Hot re-start issue

[TheHoof]

Good evening all,

Wondering if anyone can shed any light on an intermittent issue I have.

When restarting my V8 Vantage (4.7) when it's already hot, and it's been left for a while - I've noticed it after leaving it an hour, but it does happen sometimes with a shorter rest - the car will fire up but sometimes it doesn't 'bark' into life, rather it will be a lumpy idle for a second or two before settling in to a normal idle.

I can hear the usual pump priming noise when inserting the key into ignition II. Cranking takes no longer than usual. No check engine lights or error codes.

This doesn't happen when doing a cold start - those are always the full bore loud bark into life and an immediate fast idle. It's not the battery as I've replaced it a month or so ago, and it was happening before the battery replacement as well.

Anyone experienced something similar or have suggestions as to where to start?

[JohnG1]

This is normal.

The bark is to heat the catalysts.

If already hot it's not required.

Nothing to see here.

[TheHoof]

Thanks. Even the 'lumpy' idle for a second or two is normal?

[kabman]

Those symptoms point to vapour in the fuel rail. There is a non-return valve in the pump module that maintains the pressure at circa 55psi when the pump is stopped to prevent fuel boiling. It's a non-return system so the only way out for the vapour is through the injectors. The engine will crank longer than usual and/or run badly for a few seconds until the vapour is cleared..

[TheHoof]

kabman said:

Those symptoms point to vapour in the fuel rail. There is a non-return valve in the pump module that maintains the pressure at circa 55psi when the pump is stopped to prevent fuel boiling. It's a non-return system so the only way out for the vapour is through the injectors. The engine will crank longer than usual and/or run badly for a few seconds until the vapour is cleared..

Thanks for the reply. Yup, that sounds exactly what's happening - rough for a couple of seconds and then all good.

From the parts diagram I can see, the valve isn't available as a separate piece so a new pump is the way forward. Looks an easy enough job from the workshop manual (famous last words)....

[TheHoof]

kabman said:

Those symptoms point to vapour in the fuel rail. There is a non-return valve in the pump module that maintains the pressure at circa 55psi when the pump is stopped to prevent fuel boiling. It's a non-return system so the only way out for the vapour is through the injectors. The engine will crank longer than usual and/or run badly for a few seconds until the vapour is cleared..

The non-return valve you reference, is that in part 24 of the diagram below ('Module Assembly - Jet Pump') or part 22 ('Fuel Pump & Reservoir)? Assume the former...

[kabman]

If the Vantage pump is as I remember, there's a blue plastic part in the main outlet pipe from the pump. This is the pressure relief regulator and one way valve. I can't tell from that diagram if that pipe is available separately.

If you're handy, it can be taken apart and checked. There's probably a tiny bit of debris preventing it from sealing.

This is the valve from a DB9 pump - same principal, just a slightly different layout

.

Edited by kabman on Saturday 11th April 16:11