Fuel Pressure dropping quickly while sitting

The White Spy

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Feb 19, 2015
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I have a 2.8l vr that has been hard starting for awhile now and I have been trying to get it to pass emissions (it finally passed!) so now I have been able to take the time to check on possible causes. It was throwing the code for an o2 sensor which had been cut on the harness side so I fixed that and replaced the sensor because it was bad as well. The local vdub mechanic told me the crank sensor was bad so I replaced that to no avail. Today I hooked up a fuel pressure gauge using a bypass and the car holds at 50 psi while running and jumps to about 60 psi when the vacuum line is off the FPR. All that being said the fuel system loses pressure and drops off to a little less than 2 bar while sitting. Any thoughts?
 

Crasher

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The enriched fuel pressure with an ABV engine should be 4 bar, dropping to 3.5 bar with vacuum so your delivery pressure figures are spot on. As far as the holding pressure is concerned, according to the manual

"After 10 minutes the pressure must not drop below 3 bar"

If it does drop, the procedure is to change the fuel delivery unit, I can get these from Febi quite reasonably.
 

The White Spy

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Would you be able to get a link to that? I haven't had a chance to see if one of the injectors is leaking but I don't see fuel dripping anywhere when I park it and look underneath. Another thing to note is when it had been running it starts right up again.
 

Keithuk

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You will only see external leaks for fuel, if an injectors is leaking that leaks into the engine and you won't really see it. You could remove the fuel rail with injectors in place and pressurise the system and look for dripping injectors. This would make the engine start on 3 cylinders because the excess fuel has wet the spark plug with fuel.
 

Crasher

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I don't have that fuel pump on my site at the moment due to eBay bringing in new listing rules that insists the parts listed are targeted using their expensive software so they can go and stick that where the sun doesn't shine! I know I can get them as I fitted one to a Golf 3 VR6 fuel tank that I fitted into a Golf 2 as I needed a 4 bar delivery rather than the 3 bar the later VR6 pump delivers. The pump is £129.98 inc VAT delivered.
 

The White Spy

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Had the day off and was able to spend some time under the hood. The closest thing I could think of to check the injectors without pulling the manifold and the rail was to let the car idle with the fuel pressure gauge on it then kill it and pinch the return line to see if the injectors hold pressure. It appears to me they don't but perhaps my logic is flawed? I would think that if the check valve was bad it would still hold pressure at the rail as long as the return line wasn't allowing fuel to flow back to the tank. Thoughts? I looked all over for external leaks but I don't see any nor is it dripping.
 
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