MurrayA4

Yeah always keep in mind that the genius of the 3.0L Tdi is the fueling system.It's why our vehicles are quiet and extraordinarily powerful and efficient - keep away Epa. Treat your whole system with great respect, good fuel and clean filters are critical ! We're talking 28,000 psi.out of the HPFP, tolerances are Germanic and one fat molecule of crap and bang.A little bit of overstatement but not that much.

brutus23079

If the fuel system sucks air (as mentioned above), the resulting lack of resistance (air vs liquid) can cause the spinning parts to literally fly apart into A LOT of little pieces, traveling downstream and destroying everything they touch. Doesn't mean it will happen, but it did happen to someone the day I took delivery. I was briefed about it when I asked about doing DIY maintenance. Dealer said cost to repair roughly $7000. That said, at 59,000 miles, I've changed three fuel filters without issue. You can hear the filter fill up using a VCDS. Without VCDS, you can end up like the guy who got clocked for thousands of dollars at 15,000 miles. And yeah, forget trying to claim warranty. Lol...

BarryT

i didn't pay much attention to it. I changed mine at 25k because I didn't know if it had been changed by the previous owner at 15k miles. The filter was about $30 if I remember correctly. I purchased the cabin filter, air filter, oil filter and fuel filter all at the same time so I can't remember. It's at 37k now so I'll change it again at 45k.

a1sailor

"With VCDS, you can energize the fuel pump without running the engine. This fills the empty fuel filter canister and doesn't run the HPFP without fuel. "

I see the need to prime the fuel filter after replacing using the VCDS, where does the air in the new filter get evacuated from the new filter if the pump is pushing fuel through the line?
How does the air get past the HPFP?
Thanks
Newbie to the vehicle and the Forum

tisi_03

You're filling the fuel filter and the air is cycling back into the fuel tank. It never gets to the HPFP unless you try and start it before purging the air out of the filter. DO NOT TRY TO START THE VEHICLE WITHOUT FIRST PURGING THE AIR OUT OF THE FUEL FILTER!! The VCDS will allow you to do this. I just did mine for the fourth time and the program is constantly changing but I believe it's the ENGINE block, Measuring Blocks/Basic Settings and then choose IDE00459 Transfer Fuel Pump (FP) test then GO. You will here the filter fill as the pump runs. Allow to run for one minute before stopping, then check for leaks and you're good to go.

motoguy128

Something easily forgotten, that with a diesel, the fuel system essentially replaces the spark plugs and throttle found on a gasoline engine. There are throttle bodies to manage airflow, but it's not metered like in a gasoline engine.

The ONLY thing that controls engine output is the amount of fuel sent to the engine. The compression ignites it and engine simply draws in however much air it gets. It's really cool how simple it is. The complexity is the emissions controls and precise fuel controls. But you could in theory rip all the modern stuff off and it would run just fine with 1890's low pressure pump fueling technology on it. Just generate a little more soot or Nox.

a1sailor

Thanks tisi.

tisi_03

a1, you're welcome. The first time you do it you're on pins and needles but the air purges out really fast. You'll hear the pump noise change after the filter is full and the air is out of the system. I run it a minute to make sure. It's real simple.

hoppster

Apologies for being a bit late to the game, recently became an owner of a 2014 Q5 3.0L TDI, looking to invest in a VCDS from Ross-Tech, and in need of completing a fuel filter replacement @ 35k miles...

Do you need to do any priming/diagnostics before removing the old filter, or just need to connect VCDS after the new filter is installed & then prime?

Thank you to all for contributing! Incredibly helpful

TomReed

Just new filter and prime.