EGR Corrections

Terry thartman at gte.net
Sun Jul 26 17:42:15 GMT 1998


Bruce Plecan wrote:

> Does the Diacom show the burst knock activity?.  
>

I'm not sure what your term busrt knock activity is referring to.

>  Does it show the EGR timing addition?.

No - not this just by itself.

> Becomes a matter of what they call requested timing.

What Diacom displays for my ECM is Spark Advance Relative to TDC
which is the total spark advance applied to the engine's ignition
system by the ECM.  The spark advance value is relative to Top Dead
Center and is is displayed in degrees.

It also shows Spark Advance Relative to Reference which is the amount
of spark advance that is being applied to the HEI module by the ECM. 
The spark advance valve is relative to the reference pulses received
from the distibutor and my be added to the base timing to obtain the
total advance.

Diacom shows the Spark Control Counts which is just a counter from 0-255
that will just roll over to zero after the upper limit is reached.

As far as EGR info, Diacom displays EGR Duty Cycle which is a the 
percentage of the EGR solenoid ON time vs OFF time.   On my
car, the EGR valve is controlled by the EGR Solenoid which in
turn is controlled by the ECM.  When the EGR Solenoid is de-energized
it allows engine vacuum pressure to operate the EGR valve.
 
 
> > This would indeed be a bad thing as that
> >would also imply that the data from the ECM diagnostics would be
> inaccurate....
> 
> How would you figure that???

By the way you presented your original statement.  My question was really
whether the Diacom would show the total timing - and I think
that it does.  

>  Diagnostics is for fault finding, 

I disagree.  I find that Diacoms' diagnostics are a good tool for
tuning...

> if it's intended to operate a certain way, then there is no error.

This is true!  But "indended operation" is what I think we
are trying to discover here.

T.



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