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Old 23-05-2018, 02:09 PM   #1
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Fuel pressure on RB25DET

So I installed a greddy manifold and fuel rail on my RB25DET Neo and I’m having trouble setting the correct fuel pressure (43psi without vacuum). Every time I try set it the needle on the gauge flutters like mad. I can set the fuel pressure just below 40psi and the needle stays still. As soon as I go 40 or above it flutters. I had a cheep Fuel Pressure Regulator on at the start and maybe thought that was it. So I put a malpassi/sytec FPR and gauge and still flutters. I also put a new fuel pump on(Walbro 450/455). I put a new fuel filter in and the flutter lessened but it’s still there. I am running an6 lines. I’m thinking maybe a leak somewhere but I can’t see any fuel.
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Old 25-05-2018, 09:07 PM   #2
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You tried a different gauge? Fuel pressure problems can be a pain to source.

Have you still got the fuel pulse dampers fitted to the return line?
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Old 30-05-2018, 10:15 PM   #3
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You tried a different gauge? Fuel pressure problems can be a pain to source.

Have you still got the fuel pulse dampers fitted to the return line?


Tried 3 different gauges same result. yeah I have the damper on the return I want to take it off but not sure the best way to connect the ends of the two hoses? With a solid piece of pipe? Yeah itís been a bitch to try find out to say the least lmao !
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Old 30-05-2018, 10:39 PM   #4
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Have you tried a glycerin filled gauge, it may damp out the fluttering.
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Old 31-05-2018, 01:54 AM   #5
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Have you tried a glycerin filled gauge, it may damp out the fluttering.
Yeah they were all glycerin filled, I put a new fuel filter on and the flutter lessened. would a blocked injector cause that? Maybe a piece of threaded tape from the fittings? just donít understand whatís wrong itís really annoying the shit out of me. Iíll try meaure the voltage at the pump see whatís happening there. the gauge flutters at round 40psi and above. Maybe something canít handle the higher pressure but I canít see any leaks.
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Old 31-05-2018, 08:55 AM   #6
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Hi. Have you had a good look at the hose/clamps connecting the fuel pump to the outlet of the tank it could be holding pressure fine up to 40 psi then when the pressure increases the fuel could be making its way out under a hose clamp. There would be no sign of a leak from the outside of the tank.
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Old 31-05-2018, 10:49 AM   #7
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Couple of things to check, is the pump receiving 12v at idle, sounds silly but your sure you have the FPR the correct way around, most FPR use a diaphragm, spring and ball valve to control pressure, but obviously this would be unaffected by vacuum when setting, but if its happened when using more than one FPR the problem mush be in the supply.
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Old 01-06-2018, 03:05 AM   #8
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Iíll check the hoses at the pump. It was fluttering before I changed the pump but itís worth a check.

I have tank > filter > rail > fpr > return
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Old 01-06-2018, 10:33 AM   #9
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Out of curiosity what make and size injectors have you go installed, and is the FPR attached to the end of the fuel rail? you could try running some pipe from the end of the rail to the FPR IE running it remote, this may damp the pulsations a bit.
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Old 01-06-2018, 03:12 PM   #10
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Out of curiosity what make and size injectors have you go installed, and is the FPR attached to the end of the fuel rail? you could try running some pipe from the end of the rail to the FPR IE running it remote, this may damp the pulsations a bit.

Standard NEO injectors. Not attached to rail directly,have about 2ft maybe of an6
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Old 01-06-2018, 05:40 PM   #11
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Standard NEO injectors. Not attached to rail directly,have about 2ft maybe of an6
Well that quashes that theory, its an odd one, maybe change or temporarily eliminate the fuel filter just to make sure its not the culprit, the pump should be easily capable of delivering 80psi, starting to wonder if there is something not right with the FPR.
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Old 01-06-2018, 07:49 PM   #12
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Well that quashes that theory, its an odd one, maybe change or temporarily eliminate the fuel filter just to make sure its not the culprit, the pump should be easily capable of delivering 80psi, starting to wonder if there is something not right with the FPR.


Iím sure the FPR is fine tbh, as Iíve said thatís the third fpr Iíve tried and Iíve even tried mix and matching the gauges. Yeah it is weird itís pissing me off big time haha.
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Old 01-06-2018, 11:46 PM   #13
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Damo could be onto something with the hose leaking in the tank from the fuel pump outlet theory

Had a similar issue with an evo recently where they have an o ring that seals the pump outlet to the pump carrier then sends it to the feed line. That o ring had squashed and it was leaking fuel back out into the tank again and it was a ******* to get to hold stable pressure at idle and then it refused to rise fuel pressure when on boost, it did the opposite and dropped pressure. Finally tracked the problem to the oring at the pump outlet, changed it and stable rising fuel pressure was restored.

Id check your jubilee clip at the pump outlet hasn't cut the hose and causing it to leak inside the tank when under higher pressures.
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Old 23-06-2018, 07:03 PM   #14
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Couple of things to check, is the pump receiving 12v at idle, sounds silly but your sure you have the FPR the correct way around, most FPR use a diaphragm, spring and ball valve to control pressure, but obviously this would be unaffected by vacuum when setting, but if its happened when using more than one FPR the problem mush be in the supply.
How do I check the pump voltage? at idle? I have a multimeter here. Thereís two plugs going into the tank which plug do I test?
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