My knowledge of carbon deposit build-up and its symptoms are
more at the general level so that if these symptoms occur, it's
an area that I know I should check. I'll speak to someone
who has detailed knowledge and put up a post.
In general, carbon deposit is one of the residues resulting from
the combustion of gasoline. The efficiency of the ignition system
determines how much, if any, build-up occurs. A rich fuel mixture
also results in carbon deposits because the combustion is not complete.
Places which you can see if this occurs are the spark plugs,
inside of the exhaust tip and the throttle body. An extreme example
of this is seen when the vehicle has become flooded and black smoke (black
soot)
comes out of the exhaust.
If the build up is bad enough in the combustion chamber, it can
result in 'run-on' (motor runs after key is turned off). In this case,
the carbon deposits are so plentiful and so hot enough as to cause
combustion of the
gas/oxygen mixture even though the ignition has been turned off.
Those who have/had muscle cars with carburetors will be familiar with
the above. On Dodge vehicles which had the EGR system, there was a
passage running from one side of the motor, under the carburetor, to
the other side which took the unburnt mixture from the exhaust back to
the intake. It was notorious for plugging up with deposits and you had to
remove the intake manifold to clean the passage up.
On today's vehicles, with electronic ignition system, fuel injection and pcm,
these extreme symptoms are less likely to occur and build up is more
gradual.
Pinging occurs when there is enough build up and the hot deposits
cause combustion at the wrong time.
I've found that cleaning the throttle body remedies the situation, assuming
that the injectors have not become plugged or the spark plugs have become
fouled.
I think the above is correct. Hope it helps.
Bob
This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 12:11:28 EDT