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The car is a Renault Modus 1.4 16v Dynamique 5dr 2005. The symptoms are:
Car wouldn't start last week.
The car cranks but does not start.
Push started the car in 2nd, engine starts.
Took The car for a drive, stopped the engine, started it. All fine.
Came back next day, car cranks but does not start again.
Battery should be fine. Replaced it 2 weeks ago.
If I push start the car again now, drive round the block, the car will start normally again.
Any help would be much appreciated.
It could also be the Crank Position Sensor. It is mounted on the flywheel cover and if it gets contaminated with dust from the clutch it can stop the engine from starting. It confuses the average guy as it looks like either a fuel or ignition problem. It is held in position with two bolts. Might be awkward to get to. Hope this helps.
While your question is pretty thorough, I'm assuming a few things in this answer that you didn't clarify;
When you crank the engine, and it doesn't start, I'm assuming it's a smooth crank without hiccups. By that I mean it isn't trying to start, it just cranks.
You have the petrol model, not a diesel.
It uses an electronic push-button start mechanism.
From what you describe, it sounds like either an ignition fault, or a fuel-supply issue. Since the car runs when push-started, and since modern vehicles are fitted with electronic timing systems, it's unlikely to be that, so most probably a fuel-supply issue. Maybe the pre-start fuel pump is on the blink?
A Test You Could Try
Some Renault's have a manual primer pump that looks like a black rubber bladder under the bonnet. Your user manual will give more details - it's usually used in the event that you run out of fuel.
Try pumping it a few times before you start the vehicle and see if that helps - if it does then you probably need a new fuel pump. Best to confirm with a garage. If you don't have that device, you can't test it unfortunately.
Other Considerations
If you park on a steep gradient and there isn't tons of fuel in the tank, it might not be picking up any, but that's very unlikely in modern vehicles (used to be a problem in older Kia's).
If the spark plugs are clogged or there's loads of water around the ignition system, it might be difficult to start when cold. However, if it's regularly serviced there's no reason to suspect either.
That's all I can think of right now. I hope you figure out what's up!
If the car drives for about half an hour and switches off or parked off and within 10mins or so of trying to restart the vehicle, suspect the crank sensor. The reason is that the crank sensor is impaired by dust or dirt.
Remove, clean and replace. It controls timing (spark) so if the tank is full and you hear the engine fuel pump buzzing sound in the engine compartment it means that it is supplying fuel. Suspect the pencil coils too.
