T6 Wouldn't Start

[Tourershine]

I've had a dig around, but couldn't find anything that was similar.

I've just got home after 2 weeks away in my Motorhome. The first thing I tend to do, is check all the vehicles that have been sat for a few weeks.
Low and behold the van wouldn't start. I had the exact same last time I went on holiday and left it sat for a longish period.

Key in, ignition on for couple of seconds, and it fires up, but runs really rough on 3 cylinders.
Turn off, start again, and the same.
Turn off, try to start and it's just spins over.
Try few mins later and it starts, but still a little rough on tick over, so leave running for a few mins untouched and eventually it seems to clear.

No smoke, no engine lights, no warnings.

I'd say it's because it's been sat, but really... ? It's a 2017 modern diesel, not an old banger.
It's due another service, but I know if I mention this to VW, they won't find anything, because there's nothing for them to find.

Any thoughts?

 

[Dellmassive]

sounds like low fuel rail pressure and airlock . . . ?

possibly the fuel in the rail has bled down and the priming pump and HPFP is trying to building up rail pressure . . . . . . possibly purging any air out the system, on that first re-start.

must admit not had this myself before . . . . . normally just a flat battery after a couple of weeks.

might be worth mentioning to the dealers as they may have seen similar for other vans sitting around on the lot for ages or new vans being delivered that haven't been run for a long time.

***********

Key in, ignition on for couple of seconds, and it fires up, but runs really rough on 3 cylinders. - (remaining fuel in rail + HPFP)
Turn off, start again, and the same. - (remaining fuel in rail + HPFP - system starting to repressurise + purge)
Turn off, try to start and it's just spins over. - (rail + lines out of fuel + airlocked? awaiting fresh fuel for HPFP to fill rail)
Try few mins later and it starts, but still a little rough on tick over, so leave running for a few mins untouched and eventually it seems to clear. - (HPFP clearing air out of HP line and rail/injectors)

************

a possible check return valve faulty? allowing rail pressure to drop and bleed back down to tank causing an air lock and needing purging on restart?

There is a test they can do by monitoring the rail pressure:

Running pressure: as per spec
rest after run: pressure should increase due to heat soak, then drop and remain at rest.
rest over night / after 24hrs: bleeddown, pressure shouold remain to spec and not drop too much.

 

[Tourershine]

sounds like low fuel rail pressure and airlock . . . ?

possibly the fuel in the rail has bled down and the priming pump and HPFP is trying to building up rail pressure . . . . . . possibly purging any air out the system, on that first re-start.

must admit not had this myself before . . . . . normally just a flat battery after a couple of weeks.

might be worth mentioning to the dealers as they may have seen similar for other vans sitting around on the lot for ages or new vans being delivered that haven't been run for a long time.

***********

Key in, ignition on for couple of seconds, and it fires up, but runs really rough on 3 cylinders. - (remaining fuel in rail + HPFP)
Turn off, start again, and the same. - (remaining fuel in rail + HPFP - system starting to repressurise + purge)
Turn off, try to start and it's just spins over. - (rail + lines out of fuel + airlocked? awaiting fresh fuel for HPFP to fill rail)
Try few mins later and it starts, but still a little rough on tick over, so leave running for a few mins untouched and eventually it seems to clear. - (HPFP clearing air out of HP line and rail/injectors)

************

a possible check return valve faulty? allowing rail pressure to drop and bleed back down to tank causing an air lock and needing purging on restart?

There is a test they can do by monitoring the rail pressure:

Running pressure: as per spec
rest after run: pressure should increase due to heat soak, then drop and remain at rest.
rest over night / after 24hrs: bleeddown, pressure shouold remain to spec and not drop too much.

Thanks mate. I knew when you popped up as on line, you'd be drawn straight to my issue Captain McSpanner

I will mention it to the tech and see if they can run a test.

 

[Dellmassive]

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[Dellmassive]

* FYI

pressure loss could be due to:
leaking return valve,
Leaking injector,
Leaking HPFP.
Leaking HP fuel reg valve.

#11 The pressure retention valve has the task of always maintaining a residual pressure (control volume) of
approx. 10 bar in the fuel return lines. The injectors require this control volume to function

 

[mmi]

T6 TDI Fuel System Lesson #2 - Injectors:

Our Self Study Programme 564 "The 2.0 litre TDI engine in the T6" on page 25 about injector working principles refers to SSP 465 "The 1.2L 3-cylinder TDI Engine with Common Rail Fuel Injection System" for more details - starting there on page 27. Also is described how fuel filter pre-heating is implemented (page 37).
Enjoy ---> 1.2L 3-cylinder TDI Engine | SSP 465 Online | Free Download

 

[Lord Mfwic]

I frequently run a hire van for work and I've had the same problem and symptoms when I have left mine standing for a few weeks. I've not mentioned it to VW as I just put it down to the fact it had been stood for so long.
No help I know but at least its not just your van.

