 3 years I would get a better mechanic).

i thought 3 psi was still low. How can i verify that both the front and rear needle and seat are in working order? I ordered a new set from amazon.

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If you put a clear plastic hose onto the float bowl you can tell the height of the fuel in the bowl.

If the fuel level is right, the needle and seat are doing their job.

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Try mounting the pump lower as to be below fuel level in tank and without a big over loop in the fuel line. Never use thread tape on any fuel union. I don’t have much faith in those types of universal pumps or filters. If all else fails go back to a factory mechanical pump.

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I really need a steady 4 psi electric fuel pump. Is this carter 4070 any good? I read its noisy but will it give me the required 4 psi?

post-106003-0-35429400-1520428779_thumb.png

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Recently purchased a couple of Airtex 8012SX which advertise as 5.5 to 9 psi. Once plumbed into the fuel lines when measuring the PSI before the carbs, the fuel pressure gauge reads 3.2 psi. I guess this company must be going through quality control issues:

 

https://www.summitracing.com/int/parts/atx-e8012s/overview/

 

I was recommended a Carter 4070LP fuel pump:

 

https://www.summitracing.com/int/parts/crt-p4070/overview/

 

Will this pump provide a steady 4 to 4.3 psi??? I just dont want to be wasting money and effort on cheap non feasible electric pumps.

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Ok buy the carter pump and a 40 micron pre pump filter and a low pressure fuel pump regulator and screw up the install of said parts and proceed to blame them for your problems and whinge about the waste of money. When all this is done then, with the grace of God and he that is holy will you purchase a STANDARD MECHANICAL PUMP???????

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Posted (edited)

Why do you want 4psi ? SU's require virtually NO pressure to work.3.2psi is perfectly fine, I would even say 4.2psi is bordering on too high, especially if needle & seat aren't in 100% condition. Fuel pressure is definitely NOT causing a backfire from the intake, something else is not right to cause that.

 

Have you checked everything else in the fuel system ? Are you sure you don't have any minor restrictions / blockages / kinks / etc (anything that may restrict flow between pump and carbs) ? Your pump may be putting out 9psi, but that 9psi isn't making it to the carbs ? Have you tested output from the pump at the pump, not at the carb after running it through near 50 year old plumbing ?

 

Regardless, you don't need 4 psi or even 3 psi, I guarantee you I could get an SU to run perfectly with 0.1 psi.

Edited by 1600dave

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Please people stop trying to help this clown he will not listen to you. Just look at all of his other threads!

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Why all the hassle with retro-fitting an electric pump on a 240Z with SU carbs? Just bolt on the stock standard mechanical pump and away you go, no hassles, no dramas, happy driving and never look back. :)

 

Car companies know a few things about designing and building cars, far and away more than backyard DIY car owners, the stock standard Z fuel system works, don't fix or mess with what ain't broke. ::)

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