EGR Corrections

[John Hess]

Unfortunately, your spark advance relative to TDC is calculated against
what the VIN number translates as initial advance plus the programmed
advance.  It is only accurate if the engine is properly timed according to
the manufacturer's recommendations.  For example, Crane Cams indicates that
my initial advance should be 10 degrees (not the stock 6).  This means that
if I simply set the initial advance up 4 degrees at the distributor, Diacom
will be off by 4 degrees at all readings.

At 12:43 PM 7/26/98 -0500, you wrote:
>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.
>
>