Ford focus 1.8 tdci over fueling??

[Wizard69]

Good evening,

I have an issue with my 1.8tdci and was wondering if anyone has had the same issue.

When driving at motorway speeds in 5th gear, if I roll off the throttle taking the engine from load to breaking and roll back on the throttle I get a cloud of white smoke and a back fire, but only above 2000rpm. If I dip the clutch, let the revs drop and then match the revs to re engage the issue doesn't occur. It appears that it happens when going from load to no load then back on load, The car drives fine at all other times, it doesn't burn any oil and fuel economy is normal, there are no fault codes displayed at any time.

[stevieturbo]

White smoke is generally steam/water

Black smoke is excessive fuel..

1. allcoloursmatter

[GreenV8S]

I'd check the coolant level and see whether it's clean, just to rule out HGF.

[Wizard69]

Coolant level is fine, and clean, the smoke is due to overfueling, I'm thinking along the lines of wastegate or sensor failing, if I let the boost drop to zero it doesn't do it, it's only if I reapply the throttle whilst there is still boost.

[Megaflow]

stevieturbo said:

White smoke is generally steam/water

Black smoke is excessive fuel..

1. allcoloursmatter

Black smoke is excess burnt diesel. You can also get white smoke from a diesel that is excess unburnt diesel.

[GreenV8S]

Wizard69 said:

Coolant level is fine, and clean, the smoke is due to overfueling, I'm thinking along the lines of wastegate or sensor failing, if I let the boost drop to zero it doesn't do it, it's only if I reapply the throttle whilst there is still boost.

Seems plausible, but does it explain the backfire? I've seen diesels quite heavily over fuelled without any backfiring. To me, that suggests there is unburnt air coming out together with fuel.