B6 Passat Starts then cuts out immediately when cold ....

[Renars]

Its not going to cut out like that because of air/boost problems.
You can see pressure in fuel system made by in tank lift pump, its regulated by valve and monitored.
Its sudden lack of fuel, because ECU thinks it has to be cut or it just cant see it happening.

Hmm also there is valve in fuel return lines that keeps fuel pressure at 14.5 psi, 1 bar.
If that is failing maybe injectors fail to work without back pressure from fuel return.

Fuel Return Line PressureLimiting Valve – Keeps thepressure in the fuel return lineat 14.5 psi (100 kPa / 1 bar).
This maintains a forceequilibrium at the pump/injector solenoid valve needle

[D-Man7]

Ok thanks very much for that Renar and Phillipharmes, it’s much appreciated! I’ll do some investigating this weekend!


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[DMitch16]

Ok thanks very much for that Renar and Phillipharmes, it’s much appreciated! I’ll do some investigating this weekend!


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If not done already - check fuel pump relay and associated fuses for correct seating and contact. Sometimes meter testing gives a good reading for the fuse itself but if the contact of the blades is bad then you can get intermittent voltage issues that don't always fault out.

[D-Man7]

Ok thanks for that, is the fuel pump relay under the dash on these b6’s ?


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[DMitch16]

So.........


I've just fitted a glow plug to the car (just one at the moment). It's 3.5 degrees Celsius outside which would normally cause the car quite a lot of bother to start. It fired up and I thought all was good as normally it dies instantly on first start up, but it ran for about 10 seconds then died. I kept starting it and it would run for about 10 - 20 seconds slowly increasing to 30 seconds before dying only throwing the occasional 'limp mode' where it will hardly rev.


I was watching it on vag com and the engine speed sits at about 903rpm for so long then it drops down to 820rpm after a while which sounds slightly low


I'll have to try it again in the morning to see if it's a consistent slight improvement or just a fluke!

My 170 idles at 800 on the button in summer, 900 when cold like it is now, and once up to full temperature sits at a constant 750 rpm give or take for either climate. Your idle rpms are therefore pretty normal.