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  • Fuel Pressure Issues During Start-up

    At AutoX on Sunday the 240 randomly decided to stop starting mid way through the day. Every time that I ever start the car, I turn the key to the ON position and wait for the pump to prime/pressure before cranking.

    The GF happened to be in line for her run when it happened, so I got in, primed the pump twice (I know it shouldn't make a difference), then started it by using some gas pedal while cranking.

    I figured it was just a random occurence, but it happened again the next time that the car was turned off. I opened up AEM and played with the crank advance while starting and added some fuel thinking that it may just not be getting enough fuel during cranking. The car started twice, then stopped starting.

    After this I pulled the AEM FPR apart and checked the bladder. There was no fuel in my vac lines, and the bladder looked fine. After this I noticed that when the pump would prime, I could watch the fuel pressure gauge pressure up, then drop to almost zero. The car now starts randomly if you sit there priming and cranking until it randomly gets enough fuel.

    I figured that it may be a FPR issue, since when the pump primes I see pressure, then it drops off pretty quickly. I finished the day by just bump-starting the car before each run. The car starts no problem when bump-started, and when driving, I get the 42psi base, which rises and falls with boost/vacuum as per usual. Setting base pressure is not an issue, and my pressure and AFR look fine while driving. The only time that I'm getting an issue is when it primes/pressures to start.

    Am I wrong in thinking that my FPR should hold the pressure from tank to fuel rail before cranking? And if it is a FPR issue, why is it only before starting, and why do I have no issues during operation. I guess that the ball could be leaking into the return line when sitting with static pressure, because I'm pretty sure that the bladder is in perfect condition. I rebuilt it with a new bladder/ball about a year ago before installing it.

    Is there something else that I can check? Is there a check valve on the pump or something silly that I just haven't thought of. It's a Walbro 255. I can't imagine that the FPR is the issue, since it holds pressure normally during operation, but maybe that's just the pump working overtime to maintain pressure once the car is running, and hiding the leak-off issue that I'm seeing before starting? Any thoughts? Thanks guys.
    In Zipties We Trust....

  • #2
    http://nissanroadracing.com/showthread.php?t=2722

    Start there.
    98 240SX SCCA STUish

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    • #3
      Apparently my gauges decided that they didn't want to work today, so I only had the analog gauge on my FPR to work from, but I think I found my issue. I pinched the return line running from the FPR and was able to see 100psi+ during prime. Once I took the vice-grips off the pressure quickly zero'd.

      I pulled apart the FPR again and found this wash-out on the restrictor. Seems very strange to me, but it looks like the ball-seat on the restrictor has washed out on the left side in this pic. The mark runs about 1/2 of the left side, and just slightly on the opposite side. Looks like I'll be trying another FPR if I can find one in the area, or maybe just get another rebuild kit for this thing. Since the system held pressure with the line pinched, looks like it was the FPR leaking through the restrictor/ball.

      Have any of you guys seen a wash of a restrictor like this before?

      In Zipties We Trust....

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      • #4
        I was hoping that I could swap the restrictor out for the old one that I had from the previous re-build. Turns out that they used to use a flat seat instead of a ball seat so I won't be swapping it out tonight. They do provide a few other sizes of restrictors, but nothing I can use.





        In Zipties We Trust....

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        • #5
          It's hard to tell from the pic. Is the seat all pounded out on the side so it won't seal? Seems that they don't use hard enough metal for it if that's that's the case.
          98 240SX SCCA STUish

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          • #6
            It is hard to see, but if you look at the left side of either of the first two pictures, you'll see that the ball seat is "shiny" and wider in a "half moon" type shape. The ball on the bladder would have been sealing on about half of the seat (other side), while there was a flow area on that side for fluid to rush/leak past.

            If fluid were leaking past over a long period of time, it would basically "sand blast" the area, which is why only half is damaged like this. I think that after that side became worn down so far, the ball was able to move into the groove a little, which is why there is a small wear area directly across from it from fluid moving through that side.

            You're right, the metal or the surface treatment wasn't hard enough and eventually the leak-off was noticeable enough to hinder starting. I don't think that pounding on the seat did it unless the spring above was misaligned quite a bit over a long period of operation, since the leak path is pretty localized. Maybe there was a bit of damage on the one side, or a piece of debris jammed in there, which allowed the leak on one side, and eventually got larger over time. Maybe overthinking it a little, but it seems like that's why it washed out as it did.
            In Zipties We Trust....

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            • #7
              Here are a few images that show it better. First two are of the bad side, 3rd is from the less damaged side.





              In Zipties We Trust....

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              • #8
                For what it's worth,. some 255 cars just need an inline check valve to keep PSI. I wouldn't worry much.
                'Slicks on a car show me you care - broken axles show me you're trying'
                [I]Nitrous Rental Cars - Turbo Festivas - Vehicular Lunacy[/I]
                [SIZE="3"][B][url]www.sloppymechanics.com[/url][/B][/SIZE]

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                • #9
                  Most pumps havr a check valve in them to hold fuel in thr supply line and keep it from draining back into the tank. it would awnset your problem of running fine once startefbut hard to start after turning off.

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                  • #10
                    Turns out that the ball seat in the restrictor was washed out. I posted pics above, once I replaced this everything was fine.
                    In Zipties We Trust....

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