MK5 Golf GTI

All Things Mk5 => Mk5 General Area => Topic started by: Dunkdafunk on July 27, 2020, 05:14:21 pm

Title: HPFP what isit that fails?
Post by: Dunkdafunk on July 27, 2020, 05:14:21 pm

Golf mk5 BWA. Hitachi 2:2 hpfp.

What isit that typically fails on the hpfp? Top sensor or piston?

Bit of a story here. But it might help someone, so this is why I'm asking...

Last few months I've been gettin low pressure fuel faults outside of specification, so naturally i took a closer look at the lpfp with vag block 103 and 106. Went for a few drives, noticed on occasion alot of vaccum in the petrol tank. Also had some white oil gunk over the winter aswell. Worked out it was the thermostat not holding 90deg, so the evap system didn't work properly. I then thought the lpfp could be knackered because of the strong vaccum in the tank, and noticed its duty cycle often at 95%.

Ready to buy a ttrs pump. Then the car just simply cut out a few days ago, and I reset the trims via battery pull which got it started again. Codes were low pressure outside spec. Low fuel rail pressure.

So I was ready to buy a new lpfp, when I logged block 230. Noticed the hpfp actual and specified had some lag and there was a huge lag uphills in WOT. Took a closer look at the lpfp, and noticed one of the plastic plug pins was somewhat melted. Changed the lpfp (oem) and logged block 231, both low specificied and actual matched. But i went back to 230 and noticed my hpfp wasn't quite keeping up actual vs specified. So i changed the hpfp, and it works really well, the lpfp duty cycle is low, the lpfp sits really well. So it seems the lpfp was overworked due to the hpfp requesting more.

So im just wanting to know what isit that normally fails on the hpfp to cause the lag.

Title: Re: HPFP what isit that fails?
Post by: colesey on July 27, 2020, 06:22:59 pm

There is another known issue on the hpfp which is that the rubber shaft seal perishes and leaks fuel into the oil. Whilst I’m not suggesting that this is your issue, it may be something to check at some stage.

Title: Re: HPFP what isit that fails?
Post by: pudding on July 31, 2020, 03:14:23 pm

Yep, that and ground down shafts from follower failure are the most common failures. Less common is people breaking the sensor when removing/refitting the engine cover.

A badly leaking hpfp seal will make the engine oil stink of neat fuel, and increase the oil level.