OK, so my car has had a stutter of nearly a year and nothing has fixed it. I thought i had fixed it by replacing one of the VCT solenoids, but it was short lived.

However I have now seen a pattern to the stutter. If the tank is low on fuel its worse, after a fill up it almost goes away. However I don't believe its related to the pump, since it was replaced within the last 12 months and that had no effect.  The fuel cap is sealing and lets air in as the fuel does down, so its not due to a vacuum in the tank, so maybe its due to excess pressure. There are no error codes from the EVAP system, so im still not sure what's going on.

 

Ive now started releasing the pressure daily to see if the car remains OK as the fuel drops. If it does then any ideas what could be wrong? I was under the impression that if the EVAP system was blocked it would throw a code, but maybe not if its blocked before the carbon canister or in the canister itself.

I had a mk4 Escort which kept having problems with cutting out and stuttering , not all the time but on occasional days. I spent many many hours over many weeks on taking carb apart, checking for dirt inside fuel tank etc etc. Eventually cured it by drilling a very small hole in the fuel cap. It clearly was a problem with vacuum in tank as it used the fuel but it took me a very long time to work this out as it was intermittent.

I know by modern standards having a vent hole in cap sounds very bad but all cars were like that years ago (perhaps up to 1980ish?)

My problem seems to be the reverse, the problem is tank pressure should be monitored, and a hole in the cap would cause an error code (even a small hole). I will test it though by running with the cap loose for a short while.

On this issue/topic. I've got my fresh car today,09 focus Zetec s 1.8.  I have no filler cup,only the flap,is this right ? 

Yes, cap less fuelling. That's how they come.

36 minutes ago, vavavoom said:

Yes, cap less fuelling. That's how they come.

Cheers mate,seemed very strange not having to unscrew the cap lol