Intermittent Long Crank (randomly once/twice a day)

[mmi]

Could I ask what you mean by “centralised” no start please?

Sorry. I meant that the ECU commands always all injectors to fire as soon as all necessary conditions (cranking speed, timing, fuel pressure, etc) are fulfilled. Thus "centralised" = some of the conditions are not yet fulfilled causing ECU to hold back firing injectors - e.g. too slowly rising fuel pressure would hold injector firing until the pressure is high enough (for successful engine start).

So my thought is if engine starts up right on all cylinders it's not likely to be injector related. In other words - a leaking injector would cause engine to start (too early but) only on that cylinder, or failing injector would run poorly thus causing "rough" idling.

I hope this helps...

 

[PearShaped]

Sorry. I meant that the ECU commands always all injectors to fire as soon as all necessary conditions (cranking speed, timing, fuel pressure, etc) are fulfilled. Thus "centralised" = some of the conditions are not yet fulfilled causing ECU to hold back firing injectors - e.g. too slowly rising fuel pressure would hold injector firing until the pressure is high enough (for successful engine start).

So my thought is if engine starts up right on all cylinders it's not likely to be injector related. In other words - a leaking injector would cause engine to start (too early but) only on that cylinder, or failing injector would run poorly thus causing "rough" idling.

I hope this helps...

 

[PearShaped]

Sorry. I meant that the ECU commands always all injectors to fire as soon as all necessary conditions (cranking speed, timing, fuel pressure, etc) are fulfilled. Thus "centralised" = some of the conditions are not yet fulfilled causing ECU to hold back firing injectors - e.g. too slowly rising fuel pressure would hold injector firing until the pressure is high enough (for successful engine start).

So my thought is if engine starts up right on all cylinders it's not likely to be injector related. In other words - a leaking injector would cause engine to start (too early but) only on that cylinder, or failing injector would run poorly thus causing "rough" idling.

I hope this helps...

Hi mmi hope all is well. Here are 2 comparison videos as requested. I appreciate that the long crank isn't too long (it's longer sometimes), but hopefully this helps with the diagnostic. If it's early normal for this to happen, please excuse my ignorance, it just doesn't feel right when it happens if that makes sense.

Long crank: https://www.youtube.com/shorts/Oo3lgg5JrA4
Standard crank: https://www.youtube.com/shorts/MbXSfpajxMw

Thanks again

 

[Chewywms]

Hi mmi hope all is well. Here are 2 comparison videos as requested. I appreciate that the long crank isn't too long (it's longer sometimes), but hopefully this helps with the diagnostic. If it's early normal for this to happen, please excuse my ignorance, it just doesn't feel right when it happens if that makes sense.

Long crank:

Standard crank:

Thanks again

Hi mate,

Just wondering if you got any further with the intermittent cranking issue? I also have a similar situation- which appears only to happen after driving a short journey (few hundred meters at my mums house) leaving the van 5-10 mins before re starting the van.

Thanks

 

[PearShaped]

Hi mate,

Just wondering if you got any further with the intermittent cranking issue? I also have a similar situation- which appears only to happen after driving a short journey (few hundred meters at my mums house) leaving the van 5-10 mins before re starting the van.

Thanks

Hi mate. I changed the fuel filter recently, and at the same time I did the cambelt (as it was due anyway)… I didn’t think this would make a difference, and no change.

The mechanic also plugged it in and no codes… They're vw specialists and said it’s highly likely going to be one of the injectors, but to pull the injectors out can be costly and I'd be without the van for a week as they need to send them off etc. They suggested waiting to see if the issue gets worse, and if so, it would be easier to diagnose and fix.

It's still happening once a day, but in general it's the same as it was a month ago. It's frustrating, but the way I'm looking at it is it's going to be a little issue somewhere that eventually will get sorted, but for now, it's just a minor inconvenience. I'll deffo update when I eventually get it sorted bud.

 

[mmi]

Hi mmi hope all is well. Here are 2 comparison videos as requested. I appreciate that the long crank isn't too long (it's longer sometimes), but hopefully this helps with the diagnostic. If it's early normal for this to happen, please excuse my ignorance, it just doesn't feel right when it happens if that makes sense.

Long crank:

Standard crank:

Thanks again

Apologies @PearShaped - I somehow managed to miss your post and videos.

I noticed that the ignition was turned on for about 6½ seconds before cranking was started.
Have you tried if it makes any difference by cranking the engine right away (do not wait dash lights to turn off etc.? You might actually notice a slight delay before cranking starts because ECU holds back cranking till glow plugs have done their job.

ECU turns on glow plugs immediately when ignition is switched on - but only for a second (or even less) (at 13 °C video) so waiting without cranking actually let's the plugs to cool down

 

[PearShaped]

Apologies @PearShaped - I somehow managed to miss your post and videos.

I noticed that the ignition was turned on for about 6½ seconds before cranking was started.
Have you tried if it makes any difference by cranking the engine right away (do not wait dash lights to turn off etc.? You might actually notice a slight delay before cranking starts because ECU holds back carnking till glow plugs have done their job.

ECU turns on glow plugs immediately when ignition is switched on - but only for a second (or even less) (at 13 °C video) so waiting without cranking actually let's the plugs to cool down

Hi mmi, thanks for coming back to me, greatly appreciated. Interesting enough I tried your suggestion this morning and it actually made it worse… but that could be a good thing to diagnose? I cranked straight away and there was a slight delay as you suggested, but the crank was long. I stopped the van to load the tools on and tried it again (same immediate crank) and the crank was long again. Normally I’m the morning I wait for a few second until all lights go out and I hear the electrics start. Cheers, Seb

 

[mmi]

Another thing to try would be to start:

Turn ignition on for the usual 5-6 seconds, then turn ignition off, and then try cranking straight away.

However, I'm not expecting to be different - thus a kind of excluding glow plug circuitry - although at current temperatures the glow plugs don't do much anyways. And, if detected faulty they would throw an emission warning light on dash.

It’s in for a cambelt change on the 28th

The new belt didn't change the behaviour?

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Below a few examples how VCDS diagnostic tool could be used to further diagnose the issue:

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