Inlet valve carbon build-up

[nicrobell]

Apparently, direct fuel injected petrol engines can acquire a build up of carbon deposits on the back of the inlet valves. This is caused by crankcase vapours being fed into the inlet system. These oily vapours can adhere to the hot valve and form deposits over time. Older engine designs introduce petrol upstream and therefore tend to wash the inlet valves during the induction stroke thus reducing carbon build-up. I would be interested to find out if anyone has opened a direct injected engine and what deposits were seen. I wonder if Ford have addressed this problem and can offer any advice to reduce the carbon build-up.

[Peter B - CV8]

Yes, most manufacturers have taken steps to reduce this well known problem. It involves getting their service advisors to give you a call recommending a "top end clean" when you have the car in for a service..
Some makes suffer this problem more than others. From memory VW 7 Audi are pretty bad.

[rondeo]

Mine's getting the same fuel economy as it was 5 years ago,
diesel but.

Is there a difference, petrol vs diesel?

Any link to info?

What does a 'top end clean' involve'?

Shouldn't the oily vapours adhere more to a cold valve (inlet) than a hot one?

etc etc

[rondeo]

I can see it now, hot valve would turn the oil vapour to carbon.