On 15/10/2017 12:58 AM, Scott Dorsey wrote:
> Bill Vanek > wrote:
>> Finally, this is the tough one. There is an issue called "coking" on
>> some vehicles. Carbon builds up in the intake near the ports, and/or
>> on the intake valves. That carbon - the coking - absorbs fuel vapor
>> when you are trying to start the engine, and the result is that the
>> engine is too lean to start easily. The main characteristic is that it
>> is much, much worse when cold. The fix is obvious if it is a buildup
>> on the valves, but if it's in the intake, that's another issue. Good
>> luck with that. And I don't know of a proper diagnosis for this. It's
>> more like a process of elimination, and that's all that's left.
>
> Is coking really an issue with modern engines and fuels?

Yes but it has a lot to do with how the fuel enters the engine. In a
diesel, the fuel is injected directly into the combustion chamber. Same
as with Gasoline Direct Injection. That means that any fuel, or oil,
that gets into the intake system on these engines can *burn* onto the
*back of the inlet valve* and turn into a hard carbon build up - coking.
If you're wondering how fuel gets into the manifold if it's injected
directly into the combustion chamber, think of PCV and EGR systems.
Also, some GDI systems use valve timing as a pseudo EGR system.

This should explain it;

http://www.aa1car.com/library/intake...di_engines.htm

and this;

http://www.aa1car.com/library/what_i..._injection.htm

>
> I remember my father talked about taking the car to the mechanic every
> spring to pull the heads and scrape everything down with a chisel,
> back when HE was a kid.

Different kind of coking. That's combustion chamber coking.
>
> Shouldn't be TOO hard to clean the intake.... but the original poster
> has had the carb off and should have seen if it was gunked up in there.
> --scott
>


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