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Post by Monkey on May 19, 2015 11:00:28 GMT 1
Any idea as to what low pressure I should have before the fuel filter? I had 0.5 bar when I first started the engine cold but after it got warm I had almost 4 bar!
I can't find any data referring to it.
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Post by Noberator on May 19, 2015 11:35:37 GMT 1
Any idea as to what low pressure I should have before the fuel filter? I had 0.5 bar when I first started the engine cold but after it got warm I had almost 4 bar! I can't find any data referring to it. Monkey this Golf hasn't been misfueled at any time that your aware of causing damage to the HPFP.
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Post by Monkey on May 19, 2015 16:16:53 GMT 1
The customer did mis fuel it a while back but didn't start it, I drained the tank and refuelled it but I'll point out this fault has been on going before that happened.
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Post by valhalla on May 19, 2015 21:20:55 GMT 1
It sounds like you LP fuel system is knackered. If the pressures you quote are gauge (that is, on top of atmospheric), then 4BAR is a bit too high, and 0.5BAR is way too low. Assuming that pressure tapping is the correct one, and not the spill-return line from the filter, then there's something seriously wrong with with this fuel supply, a kink or blockage somewhere in the return line and/or fuel cooler circuit or some sort of thermostatic problem at the fuel cooler. It sounds like you are in for the long-haul on this one....
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Post by Dragon on May 19, 2015 21:59:00 GMT 1
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Post by valhalla on May 20, 2015 23:45:46 GMT 1
A very useful document, and one which answers the questions very nicely.
In short, although the document does not go into detail on it, the "pressure retention valve" at the injector spill rail is the important element here. If it fails open, it will affect the injectors for fuel duration of injection (the needle will not open or close correctly on each injector). More importantly, it will flood the spill-return rail from the HP pump to the filter assembly with a higher flow of fuel than would be calibrated, leading to control problems on the HP pump.
No pressures quoted for first and second stage pumps exactly, only a total of 5BAR to the HP pump. So that's the pressure to measure, after the second (underbonnet) fuel pump. If that checks out OK, a pressure test at the injector spill rail into the "pressure retention" valve inlet would be the next port of call. Too low means a failed valve, too high could be a kink or restriction back at the filter assembly, which is where the clever stuff seems to happen for the regulation of fuel temperature.
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