 

[rover220]

I've had a dig around, but couldn't find anything that was similar.

I've just got home after 2 weeks away in my Motorhome. The first thing I tend to do, is check all the vehicles that have been sat for a few weeks.
Low and behold the van wouldn't start. I had the exact same last time I went on holiday and left it sat for a longish period.

Key in, ignition on for couple of seconds, and it fires up, but runs really rough on 3 cylinders.
Turn off, start again, and the same.
Turn off, try to start and it's just spins over.
Try few mins later and it starts, but still a little rough on tick over, so leave running for a few mins untouched and eventually it seems to clear.

No smoke, no engine lights, no warnings.

I'd say it's because it's been sat, but really... ? It's a 2017 modern diesel, not an old banger.
It's due another service, but I know if I mention this to VW, they won't find anything, because there's nothing for them to find.

Any thoughts?

my old works t6 used to do exactly this if it was left for a long weekend, never got to the bottom of the problem though.

 

[Tourershine]

Thanks for all the replies, it's less worrying to know it's not an unusual issue.
The van has been left for several days without an issue, it only seems to be when I go on holiday for a couple of weeks.

 

[ei-aprilia]

Thanks for all the replies, it's less worrying to know it's not an unusual issue.
The van has been left for several days without an issue, it only seems to be when I go on holiday for a couple of weeks.

I'm sure it says in the manual you must disconnect the battery if the van is going to be left idle for any length of time. I wonder if it's related to that?

 

[Tourershine]

Just popped the Carista on, and got these results. Some if them might of been from a while back, but I've reset them and will see if anything pops up again.

 

[Dellmassive]

disconnecting the battery shouldn't be necessary for only a couple weeks.

those stored codes above dont seem to be related,

im sticking with the rail pressure bleeding down after a couple of weeks, mention it to the dealer and let us know what they say . . . . . . . .

(it would be interesting to see if a "VCDS fuel pump prime" procedure would stop the issue . . . . ie re-prime the fuel system before the first start after a 2week rest. To then see if the van starts first time without any rough running)

 

[Loz]

If the lift pump primes for a few seconds every time you open the driver's door, so maybe repeat that a few time before starting..

 

[Tourershine]

If the lift pump primes for a few seconds every time you open the driver's door, so maybe repeat that a few time before starting..

I'm away again at the end of May, so I will try out these things upon my return, but I'm going to film it starting, so I have something to show VW. We all know what they are like, if it's not showing a light or obvious, they wont throw too much effort into finding the problem..

 

[Dilbert]

If the lift pump primes for a few seconds every time you open the driver's door,

That is very interesting. I had a lumpy engine experience with a short loss of power after we set off from being parked at our daughters. We were parked up for 6 days tight to a fence so I got back in using the passenger door and the drivers door was not opened. I am now wondering if this was the cause....

 

[oldiebut goodie]

I am going to have to bear this in mind as I rarely open the driver's door on my vans - saves swinging a big door out into traffic and you step straight onto the pavement. Have been doing this for years and years!

 

[mmi]

I'm going to put a bet on injectors.

 

[Stay Frosty]

If it was a leaking injector wouldn't you get a bit of a white plume from the exhaust during the initial lumpy running and no smoke if it was fuel starvation from an emptied fuel rail?

 

[mmi]

I'm going to put a bet on injectors.

My thought is that the injectors are not "leaking" (into cylinders) - just the oppposite: the intended fuel just doesn't get injected into cylinders which then can be detected as back flow into fuel filter (through "11" in the picture above). Similarities as in a test ---> Injector failure

 

[Dellmassive]

@Tourershine

So here i am, back after a 2week break on a family holiday.

The van has been sitting idle for the whole time . . . . . . . a good test to see what happens on the restart.

the standing battery voltage was 12.1v according to the Tacker, which dropped to 11.6v with the ignition on.

I managed to get it on video for you . . . . . . It fired up on the first turn . . . . . . but cut out due to me forgetting to put in the immobilizer code

but then restarted again with no issues . . . . . . so i think your bus may be loosing rail fuel pressure causing the poor start after your holiday.

this one started on the button.

.