Thread: Suspected HPFP belt issue

ok. It looks like I have posted without researching properly. I see Bananas has gone through this whole thing. I have read through the entire thread. What a wild ride. It gives me confidence to have a go at replacing the HPFP.

Not sure what to do with this post from this point (perhaps close or merge with Bananas)?

2011 D4 'Gearbox Fault' warning

If that were me, I would have changed the fuel rail sensor as you have, I've not seen that particular fault before.

If that didn't work, yep... Onto the HPFP.

It's not actually that bad a job, but it is not for beginners.

Was the sensor genuine or aftermarket ? I've heard of issues with non genuine pressure sensors.

You know, I know, we all know, it’s the pump. Sorry to be the bearer of bad news.

Originally Posted by ibuysingleusetools

The image below is a snapshot of the problem occurring. The fuel pressure takes a little while to follow the volume control valve but it's not too different from when it runs normally. There doesn't appear to be any reason for the valve pressure to jump as the car doesn't appear to be changing gear (it's a constant speed and throttle).

This is pretty much how it manifests. The PCV sticks. So you are cruising along and relatively low load, you maybe hit a strong headwind or an imperceptibly small incline and the car wants a smidgen more power so it tries to open up the PCV. It notices the pressure hasn't increased, so it tries to open it a bit more. This leads to a rapid feedback loop that pegs the PCV command signal (in reality somewhere around 50%). It sits there for ~2 seconds without the rail pressure increasing and triggers the fault. I could cycle the ignition on the road and reset the fault.

I set a trigger in the GAP to cause an alarm when the PCV pegged and provided I got off the throttle (or cancelled the cruise control) when the alarm went off I could unstick it by releasing then nailing the throttle. If you can get the load request off the engine prior to the 2 second timer expiring it won't trigger the fault. I found that *large* valve requests always worked. So throttle stabs would unstick it for a while. I also tried manually exercising the valve externally (essentially a battery and a bit of current limiting) brought me a couple of weeks relief each time.

As others have already said, it's highly likely you need a new pump.