Intermittent starting issue

[skahigh]

Every now and then since I bought my van about 2 years ago I have had an issue where it fails to start, the engine turns over as normal but doesn't fire even if left turning over for several seconds.

When this happens, it usually happens repeatedly but if left for a few minutes will then start up. I have noticed that it seems to happen more often during cold weather and occurrences are clustered so, it will go weeks or months without happening and then happen on almost every start for a couple of days. Recently the occurrences seem to have become more frequent and mean I just can't trust the van.

I don't believe any fault codes are consistently logged relating to the issue since I happened to clear the codes one day, then immediately experience the issue and then rescanned with nothing logged.

I bought OBDeleven but found I couldn't get it to read most of the logging values mentioned in another thread so finally decided to stump up for a VCDS cable as I knew a garage would get nowhere without being able to replicate the problem.

Typically it was then faultless for a week or so until tonight leaving work when it happened so consistently that the battery got worn down to the point that the engine cranking revs were dropping quite severely and I figured I'd call the AA. An hour later and still no sign so I thought I'd give it one more go, even with a weak crank it then started up on the second go and I drove home with no problems.

Fortunately, I'd expected this and had the VCDS cable and a laptop in the van so managed to capture a few logs as recommended in another thread, I'm hoping someone with more knowledge than me might be able to advise where to start trying to diagnose the problem.

The fuel pressure never builds up but I've no idea where else to look.

TLDR version:

Van doesn't start, logs captured, fuel pressure problem(?), please help!

Apologies for the multiple logs, I tried it several times as I wasn't sure if I was capturing enough info in enough detail so tried multiple times. I've also attached a block map from last week when the van was starting.

Thanks in advance!!!

 

[Dellmassive]

@mmi

We have some logs for your expert analysis.

So are we saying it's a no start due to low fuel rail pressure?

 

[mmi]

fuel pressure problem(?)

Indeed, all the logs show essentially no fuel pressure buildup - should be around 30000 kPa - e.g shown here Won’t start [Resolved] However, when running (blockmap.csv) the fuel pressure is normal.

Then a bit mystery why air mass sensor reports non-zero when engine is off. Won't affect the fuel pressure though.



Does the fuel lift pump (in the tank) actually run? VCDS can test run the pump.
Ignition ON > VCDS > Engine > Output test > Fuel pump electronics
See details here:

Start up fault

Really happy with the help so far - have never received any remotely useful input from the dealership. But in there defence they never observed it faulting first hand only my videos. VCDS has been fantastic so far - only my inexperience limiting it. Reading the comments on the time stamps does...

www.t6forum.com

 

[skahigh]

Thanks very much, I've run the fuel electronics test and can hear the pump alternating on and off. It's a distinctive sound, can't say I've ever noticed it before, I assume it runs constantly when the engine is running? I'll keep an ear out for it next time it's cranking without start.

I guess the next time I get a non-start I should run that test again to confirm if the pump runs?

Are there multiple lift pumps or just one in the tank feeding the HPFP?

 

[skahigh]

I've just been looking at this thread, I'm guessing the wiring on the T6 is similar to the T5?

A thought occurs (possibly clutching at straws), at some point before my ownership the van was wet inside and there is surface corrosion on metalwork all over the interior. I'm wondering if there could be corrosion on the connector under the passenger seat causing the issue relating to temperature / humidity maybe??? While I was waiting for the AA man earlier I had my diesel heater on warming the interior.

Possible? Or Total nonsense?

 

[DXX]

Just the one lift pump in the fuel tank and there is a wiring loom connector under the passenger seat. It would be worth checking for corrosion, the contacts should be obvious but if it has tracked up the conductors it will be hard to tell without cutting.
While you’re in there I would check every connection.
As a VIP member you will find the wiring diagrams in the download section.

 

[Dellmassive]

there can be two fuel pumps . . . ( engine spec specific?)

both can / need to be driven from VCDS to prime the system.

v393 - supplementary pump




+++++++++++

lift pump in tank . . G6





++++++++++++++


main tank lift pump: ( all vans )









vans with sup` pump V393








van without sup` pump:





+++++++++++++

T6 & T6.1 - Diesel Fuel Supply System Workshop Manual

Workshop manual covering fuel supply system for all diesel engined vehicles This document covers removal/installation of system components like tank/pump/filters etc and also covers misfuelling procedures VIP Membership is required to download...

www.t6forum.com

++++++++++++++++++

 

[Dellmassive]

not sure what requirements set the second v393 pump.

but im sure my T30 T5.1 150 had the twin pump setup.

