270 CDI (om612) hpfp failure opinions? W209 CLK

[smanderson117]

That's odd, I just bought the 3 low pressure fuel lines for the same 270cdi from mercedes last week and the all arrived next day

Must've got the last ones got the one from fuel filter to LP pump, the weird one that goes between HP and LP pump with the tee off for pressure test point one. Just the one from HPFP to the regulator/fuel rail I had to get aftermarket. Hoping this fixed my issue, otherwise it's LPFP or finally injectors. Nearly replaced full system

 

[smanderson117]

@mersum1es hoping for your opinion here please!
Changed all low pressure fuel lines so:

• Fuel filter to low pressure fuel pump (genuine merc)
• Low pressure pump to HPFP (with the tee off for the test point thing) (genuine part)
• HPFP to fuel rail at pressure valve end (Gates branded part, NLA from merc)

I smeared a thin layer of grease on o rings as they were dry and to help sealing and prevent tears. Installation went fine after figuring out routing again. All seemed well but then after shut off, still takes a while cranking. Also cut out and gave same code as previous, only when you're really on it (foot flat to the floor and towards top end of revs only) and seems to be same point in rev range most times.
Will then shut off, start up again with long crank and runs fine if you only half throttle everywhere so I can pootle about.

The videos below show what I believe to be air in the lines? First video is from fuel filter to LP pump, second is between LP pump and HPFP. Line to the rail seems fine can't see any bubbles there. How am I still having air in the system?! Fuel filter is new 1k miles/2 months ago and is Mann item. Any ideas as I am stumped!!!

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[mersum1es]

well, definitely bubbles is reason to your problems, but what is causing bubbles...

W203 has infamous tank line connection which corrode and brittle in time, not sure what king of system CLK has. Take a bucket of fuel, put filter incoming line to bucket and test.

If you are still getting bubbles, they are inborn somewhere engine bay, travelling to filter and spreading to system. Few things come to my mind, remember one case when broken injector tank line t-piece caused that, then rarely pressure relief valve 0-ring can be damaged but you should see bubbles from rail to return then.

Have you now changed ALL low pressure lines AND put new o-ring, plus clipped them tightly?

 

[smanderson117]

well, definitely bubbles is reason to your problems, but what is causing bubbles...

W203 has infamous tank line connection which corrode and brittle in time, not sure what king of system CLK has. Take a bucket of fuel, put filter incoming line to bucket and test.

If you are still getting bubbles, they are inborn somewhere engine bay, travelling to filter and spreading to system. Few things come to my mind, remember one case when broken injector tank line t-piece caused that, then rarely pressure relief valve 0-ring can be damaged but you should see bubbles from rail to return then.

Have you now changed ALL low pressure lines AND put new o-ring, plus clipped them tightly?

Ah ok, so maybe a can of fuel with a hose connected to the fuel filter and see if it gets bubbles drawing from that? Then If not, I know it's somewhere along that long fuel line to the tank? I get you

Which part do you mean by injector tank line t-piece sorry, the fuel return connector things on top of the injector?

Pressure relief valve as in pressure regulator? That should be good as I have changed that but yes no bubbles in the rail return line I can see oddly.

Yes all 3 lines are brand new (2 genuine 1 aftermarket) and they came with new o-rings. I could see old o rings were very worn and flat so thought this would fix it but I guess not! All connections are on tightly I have checked by tugging etc and they are all seated all the way

Thanks!

 

[smanderson117]

Just been back out to check something, noticed what I have found to be the fuel pre heater connections not looking great, will chop the end off this and use some of the slack to give a good new surface and secure with a new normal jubilee clip, perhaps it's JUST taking in a tiny bit of air from there hence why it still starts etc.
The annoying thing is that it was cutting out under load as it is now, but not long cranking (would fire up fine) before I changed HPFP, so not sure if just a coincidence or maybe something amiss there I don't know. But for sure, the bubbles are no good so must eliminate those regardless

 

[smanderson117]

Well, changed that and it seems to no longer cut out and no more bubbles! Going to really give it some later tonight when roads are dead to confirm no longer cutting out. It is still cranking forever though haha!

I want to change my o-ring on the LP pump both the one behind the unit and behind the cover. I have a part number for the one that seals the unit itself, hwoever I can't seem to find anything for the one that is there when you take off the cover of the low pressure pump. Anyone have any ideas? It seems to be common for this to flatten off as per screnshot from someonse video below:

 

[mersum1es]

Good that one part of the problem is solved.

Aux pump rarely fails and their seals, even flat and hard, can keep air out unless some goes and opens them

I believe you can measure diameter and thickness of the o-ring, and just buy universal one (material fit for fuel of course). Good thing of o-ring is that it is not very sensitive to dimensions, as far as thickness of ring is on + side (they goes standard steps) and you don't need to seal pressure over 200 bar...