If the tank is over 3/8 full it will not be siphon related. I would get a measure of fuel pressure at the rail and make sure it's rock stable. It should not change other than maybe 1/2 to maybe 1 psi drop when you punch the throttle.

New ≠ fixed you could always have a bad new part but over pressure at the pump will just mean more fuel back to the left tank.

A constant rich situation usually means MAF sending a bad signal or possibly bad O₂ reporting incorrectly but you will usually see mismatch of banks in that case.

When FPR goes bad as [mention]80stech [/mention] mentioned it's very unlikely to over pressure but if the symptoms match you need to confirm/rule out that possibility.

There's a vent hose from the FPR which looks like typical FPR that is used to compensate for vacuum at the intake but I've come to understand it's just a vent in case of diaphragm failure that will suck fuel/vapor to the intake.

That condition should lead to rich running : both from gas getting into the vent but also if it takes more pressure too open the valve because the diaphragm is letting fuel through.

So back to basics: you need to measure the fuel pressure. It should be 50 ±1 but rock stable. When wife's FPR had a failed o-ring the pressure bounced with each injector pulse.

The symptom she had was occasional very hard starts.

The worst case was the last drive to the shop to fix: took about 50 seconds of total cranking.


–awr–

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)