smog numbers

my 89 civic just passed smog, but only just - the NO emissions are very
high. question from the smog gurus:
anything i can do for the old girl, other than replace the catalyst?
/is/ it a catalyst problem?

15mph
CO2 = 14.7%
O2 = 0.6%
HC = 31ppm
CO = 0.09%
NO = 853ppm

25mph
CO2 = 14.6%
O2 = 0.5%
HC = 20ppm
CO = 0.08%
NO = 788ppm

max NO #'s are 859 and 798 respectively.

other than that, everything is all factory and adjusted per the honda
manual.

 

jim, don't panic.

What are the car's numbers from previous years?

I have personally found on /numerous/ occasions with different cars that
I/M testing equipment has a tendency to give weirdly skewed results on
particular occasions that do not repeat on subsequent testing.

If this is out of character for the car, chances are excellent that it's a
one-time glitch. If you retest, I'll bet you'll find the numbers go back to
what you're used to seeing, with no work having been done at all.

Your other numbers are sparkling for an '89. Must be all that maintenance,
eh?

 

the previous smog numbers were similar, only just squeaked by on NO, so
there's consistency. maybe i should swap in a crappy old set of spark
plugs and retard my ignition a touch before my next test - weak
combustion would fix the "problem".

 

Don't they check your timing during CA smog checks?

I've been told that every extra one degree in timing advance is worth
about 100ppm in NO. If that's true, you could retard it to 14deg BTDC
(or your allowable minimum) and you'd be OK for that.

Another thing you can try is to make sure the fuel system is full of
Sunoco 94 or other heavily-oxygenated fuel. And if it's possible, get
tested on a wet, rainy day (yeah, I know this is SoCA...). Ambient
moisture may help drive combustion temps down.

Have you checked for air leaks into the exhaust before the cat? These
will really drive up NO readings.

If all the above is tried to no avail, then you probably do need a new
cat, as the reduction side has had the biscuit.

 

noted. it's dead on right now.

all good.

that's what i suspect. but i'll plod along until the next time it needs
a test.

counterintuitive to all this though is that this engine takes a really
long time to warm up. new[ish] radiator, new temp sensor, two new
thermostats, all new hoses. if the NO levels are high, it implies it's
running hot, but the opposite is the case. all very weird.

 

Have you inspected your EGR for proper flow? These old cars won't set error
codes for insufficient flow.

It's my understanding that high NO is unrelated to cooling system
temperature; it is solely a function of peak combustion temperatures. It is
therefore possible for a car that appears to run cool to have excessive NO.