Mk III vrs engine cutting out while driving

[Guyzer]

Hi all, For those who enjoy a detective mystery, I'm hoping to get some ideas about a recurring problem with a 2015 VRS so I can discuss with mechanics. For the last couple of months the car has been cutting out. It originally happened now and then when idling. I wondered if it was the start stop being a bit eager, but turns out not.

We don't tend to idle for long before pulling off so it didn't happen much until one day about a month ago the car cut out while driving. Given the concerns I took it straight to our local mechanic who got lots of BCM faults showing and a low 50CCA reading from the battery so he replaced it. It drove OK for a few days until cutting out when idling started again. This time I took it to our Skoda dealership who found also unrelated oils sump and coolant leaks and did a service. They claimed some kind of pin or such like was loose and they removed and cleaned it or something and that was the fix for the cutting out. I found this was not described on the invoice so can't give the details yet.

The car drove beautifully the next day, but the day after it cut out several times at lights and once in motion for my wife on the way to work. Luckily her route passes the local mechanic so we left it there again. I went down and the mechanic saw the cutting out while idling for the first time. The pattern is idling can be smooth for a bit and then can get rough, or can start rough. Either way it can then be fine or go juddery (very rough) before cutting out. There seem to be levels of rough and it can go rough to smooth and back. Hearing it he instantly thought it was more likely mechanical than electrical. He put some fuel system cleaner in and it made no difference. The final step was he kept the car while waiting for his parts place to open after Xmas and saw the same problems every day when moving it and kept getting a reading for a camshaft sensor fault so replaced that. Of course it drove like a dream during his test drive. When I picked it up yesterday I felt a bit of roughness in the idling, but it behaved and got smoother. Until my wife drove it this morning and it cut out 3 times in motion within 1km. When I drove it home it was happening every 100 metres or so. But it did get better after a km or so, and so I added a trip round the block and it didn't cut out!

I'm now $1,500 into this with the local mechanic and $4,200 with the Skoda dealership - though only $160 of that was for supposedly fixing the cutting out, what it went in for!

Any ideas on the mechanical or electrical side? Before getting the camshaft sensor code repeatedly, the local guy said it could be a rusty fuel tank, rare but fits the pattern in his view. I do wonder if the random periods when it runs well or badly combined with it getting worse over time could fit the idea of rust moving in the fuel unevenly. There's not been a single moment where the car failed to start btw.

Don't really know what to do now. Once more the car is undrivable on a Saturday or public holiday when I can't just ring Skoda. Clearly this is a dangerous car that needs fixing and somebody, probably Skoda needs to get to the bottom of it, but I don't have any experience with this kind of situation. I can wear the cost so far. From now I think the manufacturer should take some responsibility to solve the problem. So any thoughts about how I go about that also appreciated before I pick up the phone.

[h100vw]

Its been a couple of decades since petrol tanks were steel. Even MK2 Golfs in the 1980s had plastic ones.

I cant help with the diagnosis, not being there personally but I would be running with a logging device going. I'd watch the fuel pressure, both from the tank and the HPFP.

Crank angle sensors can cause dramas and not throw codes.

I just fixed up a MK6 GTI that had a problem with hot starting. The cam chain tensioner broke, I fitted a replacement motor that drove great but wouldnt start without a lot of cranking once it had reach temp.

Monitored fuel pressures, which seemed like the most likely cause. Either the pump or the controller. Neither actually seemed to be the problem after watching the fuel pressure to the HPFP and live data of the high pressure fuel.

The ECU kept on coming up with a cam sensor implausible position fault.

Eventually, I stripped out the cam bridge and found that there was massive scoring inside it. The end of the cam was also worn badly. Like a spun bearing. The filter in the bridge was missing, so that had probably been pushed through into the cam adjuster. Once up to temp that oil was unable to keep pressure in the adjuster during cranking, the inlet cam timing went out and the engine would struggle to start.

So most of a day later, having replaced the timing chain and cam shafts the car now starts well, regardless of temp.

So maybe the position code is a red herring or a symptom of a different failure. Maybe a cam magnet or 2?

[Guyzer]

Thanks for the info. I'll raise some of those issues and see what they say.