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#1
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4.8is fuel system blues
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#2
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This sounds like a syphon jet issue. Just do a search on this site there is a ton of related info.
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1988 325is (purchased new) sold 2004 X5 3.0 2005 X3 2.5 2008 X5 3.0 (new to me) |
#3
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Thanks, so the siphon jet would actually cause performance issues? Will try searching.
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#4
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Yep, but I guess it would be more accurate to say "syphon jet plumbing."
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1988 325is (purchased new) sold 2004 X5 3.0 2005 X3 2.5 2008 X5 3.0 (new to me) |
#5
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The siphon jet pump really only matters when you are below about a third of a tank (guess on the exact number there). So if you keep your tank filled at half way or higher, and you still have problems, that should rule out the siphon jet being the only problem you have.
If keeping the gas tank > 1/3 full means the problem goes away, then it reappears if you let it get below that, that would be a very simple and conclusive test that the siphon jet pump is faulty. Andrew Wynn has a great thread on here somewhere with photos and graphics to show you how the pumps and fuel tank work, which should make sense of this. Here's a good thread on the siphon jet repair, with links to that AndrewWynn thread in post #1: https://xoutpost.com/bmw-sav-forums/...flon-wrap.html What brand of fuel pump did you use when you replaced yours? Pierburg was the original manufacturer, bought out by TI Automotive, so either of those are good. The loss of fuel pressure after shutting down may be an important clue. I think the pump has a check valve in it, so loss of pressure may indicate a problem with it holding pressure.
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2001 X5 3.0i, 203k miles, AT, owned since 2014 Last edited by oldskewel; 03-26-2021 at 09:15 PM. |
#6
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Engine running fuel pressure is determined by the syphon jet relief valve so a leaking syphon jet o-ring (for example) could result in up to 8 PSI drop (down to fuel pressure reg setting) in engine running fuel pressure, AND explain the noise from the left side of the fuel tank.
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1988 325is (purchased new) sold 2004 X5 3.0 2005 X3 2.5 2008 X5 3.0 (new to me) |
#7
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Thanks 80s Tech! That is exactly what I think the issue is. I am sure that the noise is coming from the very top of the tank where the pressure release valve is. And I was under the impression that the fuel pump is before the fuel filter/pressure regulator so the residual fuel pressure would be held between the pressure regulator of the fuel filter and the pressure relief valve on the siphon jet assembly. Since I recently replaced the fuel filter/regulator, the only other pressure point would have to be the fault relief valve.
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#8
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You have the right idea but the pressure relief valve is in the fuel pump well on the right side of the tank. The valve itself is probably not the fault and it's more likely the O-rings/seal, on the left side that you say the noise is coming from, which feeds the syphon jets. If you have a look at the fuel diagram in the Bentley manual (or posted here) and pull the left side apart it will start to make more sense. There are a lot of posts/threads about this on the forum as well.
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1988 325is (purchased new) sold 2004 X5 3.0 2005 X3 2.5 2008 X5 3.0 (new to me) |
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