EGR and knock,was DIY_EFI Digest V5 #25

[Robert W. Hughes]

> > The knock is caused by a lack of exhaust flow back to
> > the intake which cools the fresh charge.
> 
> How does the hot exhaust gas cool the fresh charge.... Or have I got this 
> wrong and you mean that the exhaust gas isn't heating the cool intake 
> charge and the cold intake charge is causing the detonation????
Actually, the exhaust gases dilute the mixture and make the combustion
temperatures lower. To compensate for the reduced speed of combustion,
extra timing advance is added by the ecm. If the ecm adds the timing and
the egr is not functioning, (this typically occurs at highway cruise
speeds) you can get continuous pinging which goes away when you step on
the gas.
-- 
Robert W. Hughes (Bob)
BackYard Engineering
29:40.237N, 95:28.726W
Houston, Texas
rwhughe at ev1.net