TPI Questions

[James Boughton]

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.

Since EGR is only operational under part throttle conditions it is really
arguable that it should be used even on streetable performance
applications.  I will say that I wouldn't put it on my car, but if faced
with using an engine controller that expected it to be there I wouldn't
hesitate to install it.

Jim Boughton
boughton at bignet.net

----------
From: 	Jeffrey R Muehl[SMTP:JRMUEHL at mail.delcoelect.com]
Sent: 	Tuesday, August 12, 1997 10:03 AM
To: 	diy_efi at coulomb.eng.ohio-state.edu
Subject: 	Re: TPI Questions





I was hoping someone would jump in here.

Do you have any evidence of the engine knocking without EGR?

I have the same question - do I want it or not?  I'm also not concern with
economy, only power.





>I'm lost, for a performance engine, do you want egr or not ?  When I built
my tpi 350, I pulled the egr valve and stuck >a blanking plate over the
hole instead, oh, I also put the little metal plates in the manifold
gaskets where the egr is >meant to breathe through.  Was this a mistake (I
don't care about economy, only power)?>>
>
>
>Dan     dzorde at geocities.com
>
>
>The EGR valve is still present and connected, but doesn't actually do
>anything since there isn't a supply of exhaust gas to the valve.
>
>Grounding the EGR feedback wire will set off the SES light (it simulates
>the EGR being stuck in the open position)
>
>Leaving it disconnected will also occasionally set off the SES light
(there >are a few cases where the ECM will command the EGR to actuate, then
look to >see what happened.)  Fortunately, temps down here are high enough
that this >doesn't happen often.  (been about 4 months since the last time
the code >went off) It will also clear itself within a few minutes of
driving.
>
>Someday I'll have an EGR flange welded to one of the exhaust headers to
>supply external EGR.. but it's a low priority.