Help required to confirm tandem pump issues

[Richard75]

Hi all, this is my first post and yes I need some assistance.
I have a 2007 Passat TDI 170 SEL dsg which has recently developed a misfire around 3k rpm.
I looked into this with the help of the forum and think I know whats causing the issue--tandem pump.
Today ive changed the fuel filter and yes it looked more like a used oil filter than a fuel one!!
the concern I have is proving its the tandem pump.... I read so many threads/posts with conflicting information as to the cause
injector issues or tandem pump?

Question--is there any way of confirming the tandem pump is at fault before I part with £200 for a new one??

any advice gratefully received

[DMitch16]

Often it is the tandem pump gasket that is the issue rather than the rarer issue of failed internal seals within the pump. Correctly fitting the gasket to dry as possible surfaces of both pump and head plus correct torquing of all 3 bolts including the lower one obstructed by the coolant / egr pipe is crucial. Any new gasket must be perfect with absolutely no distortion or kinks which is sometimes difficult as parts monkeys shove them into tight polythene bags often bending them slightly which renders the gasket almost unusable.

There are also seal repair kits available at a fraction of the pump cost for the Bosch tandem pump if you are mechanically savvy and can generally perform seal changes.

It is possible that the injector seals have stiffened a bit but again not as common as a failed tandem pump gasket. The oil and diesel holes in the head are very close together under the pump and cross contamination issues very common.

I ran a whole £2 bottle of Redex Diesel cleaner through every 4th tank for a couple of months and changed the diesel filter after every 3000 miles which removed some of the oil from the fuel system but the only real way to get rid of the oil contamination is to clean the tank and flush all fuel lines.

[Richard75]

Thanks for the reply Mad Mitch.
I think im going to monitor the situation, although the car has full service history I cant be sure when it was last changed!
since changing it the car is driving a lot better, the misfire at 3k rpm has gone (although there is a slight judder/misfire around 4k rpm now)
I currently do about 2.5K miles a month so plan to change the filter then a see what state its in.