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  1. #1

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    Lightbulb External DI/FICHT Adjustable Fuel Pressure Mod

    Background

    The intank fuel pressure regulators fall off on ALL DI machines requiring the fuel pump assembly being removed in order to install a threaded hose barb to reattach the factory fuel pressure regulator back to the return line. The FICHT fuel injected motors require 20-30 psi and if the pressure drops you run the risk of melting a piston. The process of removing this assembly is very time consuming.

    A Kawasaki inline fuel pressure regulator was looked at but inconsistencies with pressures caused this idea to be kicked.

    Recently, I discovered that my factory oem fuel pressure regulator is failing. It is making a noise probably due to degradation of the internal seat. Additionally, pressure is down to 22 psi, on the low end of wear it needs to be.

    Researching for a replacement oem style fuel pressure regulator turned up only used units, which may have the same issues, or one from Quantum that they sell separately or as a kit with the fuel pump. The cost on this standalone fuel pressure regulator is $30 while used ones range from $70 and up.

    https://www.ebay.com/itm/Quantum-Fue...4/382119725116

    Modification
    What is required is a simple standard aftermarket EFI fuel pressure regulator. While expensive units such as AEM, AeroMotive, and others fetch upwards of $100, cheap copycats sell for as little $15. The cheap copycats tend to drift, meaning that if you set it at 25 psi, you will end up with 23-27 psi, which is fine for our application. Most come with a built in dial and could easily be mounted directly underneath the hull where the front opening is that the seat normally covers.

    https://www.ebay.com/itm/UNIVERSAL-1...D/292287757425

    https://www.ebay.com/itm/JDM-Adjusta...l/291795399862

    Plumbing is fairly straightforward, using NPT barbs, fuel comes from the injectors to one of the in/out ports and you plug all of the other in/out ports. The return port returns to the tank using another NPT barb. The 1:1 boost port is capped with a silicon cap to avoid water entry.

    Has anyone tried this approach and can anyone see any reasons why this would not work.

    I would rather put one of these in, where I can check the fuel pressure anytime I start the ski, rather than not know if the factory FPR is doing it's thing.


  2. #2
    Click avatar for tech links/info K447's Avatar
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    I recall replying years ago to a similar proposal for repair.

    My concerns are primarily around safety. An external fuel pressure regulator is external to the fuel tank, but inside the hull. If the modified fuel system leaks for any reason there will be flammable and potentially explosive gasoline fumes inside the enclosed hull.

    Not only will there be additional fuel hose connections and clamps, the external regulator must be securely mounted so that it will withstand hard riding conditions.

    Automotive external fuel regulators are engineered assuming that there will be unlimited ventilation. If it corrodes or a seal goes bad, the leaking fuel just drips onto the ground. In a PWC there is effectively zero ventilation to clear fuel leakage fumes.

    I did have a cheap aftermarket pressure regulator sitting on the shelf here, new and unused, and it began to rust. Just surface rust, but clearly it would not have been suitable inside a damp PWC hull.

    Whatever you install needs to withstand worst case conditions.

  3. #3

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    That is why I am looking at billet aluminum. I have a friend with a turbo ski that has been running one for years without an issue.

    Of course, fuel leaks are always a concern. This would effectively replace the schrader valve tee, use sealed NPT fittings and oetiker clamps on the barbs. Mounting of course would have to be sturdy. I have yet to see a billet style ever leak, but YMMV. I personally run an AeroMotive on one of my tuned cars. On that note, I have seen many schrader valves leak on tires, so I think the risk relatively equal on that front. But that is also my opinion.

    And I for one, check inside the hull everytime I ride . . . you just never know.

    Besides those concerns, do you think there are any other issues that I might be missing?

  4. #4
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by bfarnam View Post
    ... billet aluminum. ...

    ... any other issues that I might be missing?
    Is there some minimum fuel flow rate that the regulator may depend on to control the pressure?

    I do not know how much actual fuel flow there is through the OEM Ficht pressure regulator when the engine is at full song.

  5. #5
    martincom's Avatar
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    I've had a number of the Polaris direct injected watercraft and I've never had a regulator, itself, fail. Actually, though your fuel pressure was a tad low, 22 psi, when the regulator was supposedly failing (making noise), is still acceptable. I'm thinking it was probably some gunk, from old fuel, that was humg up in the regulator, creating an orifice that was producing the whistle.

    Your stall fuel pressure seemed very high for an OEM pump--more like a Quantum replacement pump So it makes wonder if it had been replaced with a Quantum package that included a replacement regulator. The only regulator failure I can recall reading about here, on GH, was with a Quantum replacement regulator.

    In my opinion, you're going through an awful lot of work and expense to repair something that has an extremely low failure occurrence---probably as low or lower than the components you'll be replacing it with.

  6. #6

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    I have never seen a FPR fail either. That is why I am surprised. I also thought about the gunk issue, but the interesting thing is that it seals 100% and doesn't leak fuel at all until the spring opens at pressure. I tried cleaning it with carb cleaner but that didn't help. I guess there could be something in there that is causing the whistle and vibration when open. However, I don't like the PSI that low - tells me the spring is getting weak.

