On Fri, 27 May 2005, Mr. Minnow wrote:

> I took my car(87 5th Ave with a 318(5.2L) v8) in for an emission test and it
> failed miserably
>
> Here are the results:

It's *very* hard to read your results -- the tabulation didn't come out as
you tried to make it do -- but it looks to me as if your results a

HC: 197ppm (limit 83ppm, FAIL)
CO: 0.16% (limit 0.46%, PASS)
NOx: 1220ppm (limit 893ppm, FAIL)

Your CO is about 1/3 of the allowable limit, and is an excellent reading
for a carbureted car -- but your HCs are more than double the allowed
limit, and your NOx is 1/3 higher than allowed. This combination of
results suggests your engine is running so lean that it is misfiring.
Those cylinders that do fire produce a great deal of NOx due to the lean
mixture, while those that do not fire produce a great deal of HC due to
noncombustion.

(These '85-'89 civilian M-body cars with the Holley 2bbl don't generally
run very well in stock form, even when everything is set by the book. Lean
surge under steady throttle is the rule, rather than the exception. Not
that this helps you -- just saying.)

So, what's causing your misfiring? Could be any number of things. A faulty
Oxygen sensor in the driver side exhaust manifold (how long since you
replaced it?). A faulty carburetor, a faulty Lean Burn computer, a plugged
fuel filter...it might not even be a lean misfire at all; your readings
could also be caused by the reduction portion of the exhaust catalyst
system having reached the end of its life, resulting in very high NOx
tailpipe readings and insufficient free Oxygen in the exhaust stream to
allow the oxidation section of the catalyst to clean up the HC.

Time for some systematic diagnosis by someone who has considerable
experience with the carbureted Mopars of the mid '70s through late '80s.
Just throwing parts at it will get very expensive long before the problem
is solved.

DS