i had my car inspected 4 times and i tried a number of things to pass. i passed the 4th time. here in texas, you pay for 1 test and if you fail you have a 2nd try for free within 2 weeks. the 2nd time, i failed but the computer crashed, no official printout, and i got a 2nd try for free and i failed again.
here are my emission results for 3 of the 4 tries and what i did to pass.


1 16 dec 2005 (p=pass, f=fail) failed emission

high speed low speed
std reading | std reading
HC ppm p 162 96 | 167 128
CO % p 1.04 .59 | .94 .63
NOx ppm f 1163 1746 | 1273 2161

what i attempted to fix high nox:
1) replaced dist w/ new rebuilt on my shelf & guessed at timing--no timing light
2) checked flametrap --good
3) checked amm term 2 & 6 readings, good
4) checked plastic air ducts to amm & tb, no cracks, holes--good
5) checked dipstick gasket, seems tight enough, but put extra oring on.
6) switched dipstick from my 92 245 to my 86 245
7) checked electrical connections & grounds in engine bay, all good
8) spliced vac from tb to charcoal cannister with supple vac hose.
9) replaced vac check valve from intake man to engine compartment
10) checked valve cover--no oil leaks, no air leaks

2) 25 dec 2005 test failed but no printout so i get a second free try.

how to cut nox again:
1) new spark plugs, dist cap & rotor, air filter
2) checked injectors, readings ok per bentley
3) cleaned amm filament very carefully with carb spray, resistance in range
4) iac cleaned w/ new iac hose to manifold, iac resistance in range
5) o2 sensor heater checked per bentley, good
6) o2 checked, in range per bentley
7) injector resistance, good
8) change ecu w/ spare, no change, both ecu's good (544 & 554)
9) muffler no apparent leaks --checked up & down exhaust
10) change amm resistance from 800 ohms to about 300 ohms
11) did not change oil
12) checked for loose things in cat. nothing loose, no sulphur smell.
13) checked for exhaust manifold leaks
14) checked for intake, injector leaks with propane test-all seemed ok
and tightened intake man bolts to about 15 ft/lbs torque.

26 dec 2005 tested again --results: failed
score:
high speed low speed
std reading | std reading
HC ppm p 162 96 | 167 121
CO % p 1.04 .64 | .94 .59
NOx ppm f 1163 1388 | 1273 1991


Now, I'm getting worried, what to replace? o2, cat? dump the car?

again more work:
*1) new intake manifold gasket from shelf--noticeably oily, poor condition
2) new oil breather, o-ring gasket
3) new water temp sensor to ecu, old sensor still in resistance range--now have spare.
4) put rebuilt 70 amp alternator back on, better charging than old volvo 80 amp.
5) replaced brake booster check valve
6) bought timing light, tach & dwell from ebay,
set timing about 9.5 deg BTDC
set dwell within 20-70 deg
tach about 740 rpms, good enough
*7) muffler shop checked hairline fractures in exhaust pipe--not a problem, but found a hole in pipe on top of pipe where you can't see it, but leaking exhaust deflected flame--patched up.

31 jan 2006, another test, dramatic results
a) waited for cold day in jan to test but warm jan
b) last day before inspection expires.

**1) plugged ignition vac hose to manifold
2) high octane gas
3) cool morning, 45-50 deg ambient temp
high speed low speed
std reading last | std reading last time
HC ppm p 162 18 (96) | 167 47 (128)
CO % p 1.04 .17 (.59) | .94 .46 (.63)
NOx ppm p 1163 380 (1746) | 1273 827 (2161)


Qualitative Conclusions:
1) intake manifold probably a major leak, but probably had few earlier other small air leaks, but i checked manifold leakage with propane test earlier and didn't notice a difference in rpms.

2) plugging ignition vac hose probably highly effective.
3) followed brickboard advice to the letter:
a) if cat not rattling or plugged, don't replace.
b) o2 sensor only had about 40k miles, most likely still good, don't replace.
4) a combination of things helped, not just one single item, but i was able to eliminate possible problems and found new ones. injectors, cat, o2 sensor were all good, so was probably the plugs cap, rotor, but last 3 replaced (cheap)
5) intake manifold definitely toast, probably original.

Can probably pass Cal specs!!

My car's birth: Feb 1986, what a birthday present, happy 20 years & to 20 more. I'm now homing in on a 300k mile badge, please no wrecks.

Hope this helps those who have Nox problems and to give ideas where to start and save headaches & money. these were my problems and solutions.

thanks bb & members for sage advice.

byron golden
86 245
92 245