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Hi I have owned my golf since last October. About a month of owning it, it started to do the annoying long cranking before it finally starts. I have vcds and the only fault code it came up with was ignition switch intermittent fault so I replaced that yesterday still having the same issues. I have also had the following either replaced or tested.

new battery
Fuel filter x 3
Oil has been dropped and filter changed
Injector seals replaced
Intank fuel pump replaced
Oil pressure sensor replaced
Turbo replaced
Thermostat replaced
Earth’s checked
Camshaft/lifters ect replaced
Waterpump ect replaced
Clutch & dmf replaced
Egr valve replaced
Alternator checked
Air filter replaced
I am literally ready to set fire to the sodding thing, any help or suggestions as to what/where to check now would be appreciated.
 

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probably an air-leak in the fuel system... fuel returns back to the tank somehow... this could be a leak on the seals of the tandem pump, perished fuel lines, or a leak on the fuel filter seals or the housing... (could also be on the injectors by the way but you clearly stated you've got new seals on them)

to test this out, leave the car facing down hill overnight ( back higher than the front) if it starts up way quicker than it did before, than it's an air leak that let's fuel return to the tank.
 

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if you've done that it leaves the fuel lines ... a dirty way around it is to plumb in a non return valve into the fuel return pipe... if that stops the hard starting, well than it would be better to replace the fuel lines.

Another thing that can cause hard starting when cold is when the timing is off... and yes the car will eventually start, and run properly... but you'll notice more engine movement when trying to start.

can't think of anything else you haven't addressed yet..
 

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well if that is the case than it should fire up quickly ( 0.5 is in spec) leaves you to get a non-return valve and put it on the fuel return line, best to put it between engine and fuel filter.

ps check the leak off pipes too as they are known to be the cause of the air seeping into the fuel system... afaik you can buy new ones from almost anywhere by the meter and you just cut it to size and replace as needed. (last time i bought that for a diesel car it costed 5 pounds per meter and i had loads left)
 

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well than it must be timing related... only one thing left for you to do now, re-check the timing, and if that is spot on, check the fuel filter housing as that is another point that can let air into the fuel system.... it might have a little crack or doesn't seal properly.

Note on fuel filter housing check it first thing it should be filled to the brim, so clamp off the fuel pipes going into he housing and coming off the housing before opening it to check it. That way you stop the fuel escaping that is already in there, so you can see if it actually is filled.

if that all checks out there are 4 more things:
  • the intank fuelpump doesn't prime well (unlikely as you've replaced it, so i figure the only thing wrong with it would be a clogged mesh filter on the pump itself, pull it up to check the filter in the bottom)
  • check the state of your battery before starting (it has to be well above 12.5v closer to 13.1v, i know you replaced the battery so if it is low, you probably got a bad alternator )
  • check the startermotor as it could have excessive ware on the shaft causing it to not operate at the right RPM to start the car ( eventually it will stop working, tell tale is when turning the key sometimes it clicks before actually turning the engine over)
  • the glowplug relay could be done for if it has never been changed but that will trigger a faulltcode so if you haven't got one it is fine.

I can't think of anything else that can cause the cold start issue you are experiencing as you've gone through almost every single possible solution, including adding the non return valve in the fuel lines before the filter housing.
 
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