Run the van dry on diesel once.... Filled up with 5lt Jerry can, but wouldn't restart untill almost a flat battery..... Had to follow the workshop manual and drive both lift pumps alternate for a few mins before it would fire. (I never made that mistake again)

 

[skahigh]

Thanks again. Just had a look under the bonnet, no supplementary pump on mine!

Will pull the passenger seat out today and check on the status of the connections.

 

[skahigh]

Checked the connections under the passenger seat, no significant corrosion particularly visible but sprayed with ACF-50 and agitated anyway. Guess I just have to wait until it happens again.

 

[Dellmassive]

out of interest i just checked mine. . .


looks like i have the standard fuel filter, with no secondary pump.





and in VCDS i had only one lift fuel pump listed in the test menu,


i done some screenshots . . . . but they didnt save proper. . . :{




+++++++++++++++++



but from the VCDS menu you can run the lift pump.


you can then hear the pump humming.


i did a trace on the fuel pressures etc . . . but it didnt show much tbh.

 

[Dellmassive]

copying the same data set as @mmi


you can see that the Fuel lift pump is commanded ON @ 100% duty cycle


but the Rail Pressure doesn't rise.

 

[Dellmassive]

vs the 27200 value from a known good start . .

 

[mmi]

you can see that the Fuel lift pump is commanded ON @ 100% duty cycle


but the Rail Pressure doesn't rise.

Running lift pump (especially without cranking) is not enough to be seen at fuel rail pressure reading - thus need to be verified somehow differently.

Below a snippet of running output test and monitoring fuel pressure related values during the test. The lift pump pulsation seen on the rightmost column. No real change seen in the other values.

 

[skahigh]

Forgive my ignorance, would you expect the rail pressure to rise when the lift pump is activated? Or only when the HPFP kicks in?

Is there any logging that can be done to determine which of those two pumps might be at fault somehow? Other than listening for activation of the lift pump obviously.

 

[DXX]

Forgive my ignorance, would you expect the rail pressure to rise when the lift pump is activated? Or only when the HPFP kicks in?

Is there any logging that can be done to determine which of those two pumps might be at fault somehow? Other than listening for activation of the lift pump obviously.

I would say no.
Depending on the engine code the HPFP is either a single plunger or a tandem plunger pump and they don’t leak back otherwise rail pressure would be lost when the engine stops. I’m not sure if there is a NRV built into the pump discharge ports.
Also if the lift pump could pressurise the rail without the HPFP rotating then the fuel system could be bled at the injectors without cranking the engine. This is not the case.

 

[Dellmassive]

Forgive my ignorance, would you expect the rail pressure to rise when the lift pump is activated? Or only when the HPFP kicks in?

Is there any logging that can be done to determine which of those two pumps might be at fault somehow? Other than listening for activation of the lift pump obviously.

no,

rail pressure only rises when HPFP is running.

+++

one or two lift pumps can be run from a scan tool like VCDS or other.


+++


rail pressure does drop after engine shut down as @mmi shows on his diag report, (can you post a link back to that job?)

not sure what the pressure drop is controlled by. . . most likely the rail pressure control valve.



++++

 

[mmi]

would you expect the rail pressure to rise when the lift pump is activated?

No, actually can be seen in the post #14 - lift pump cycled but no rise in fuel pressure at rail.

Or only when the HPFP kicks in?

Correct - when engine is cranked and eventually running.
E.g. here:

Start up fault

Hi again, I'm trying to record my van when in fault with my new VCDS. I think the attached might show the fault? The problem is the fault doesn't present every start up. Once when I was trying to record it the VCDS just displayed n/a in every column. I've ticked the boxes that delmassive...

www.t6forum.com

rail pressure does drop after engine shut down as @mmi shows on his diag report, (can you post a link back to that job?)

Here you go:

Start up fault

Hi again, I'm trying to record my van when in fault with my new VCDS. I think the attached might show the fault? The problem is the fault doesn't present every start up. Once when I was trying to record it the VCDS just displayed n/a in every column. I've ticked the boxes that delmassive...

www.t6forum.com

 

[skahigh]

No, actually can be seen in the post #14 - lift pump cycled but no rise in fuel pressure at rail.

I thought it was unlikely but, this just means the logs don't point anywhere in particular. Frustrating having to wait for it to happen again just to test the lift pump activation.

Let's assume that the lift pump is activating, what would be the next place to look? Is the HPFP electrically activated/monitored at all or is it entirely mechanical?

 

[DXX]

I thought it was unlikely but, this just means the logs don't point anywhere in particular. Frustrating having to wait for it to happen again just to test the lift pump activation.

Let's assume that the lift pump is activating, what would be the next place to look? Is the HPFP electrically activated/monitored at all or is it entirely mechanical?

The only electrical connection to the HPFP is the fuel metering valve N290