TPI Questions

[James Boughton]

I have to admit that I am not very familiar with distributor advance
systems.  I was attempting to put a mechanical and vacuum advance
distributor on my Camaro, but never had the time and finally sold
the car.  This was my experience with distributors.  So that said, I
would guess that since on non-ecu cars the EGR is controlled by
vacuum that you would have to modify the vacuum advance function
of the distributor.  Let me see if I can get a little advice on how much
to modify the spark timing and I will get back to you.  Overall, it sounds
like you went the right direction - less advance for the same vacuum 
levels.

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From: 	Tom Cloud[SMTP:cloud at peaches.ph.utexas.edu]
Sent: 	Wednesday, August 13, 1997 3:51 PM
To: 	diy_efi at coulomb.eng.ohio-state.edu
Subject: 	RE: TPI Questions

James Boughton wrote:

>EGR is used to decrease NOx emissions, as well as to dilute the
>incoming mixture to improve fuel economy.  Because EGR causes
>the burn rate of the mixture to decrease the spark advance must be
>increased.  So for an engine calibrated with EGR there is a spark
>advance increase any time the engine controller thinks the engine
>is breathing in EGR.  The problem with removing the EGR valve
>is that some people don't let the engine controller know that EGR is
>not functional (to keep the check engine light from coming on).  This
>means that the engine controller thinks you have EGR when you really
>don't and therefore the spark advance is far more than what it should
>be.  This can cause very high peak pressures and possibly knock.
>I know when I did this I holed a piston:-P  I wish somebody had told me
>what I am telling you.

so, James, on a non-ecu engine (distributor with
centrifugal & vac advance controlling timing) how would
you recommend compensating for the "loss" of the EGR
function ?    I had my distributor "re-curved" (actually
think he just set the vac advance spring a little stiffer
 -- talking Ford vac advance canister)

Tom Cloud