On Tue, 24 Aug 1993, Scott 'Dr. Pain' Turner wrote:
> I haven't been using my B much for the past six months or so and
> as luck would have it, it came up for a smog check (CA). This is
> a 1979 MGB with the usual plethora of smog gear.
>
> Anyway, I took it in for testing (which my work offers for a very
> cheap price) and it came back high on HC and CO at idle. The actual
> readings were HC (ppm) 243 [permitted 150], CO (%) 3.14 [permitted
> 1.2]. The mechanic also said the EGR valve was working but apparently
> blocked. (Of course, he also said the catalytic converter was missing
> - he just didn't know where to find it.) Timing was fine at 10 btdc.
>
> Anyway, my question is, what do these readings mean? The mechanic
> said they were likely because the fuel mixture was too rich.
> Presumably I can fix this with my colortune and the adjustment tool
> (if I can find it). I can also pop off the EGR valve and clean out
> underneath it, which should fix the blockage problem. I guess I
> should also put in new plugs while I'm at it. Is there anything else
> I should do? (Well, I should get new carpets, a new top, and pay more
> attention to my wife. But you know what I mean.)
>
> -- Scott T.
HC means unburned hydrocarbons- fuel that didn't get burned all the
way. Complete combustion will give you CO2, water and air in the exhaust,
plus NOx if the temperature was high enough, but the nitrogen doesn't
really participate in the combustion process all that much. So if you have
high HC and CO instead of CO2, that means that there wasn't enough oxygen
to complete the combustion. You will need to check the things that
could be restricting your air flow, or increasing your fuel flow, like
air filters, or the choke operation.
-Jean H
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