Originally Posted by
Robo959
Dear all
I did a 135 mile each way trip yesterday and my trusty “T” reg Focus began to cough and splutter during the last 3o “ish” miles. The tank was full except for around 70 miles of fuel. It was still running, but very strangely as the engine would not rev. I couldn’t pull away quickly in traffic, I had to roll gently and quickly change to a higher gear, then next gear etc. and eventually I’d get to 60/70mph and cruise with no problems …. Until …conditions made me loose speed again or I tried to accelerate and then I could feel the engine missing. 
Here’s the strange bit – I stopped in a lay-by jumped out and played a hunch, I unlocked the fuel cap and released either pressure [more likely a vacuum] which the tank appears to get, usually issues only occur over the last gallon or so when it coughs around when heavy cornering and wants filling before the low fuel indicator comes on. Once the fuel cap is released it seems to be OK for the remaining fuel in the tank. Anyway, yesterday once I had released the cap the engine would rev to 7k without a problem and pull away just as if nothing had happened.
To my reckoning there were only two things which might have been brought into play – 1) the fuel cap - pressure/vacuum issue and 2) to do this I had to switch the engine off to unlock the fuel filler flap, did this reset the ECU or have other effect?
The issue was repeated on the journey home at around the same mileage +/- although not quite as badly – there was a difference in ambient temperature and on the return route not the stop start in very heavy traffic on an Easter Monday. About 30mins after arriving home I did another short journey of 10+miles in each direction and the engine never missed a beat.
I’d very much appreciate any pointers you may have on where to start looking to solve this one, please.
TIA
RobO
hi i got the same prob tried fuel cap for pressure worked for a bit,new filter no difference, not sure if its tps,crank,temp,cam sensor if you cure yours let me know and vice versa from stuart