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I have a Ford Focus MKII (British market) with the 1.8 Duratec Engine that is very hesitant starting when warm.

The starter cranks powerfully but the car will only come to life when pumping the accelerator, sometimes it'll start but at very low revs (until I pump the accelerator).

In about 20% of warm engine scenarios it doesn't need this treatment but it never occurs when the engine is cold.

Through research I've heard about something called 'vapor lock' which appears to describe this - the remedy (drop the accelerator at the same time of killing the engine) seems to resolve the issue for the next startup.

Do I have vapor lock? Any pointers of how to prevent this properly?

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    Vapor lock is almost exclusively associated with carbureted engines. Not sure what is causing your issue, but I doubt it's vapor lock.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Feb 26, 2016 at 11:12
  • Thanks for clearing that up, I'd read something like that also but the symptoms and solution seemed too coincidental
    – m.edmondson
    Commented Feb 26, 2016 at 11:39
  • Does the temperature gauge show proper temperature? Did you check the fuel pressure regulator?
    – I have no idea what I'm doing
    Commented Feb 26, 2016 at 12:33
  • Yes the temperature gauge rises with the temperature of the engine and stays reasonably stable. No I haven't checked that - I'll check my Haynes to see how to check it
    – m.edmondson
    Commented Feb 26, 2016 at 12:37
  • It's not common on Fords but sometimes if the purge valve is stuck open it can cause hard starts.
    – Ben
    Commented Feb 26, 2016 at 20:58

1 Answer 1

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In fuel-injected systems, hot-start problems indicate that the fuel line is unable to maintain pressure.

This could be due to a few things related to the fuel supply line, including:

  • a leaky fuel injector
  • minute cracks in the fuel line which leak fuel when under pressure
  • a bad non-return valve in the fuel line which is allowing pressurized fuel to flow backwards

The reason why this happens only for hot starts is because the fuel is more likely to vaporize as temperature increases. In order to avoid vaporization problems the fuel lines are expected to be pressurized during a hot start.

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  • Thanks - I'll run through each in order to try and diagnose. Any ideas why dropping the accelerator (on start up or shut down) seems to help?
    – m.edmondson
    Commented Feb 26, 2016 at 14:05

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