    I was unaware of the Quantum FPR failures.... hmmm

    The pump is I believe is OEM and it does have the OEM markings (date code followed by 253 if I remember) - I have had physical possession of the PWC since May or June of 2017, I believe since before Quantum started selling the pumps. Amperage measurements are close enough to be a OEM pump.

    It is a bit of work I suppose - but then again we don't buy Polaris because we don't like work . . . LOL

    So the question remains, Quantum FPR, aftermarket Adjustable FPR, or used OEM FPR?

    As far as Adjustable FPRs and flow rates. On a dead head system the FPR flow rate must be sufficient to support the amount of fuel being consumed. On a return system as we have, the FPR flow rate must be sufficient to support the maximum flow rate of the fuel pump in order to not cause an elevated pressure.

    The maximum flow rate of the fuel pump, although truly unknown, could be approximated using the diameter of the fuel lines and the pressure. However, the math is not a simple as it sounds and variables are many. But generally speaking most adjustable FPRs use -6 or -8AN lines (1/2") which can carry far more than our puny little 1/4" lines (-4AN). Pressure loses would be minimal if non-exixstent.

    For those that wonder how much our little engine eats, a very simple method for a 2 stroke engine is to multiply the max HP by 0.1138; 135 hp x 0.1138 = 15.363 GPH. (From Nautical Monkey) That seems a little high.

  7. #7
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by K447 View Post
    Is there some minimum fuel flow rate that the regulator may depend on to control the pressure?

    I do not know how much actual fuel flow there is through the OEM Ficht pressure regulator when the engine is at full song.
    Quote Originally Posted by bfarnam View Post
    ...

    As far as Adjustable FPRs and flow rates. ... On a return system as we have, the FPR flow rate must be sufficient to support the maximum flow rate of the fuel pump in order to not cause an elevated pressure.

    ...
    Pressure regulation across the flow range from minimum flow to maximum.

    Unlike traditional automotive style fuel injectors, the Ficht injectors use the supply fuel pressure simply to ensure the injector RAM piston is able to refill with fuel on every solenoid return stroke. I do not know the precise minimum fuel pressure required to do this.

  8. #8

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    Quote Originally Posted by K447 View Post
    Pressure regulation across the flow range from minimum flow to maximum.

    Unlike traditional automotive style fuel injectors, the Ficht injectors use the supply fuel pressure simply to ensure the injector RAM piston is able to refill with fuel on every solenoid return stroke. I do not know the precise minimum fuel pressure required to do this.
    That is exactly how a return fuel system works. First we talk about "rail" pressure vs. "effective" pressure. The rail pressure is what we measure with a fuel pressure gauge via the schrader valve. However, the effective pressure is the pressure differential across the injector at different demand rates. You do NOT want this to change. The effective fuel pressure must be maintained at a constant rate to ensure proper fuel flow into the injector so that the injector doesn't "starve" at different flow rates. Flow rates are determined by the supply pump and the line sizes.

    The ability to refill the RAM piston has more to do with flow rate than pressure. If the system can not supply the proper amount of fuel to the injector RAM piston, it will not fully refill no matter the pressure.

    Now the small FPR inside our tanks is nothing but a simple spring and diaphragm or spring and ball/seat pressure regulator, much like a poppet valve. It remains closed until the pre-set pressure is applied and then slowly opens up until it is fully open to maintain the proper pressure. It actually more closely resembles a diesel relief valve in design.



    This style is very prone to pressure spikes, a very brief increase in the system just before the spring opens. If you put a pressure gauge on the schrader valve, turn on the pump, you will see the pressure very briefly peak then level out once the valve opens.

    This style is also very prone to pressure dips, a very brief loss of pressure during demand just before the spring reseals the valve. These fluctuations can cause damaging effects on fuel flow. On a side note, the size of the orifices is designed to maintain the proper flow rate at the rated PSI so as to minimize the pressure dips.

    When switching to a bypass regulator, the fuel will pass through the injectors and into the "IN/OUT" ports on the FPR. A spring holds a diaphragm closed blocking the return flow to the tank. The spring pre-tension is set by a locking set screw. Since the return fuel flow is blocked, the pressure will build. Once the pressure starts to overcome the preset spring tension, the diaphragm slowly opens letting fuel through the return port back to the tank in order to maintain a constant pressure. During periods of high demand when pressure starts to drop below the threshold, the diaphragm will start to shut raising the pressure back to the specified pre-set pressure. This cycle repeats over and over ensuring that the set PSI is always available on the fuel "rail" for the injectors. This type of regulator is more accurate than a poppet, is not prone to pressure spikes or dips, and doesn't impede or change the flow rate available to the injectors since that is determined by the pump. This is because the larger diaphragm size allows more gradual opening and closing vs the poppet style. You will not see a pressure spike or pressure dip across the entire flow range.
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    Last edited by bfarnam; 08-10-2020 at 10:04 AM. Reason: spelling and grammar - duh

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