My '06 Focus 1.6 TDCi Sport has been having starting problems recently. The engine will turn over, but doesn't fire up for about 3-4 seconds. It's worse from cold start.

The glow plugs were changed last year, and have been checked as ok this week.

I would replace the battery, but not sure that is going to fix the problem, as the engine is turning over. Idling voltage measured at 13.92V across the battery terminals. Is this about right? I am reluctant to burn £100 on a new battery, to find it doesn't fix the problem.

Alternator was replaced about 2 years ago.

Took it into local dealer (not Ford) who said there was nothing wrong with it. However I disagree, as I've driven it for 5 years, and the car has been starting perfectly until very recently. Something is not right, but I don't know what it is. I'm also worried it's going to fail to start at some point because this has been getting gradually worse.

There are no fault diagnostic codes.

It's done about 88k miles.

Any ideas on probable causes for this, or anything I can check before I resort to Ford dealer?

Just another thing to add - I think I used to hear a humming as I turned the key (fuel pump starting up?), and I hear nothing now. Could the fuel pump have broken? Also, where is the fuel pump, because I believe that the fuel tank doesn't have an integrated pump. Is that right?

When u say 3 to 4 seconds does nothing happen then just starts cranking over or is the engine turning over an only starts after 4 seconds

It's turning over for those 3 seconds before it finally starts.

There no pump in the tank have u changed fuel filter recently did u have battery tested at ford dealership wit specialised battery tester

3 secs to start doesnt sound like a problem to me ive yet to find a car that starts bang within a milisecond all cars turn over for a second or more

There no pump in the tank have u changed fuel filter recently did u have battery tested at ford dealership wit specialised battery tester

Fuel filter was changed last July. Battery hasn't been tested. I was going to take it down to Kwik Fit for a free battery test. I also measured the voltage myself, it seemed a little under what it should be. Having said that, the battery is happily turning over the engine so I have my doubts that it's a weak battery.

3 secs to start doesnt sound like a problem to me ive yet to find a car that starts bang within a milisecond all cars turn over for a second or more

True, but I've driven this car since 2008 and it's always been a good starter, within a very short time after turning the key. But recently it has been struggling more, and sometimes when it's really cold, I've had to crank it for over 5 seconds.

I defo get battery tested at least u can rule it out

its a diesel im assuming in the cold youre turning the key and waiting for the glow plug light to go out first before starting diesels will struggle in the cold hence why glow plugs are needed in the first place they have to get very hot to ignite the diesel ive driven lots and lots of cars when i worked for a garage and it sounds like youre worrying over nothing get a free battery test done but if you spend money im so confident its fine ill tell you to whack it in an envelope and send it to me if youre eager to waste it

its a diesel im assuming in the cold youre turning the key and waiting for the glow plug light to go out first before starting diesels will struggle in the cold hence why glow plugs are needed in the first place they have to get very hot to ignite the diesel ive driven lots and lots of cars when i worked for a garage and it sounds like youre worrying over nothing get a free battery test done but if you spend money im so confident its fine ill tell you to whack it in an envelope and send it to me if youre eager to waste it

I think you're right. Usually it would be in the garage overnight, but we have builders in so it's been on the driveway overnight. Thanks for the starting tip I wasn't aware of the need to heat up the glow plugs properly. I'll pay more attention to the dashboard icons.