318i slow starting especially when cold

Post Mon Oct 14, 2013 11:44 am

I have had a slow starting problem for a while since I owned the car 2 years ago.
The car has never failed to start but when I crank it over for the first time each day it spins over for around 4-5 seconds before firing. I gather this is fuel related?

After a run if I were to turn it off for 5 mins then restart it again it fires up straightaway. But leave it an hour or so and its slow to start.

Fuel filter has been replaced, feels like lack of fuel pressure but what would cause this?

Thanks

Post Mon Oct 14, 2013 12:55 pm

I'd suspect that after 25 years your injectors are now worn, which causes them to bleed pressure over time. If left long enough, this leak will allow the pressure in the fuel rail to drop, leading to excessive cold cranking times.

Pull the injectors and send them to Injectortune for a rebuild.

Post Mon Oct 14, 2013 2:15 pm

Grrrmachine wrote:I'd suspect that after 25 years your injectors are now worn, which causes them to bleed pressure over time. If left long enough, this leak will allow the pressure in the fuel rail to drop, leading to excessive cold cranking times.

Pull the injectors and send them to Injectortune for a rebuild.

This is all true, and an injector rebuild will likely give you the best BHP/MPG per £ that you ever spend on the car, but the drop in fuel pressure could also be a faulty non return valve in the fuel pump, a faulty fuel pressure regulator, or even a simple leaking fuel hose. (Any fuel smell around the car?)

Post Mon Oct 14, 2013 2:32 pm

Brian, would a perished vacuum hose on the FPR also effect this ?

Post Mon Oct 14, 2013 2:48 pm

jimbom30cab wrote:Brian, would a perished vacuum hose on the FPR also effect this ?

No.

Post Mon Oct 14, 2013 7:31 pm

Thanks for your replies.

I didn't think of the injectors but that would make sense. I shall add it to my list of things to do.

How can I check the non return valve? Is it built into the pump or just outside?

And the same question with the FPR, any simple tests? The car runs perfectly once warm and even just a few seconds after startup. Although for the first couple of seconds once the car fires it runs slightly lumpy until the idle reaches its optimum.

No fuel smells I had fixed a leaky fuel hose under the manifold a few months ago

Post Mon Oct 14, 2013 10:11 pm

Ideally, you need to connect a pressure gauge (~ £10 on ebay) to the fuel feed line to the fuel rail, and see what's going on.
With the gauge in place, you clamp the fuel feed hose to the fuel rail to check the non return valve, and the fuel return hose to check the regulator. If neither cures the pressure drop (assuming we're on the right track) after the engine is switched off, then it's a leaking injector or two.
Non return valve is built into the fuel pump, but BMW can supply an external one to 'repair' a faulty pump.