EGO and the Smog Pump

[Steve Meade]

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> From: Johnny <johnny at johnny-enterprises.com>
> To: diy_efi at coulomb.eng.ohio-state.edu
> Subject: Re: EGO and the Smog Pump
> Date: Sunday, July 13, 1997 12:55 AM
> 
> Robert Harris wrote:
> > 
> > Dah, correct me if I am wrong ( aw go ahead and do it anyway)
> > but doesn't the EGO sense total oxygen in the exhaust stream
> > and get "happy" around stoic?   If true, then when we shove
> > extra oxygen via the smog pump into the exhaust, do we not have
> > to shove unburned fuel from a too too rich mixture into the exhaust
> > to make shore that the result is stoic at the sensor?  Am I missing
> > something here or is the total extra oxygen so low that it doesn't
> > make much difference in the fuel consumed??
> 
> There are a couple factors involving the smog pump. Firstly, by
> injecting air (has O2 in it) into the exhaust manifold right at the
> port, it enables any unburnt hydrocarbons to get burned, or reburned
> even. Besides cleaning up the exhaust, this post combustion also
> increases the temp going into the cat, which helps the reaction that
> takes place there. Secondly, at least in the old days, exhaust sniffers
> measured hydrocarbons in ppm, so if you add air, you are reducing the
> ppm, even though the actual total emissions would stay the same (except
> for the reburning effect). This was especially true in the few years of

	They still do measure in PPM in the US judging by my last smog test. How
much smog is actually reduced by the smog pump action? 

> smog pumps with no cats. Because the O2 part of the injected air gets
> used up in the post combustion process, it shouldn't change the output.
> I'm not even sure if air pumps are still the rage or not though.
> 
	I was looking through my Porsche parts catalog and there are smog pump
listings for 911's up through '94, all 928's (V8), early 924's (2.0L VW
I4), and 914 2.0 (2.0 VW w/Porsche heads). So, apparently smog pumps have
been pretty popular at Porsche until recently. I don't know how adding O2
before the lambda sensor could preserve its output though. Does all of the
O2 injected air get used up in post combustion burn? If it does, than
wouldn't some of the leftover O2 from original (cylinder) combustion get
used too and alter the O2 sensor reading? Or, does it work out that the
reading is preserved since injected O2 won't get used up if there's not
enough fuel which would still read a lean condition?

> Even the cleanest of piston engine combustions are still pretty dirty
> right at the exhaust port. Burning gasoline, even with the best of
> combustion chamber designs, and "perfect" injector and spark management,
> you still have to massage the exhaust to get it to meet the current
> spec. Don't all new US gasoline vehicals have cats? I am no expert on

	I don't know if it's written in legislature anywhere but I don't believe
there are any mass production  passenger vehicles with gasoline internal
combustion engines that don't have cats. Out here in CA you can fail a smog
test "visually" meaning that your car can pass the sniffer test (OK
emissions) and still fail because it has an "unauthorized part or
modification." You may see a lot of parts which say they have "CARB"
exemption numbers. That means their product is registered and allowed by
the California Air Resources Board. Though, I know there are some engines
out there that probably could pass without cats when new. One problem
though is that in the US car manufacturers must warrant the emissions
system for 5 years and lots of miles. If the car ever fails within five
years the manufacturer must fix it. For that reason the cats are a good
insurance policy for clean cars which are clean when new but after 30,000
miles of owner-neglect they might not be. 

	An interesting side note, I bought an '86 Porsche 944 that was originally
purchased in Missourri. It does not have the "California" smog package on
it. I live in CA and had to have the smog done to register my car. Now this
car is 11 years old with 74,000miles and doesn't have the CA smog stuff.
Here's some test highlights at 2500RPM:

	Hydrocarbons:	Allowable: 150PPM  	Tested: 003PPM
	CO%:		Allowable: 1.20%	Tested: 0.01%
	CO2					Tested: 15.4%
	O2					Tested:	0.0%


> what's currently out there in production land. Are there any? Not sure
> about post combustion enhancers (smog pumps). Seems like most of the
> stuff I have worked on had 'em, but I try to stay away from that new
> stuff as much as I can.
> 
> -j-
=-=-=-=-=-=-=-=-=-=-=
Steve Meade
smeade at deltanet.com