T6 150 long cold crank time - help required please!

[Gaffa]

Ever since I bought my T6 18 months ago, on a "cold" start (in the morning or after work), it'll take a few seconds to start up. The crank speed is high and healthy and the situation is the same regardless of the amount of fuel in the tank.

The battery has just been replaced and coded just in case.
I've also replaced the lift pump with a Bosch part from Parts In Motion (same as genuine, stickers and markings match up to the VWAG one I took out).
Changing these 2 parts made no difference.

I've done a lot of reading on here and I'm not sure whether it's timing or fuel delivery related. I have genuine VCDS and have followed the guides for obtaining data for engine off, cold crank and engine running. I have attached these below.

If anyone is able to decipher the data and help me out, I'd really appreciate it.

Thanks!

 

[manfrotto]

Does it start cranking straight away after turning key, or is there a delay before it starts cranking?
Blockmap is showing a 2.5 second pre-glow time before starting - this would normally mean that the van wouldn't even start cranking until then (and would show on dashboard light. If you leave the ignition on until the pre-glow is finished, does it start pretty much straight away then?

 

[Gaffa]

I'm old skool, I always wait for the glow plug light to go out before turning the key. No warning lights on dash, only permanent code is open circuit to heated rear window.

 

[manfrotto]

I'm old skool, I always wait for the glow plug light to go out before turning the key. No warning lights on dash, only permanent code is open circuit to heated rear window.

Ah, I think I saw that on the first file you posted with the live data during startup.
I'm sure @mmi will be along shortly with his expert opinion from the data you have posted.

 

[Gaffa]

I had the ignition on for a minute or so while setting up VCDS so maybe the glow plugs turned on again when I turned the key to start. I can redo the tests if required, I can also do the tests with a "warm" engine if it helps.

 

[mmi]

Obvious reason for long crank is that it takes extremely long to build enough fuel pressure for ECU to fire injectors.

See below:

at 4.24 seconds cranking starts​

at 6.34 seconds ECU fires injectors as fuel pressure has reached threshold​

at 6.50 seconds fuel pressure has reached normal level (about 300 bars)​

at 6.68 engine runs​

Normally pressure build-up takes less than 0.4 seconds (from cranking start).
Prime suspect is the high pressure fuel pump. Perhaps just a snapped spring in the HPFP

Engine cut out and wont start now.

Here is where we are at for some reason we can not clear the fault code P056200 System Voltage Low Voltage That indicates that something is still wrong. Couuld this be the reason why it's not starting, that the ECU is not getting enough power or thinks its not getting enough voltage even...

www.t6forum.com

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EDIT: Plots



For comparison a normal pressure build-up

https://www.t6forum.com/threads/tra...clicking-under-acceleration.64716/post-832367

 

[Gaffa]

Thank you @mmi , I appreciate your help with this. Looks like pump spring is now shrouded in plastic on the DFP6.1 pump so that option's out. The quote I received today to replace the pump, timing belt and crank seal was in excess of £2000, and I doubt that included all the work required to flush the system out, check injectors, change rubbers etc etc. Buying a T6 was a huge mistake, it's been a money pit since the day I bought it and it's only going to get worse isn't it. The juice ain't worth the squeeze anymore. My T5.1 had 208k on the clock and only needed a clutch release bearing and EGR cooler in 12 years.

 

[Gaffa]

Update on this, I took it to a local garage for investigation and they've called with good news. They've changed the filter, primed the system several times and they say it starts up nice now. I'll collect it on Monday and see how it goes!

 

[mmi]

Update on this, I took it to a local garage for investigation and they've called with good news. They've changed the filter, primed the system several times and they say it starts up nice now. I'll collect it on Monday and see how it goes!

Sounds promising

Please make a log of the following when starting. Would be a good future reference if any problems arise later.

For tracing fuel pressure regulation circuitry:

IDE00021 Engine speed​

IDE00347 Air mass: actual value:​

IDE00352 Main injection: duration of activation​

IDE00407 Rail pressure regulation: status
IDE01378 Fuel high pressure: control deviation​

IDE05632 Fuel pressure regulator valve actual value​

IDE05633 Valve for fuel metering: feedback value measured​

IDE07807 Fuel temperature sensor 1: B1: raw value​

IDE07818 Fuel high pressure sensor: actual value​

IDE07819 Fuel high pressure sensor: unconditioned voltage​

IDE07821 Fuel metering valve: activation​

IDE07822 Fuel pressure regulator valve: activation​

 

[DXX]

Update on this, I took it to a local garage for investigation and they've called with good news. They've changed the filter, primed the system several times and they say it starts up nice now. I'll collect it on Monday and see how it goes!

@TAB-TEC How many miles had the fuel filter done?