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Discussion Starter · #1 ·
Chasing a low fuel pressure issue with a 2006, 84K. Noticed a slow pressure drop with heavy pulls, starts at 64psi, drops to 47psi and the longer it runs the faster and lower the pressure will drop with a hard pull. Replaced the filters (MC), looked good, no junk any where or water in the drain, same pressure drop. I installed a blue spring kit long time age, replaced again, still no change in symptoms. Tested the fuel pump pressure at the HFCM outlet, 104 psi, flow was 750ml in a 20 second pump run. Checked flow at the test port, same 750 and no bubbles, looks like a garden hose stream but smaller. What have I missed? Suggestions? Thanks team.

WDP
 

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Can you perform a fuel pump inlet restriction test and be able to do it on a road test? This really sounds like you are losing volume and if everything you tell us is accurate then you will want to confirm you don't have a problem before the pump. You don't say what vehicle this is (year/model) and what is your fuel tank configuration and type?
 

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Discussion Starter · #4 ·
Checked the outlet flow, what is a inlet restriction test? 2006, 6.0 F250 screw with a 54 gallon accessory tank from AeroTank model Ford 1019. Thanks.

WDP
 

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Discussion Starter · #5 ·
AHA Ford Doc, when I installed that tank 7 years ago the piece if rubber fuel line to lower the fuel pickup to the bottom of the 3 inch deeper tank may not have been bio diesel compatible. Recently mandated bio and some 5% plus on occasion 20% may have done a number on that hose, swell and almost close up. Drop tank and check when the weather breaks. Thanks for the light bulb moment.

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Glad to hear that you may have found the problem! Keep us posted.

To answer your question on testing Inlet restriction it is a simple test that measures the vacuum at the inlet port of the fuel conditioning module. You tee in a vacuum gauge on the fuel pump inlet connection and measure the vacuum created under full load conditions. Dealers have the test hoses, gauges and the fuel system pressure and flow tester that makes this testing a bit easier. Most people will not have these test hoses. A reading above 6 in-Hg indicates a restriction and I would bet yours definitely exceeded that spec since you were seeing low fuel pressure. I have seen on some trucks as high as 30 in-Hg. If you run with both the vacuum gauge and pressure gauge connected you will see the restriction go up and the pressure drop at the same time.

Good Job! :thumbsup:
 

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Discussion Starter · #7 ·
Finally got it. Turns out the Ebay blue spring kit failed. The rubber seal on the brass regulator plunger tore and disintegrated. Watching the line pressure drop when the pump times out (not running) was the key. The ebay kit allowed the gauge to drop to zero in about 1 second. Replaced with a genuine Ford kit, pressure drop takes about 4 seconds. Only reduced by 6 psi on a right foot press to the floor. Add the blue spring kit to the critical parts list that should not be second sourced.
Thanks team!
WDP
 
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