[s-cars] RE: Emissions Test Failure

[Matthew Russell]

	Hi Gary-

	I have a couple thoughts, but perhaps one of the more technically
experienced people on the list can elaborate...
	<snip>
> The car only failed in HC and only at idle in the basic test. CO and CO2
> w=
> ere a bit high, but within the limits and consistent at idle and 2500rpm.
> I=
> t also failed a more elaborate test on a dyno, in which they plot the
> emiss=
> ions across time and speed. It shows the HC spike off-idle, coincidental
> wi=
> th high CO and CO2 readings.  This leads me to believe it is a richness
> off=
> -idle and not a lean misfire.
	<snip>
> >
> >Great list, Paul. There are, however, a couple of things the originator
> >missed. High HCs are frequently caused by timing advanced too far. I
> >realize that can be called an ignition problem, but it's one introduced
> >by the hand of man and not just a system failure. On cars with
> >adjustable valves, tight valves can also be a major factor in high HC
> >readings, again a problem often induced by the hand of man. HTH, John
> >
> High HC - Hydrocarbons - Indicates a misfire condition (incomplete or
> > > inefficient combustion).
> > >         *  Ignition problems
> > >         *  Carbon deposits in combustion chamber
> > >         *  Overly lean A/F mixture
> > >         *  Increased camshaft overlap
> > >
> End of S-CAR-List Digest
	<snip>

	Have you also checked your Air-flow meter and the connection?
	If I remember correctly, if there is a bad connection or a
mismeasurement on the force of air flowing thru the intake (airbox) this
would fool the computer and create an incorrect air/fuel ratio.
	On my previous cars with Motronic and CIS/KE-Jetronic, the air flow
meter could be checked using a good multimeter.

	The other thought I had would be the coolant temperature sensor
which is also easy to check.

	HTH,
	-Matt
	92 s4