Popping and banging at the intake manifold

[del mar]

Morning,

Engine is a v6 with two turbos.

At low revs when you come off the throttle quickly it pops and bangs - definitely intake manifold not the exhaust.
Once the car is upto speed runs smooth without issue.

The fuel filter needs changing, and there is a crack in one of the exhaust manifolds. I have new ones but not got round to fitting them yet/

Weak fuel mix / pump ?

Would the manifold allow air to be sucked back in causing problems ?

Thanks

Del

[DVandrews]

Spitting back is usually hopelessly lean fuelling or badly retarded timing.

Dave

[stevieturbo]

Off the throttle ?

Highly unlikely to be the intake manifold...and the fact you mention exhaust leak everything points to that

But as usual more details would be helpful

has it always done this, was some work carried out that lead to it ? etc etc

[del mar]

It has probably done it for a couple of years now - car is a weekend toy so not used that much. As long as the manifold has been cracked ? Really can't remember.

When you start it it would sometimes need a couple of prods of the throttle to get it to clear its throat. When cold it sometimes dies, although starts straight away but when warmed up there are no issues - other than pop/ bangs.


Over the winter I had the intake manifold off for painting, but am reasonably confident there are no air leaks, plus it did it before.

IT does not have mafs it runs a cylinder type modulation valve.

Thanks

[Allan L]

stevieturbo said:

Off the throttle ?

Highly unlikely to be the intake manifold...and the fact you mention exhaust leak everything points to that

Yes a normal engine with a slight leak in the exhaust manifold joints will give a fine exhaust explosion every time you lift off to change up. I had that happen on a rally and the chaps in the next car reckoned they could always see where we had gone by the sheets of flame from the exhaust!
Whether an engine with turbosuperchargers behaves that way I wouldn't know, as the exhaust arrangements are more complex, but I don't see why it wouldn't.

Edited by Allan L on Friday 14th April 18:55