All Things Mk5 > How to Guides / Troubleshooting

One reason why fuel-rail pressure may be low....

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ROH ECHT:
I found the pic below and cleaned up the specs to be more legible. Hoping for confirmation on the dimensions as well. I will leave it posted for future use when others are struggling to find why the rail pressure is suffering. As this may be the reason for it...given the age of our MK5 today.

This pic is supposedly of the intake cam tri-lobe; found on std-K03/BPY (and the like; AXX_BWA_etc.) of the EA113 engine. Remember, or know, what is important to produce rail pressure is the cam lift...in other words; the travel/stroke of the piston inside the HPFP.

As we know, the K04 equipped cars have intake cams with a bit more cam lift on the tri-lobe.

Also, take a look and if you can confirm the specs in the pic, just comment below please.

breeze:
I have started to look at the cam lobe, follower and even the HPFP plunger tip on these cars as wear items.

On my car, rail pressure was perfect when standard but when running a stage one map it was possible to get rail pressure dropping briefly in 4th gear under very particular conditions. IIRC around 3.5k at full throttle. Very rarely it would log a fault code too. Felt like the kind of thing I would have ignored without logging.

When I disassembled I found wear on the lobe, follower and plunger. Not a massive amount and at 145k I am sure would have been fine indefinitely with the standard map.

Classic dealer solution is to renew everything with standard parts. Partly because the I am thinking about future upgrades, I chose to do Autotech HPFP internals and a new follower to see whether that would be enough. Cam replacement is a much more complex and more time consuming job. Result was fuel pressure is now perfect, under all conditions.

I think we will all have wear at different stages across lobe, follower and plunger in these cars, but I’d say your lobe would need to be very worn if you have issues with new HPFP internals and follower.

ROH ECHT:
This all is likely only going to be helpful to those who've picked up their MK5 second, third, or fourth hand. Where the previous owner/s neglected all this, as well as informing the next owner. I've recently been helping a few with the issue. They've replaced all they could think of, only to find out the intake cam needed replacing. When they measured the tri-lobe 42.5mm, theirs was between 1.5mm to 2mm shy. There wasn't as much wear at the 3.5mm spot, so it was all worn at the peaks...thus reducing the cam lift and stroke of the HPFP's piston.

I thought if I posted this pic, perhaps some would then see it come up on one of their searches. And perhaps they would check the tri-lobe before replacing a list of fueling parts.

breeze:
Understood, yes it is good information to share.

My understanding was that the earlier intake cams were very prone to early wear but they were revised during production of the BWA. My car as a 2006 has an early cam. At 145k I thought a little wear was OK. I was looking at replacing the intake but in the end didn’t need it. You actually responded to one of my messages on the ‘tex.  :smiley:

As an aside, there is a way of replacing the intake cam without touching the cambelt or exhaust cam. That simplifies things massively, particularly if you have a recent cambelt and the adjuster performance is in spec. That was my backup plan.

https://www.audizine.com/forum/showthread.php/572832-2-0T-Intake-Cam-replacement

rich83:
Great info. Shame it’s impossible to measure without stripping the chain cover.

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