Hi ,
my 6 cylinder 1994 XJs failed smog only due to high HC at 2500RPM. At idle the
Hc is 63 , 80 was permitted, at 2500 rpm Hc was 68 , only 45 allowed
co2 is 14.9,
o2 is 0.0,
co is 0.06 at idle, and 0.16 @ 2500 rpm
NO is 7 at idle and 1 at 2500 rpm
new sparkplugs , cleaned distributor contacts,
1 year old sparkplug wires,
o2 sensor has 4.2 ohms on heater wires
vaccum seems good on EGR valve,
before smog I drove like Andretti , fast and furious,
no codes ,
Apologies for noob question - is that an idle only or dyno test?
From the law of physics:
tyre size (weight) and pressure will make a diference if that’s a dyno test (just ask car manufacturers, their certification cars are doubled on max limits)
again - if dyno test - auto gearbox condition also matters (should be burning hot, and kept running in D before the test)
spark plugs - can be new and you’ll assume these are ok, but the gaps on new plugs, even branded… Oh dear (gap variation will unbalance combustion/exhaust by tiny amount
take out the air filter entirely for the test time, remove that squashed plastic air uptake bit - if you have one.
as mentioned by Vee, old lambda can give you some wider range, but can be checked
high mileage may suggest oil burning, if so - make sure you have fresh one, fully synthetic in your engine prior to performing testing.
how old is your fuel in the tank? Are you driving the tank out each month? Each week? Living in humid area? Was your tank topped up full prior to test or was it half empty? What fuel you’re using?
what’s the max limit on O2 during the test? You may be able to drop HCs at 2500rpms (only at 2.5krpms) with addition of magical octane booster or lab grade ethyl alcohol (just saying…)