Old 02-07-04, 11:40 AM
raharold's Avatar
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Join Date: Sep 2003
Location: in the armpit of the nation
Posts: 177

I just got my '95 Infiniti G20 inspected. Part of the inspection includes a high and low speed emissions test on a rolling road. I passed but...just barely. Here are the results:

This Year:
Standard Current Reading
HC(ppm) 136 136
CO(%) .76 .30
CO2(%) 15.0
O2(%) .3
Nox(ppm) 1045 548
Dilution >6.0 15.3
Last Year:
Standard Current Reading
HC(ppm) 136 135
CO(%) .76 .15
CO2(%) 14.9
O2(%) 0.0
Nox(ppm) 1045 69
Dilution >6.0 15.1

I included last year for reference.

I'm thinking next year I won't pass.

What would cause such high HC?

Last edited by raharold; 02-07-04 at 05:46 PM.
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Old 02-07-04, 01:41 PM
Join Date: Apr 2002
Location: Pittsburgh,Pa
Posts: 2,417
I don't know what mileage you have but it seems the major increase over last year was nox.I tend to believe you are building up combustion chamber deposits because of the nox and hc readings.But you may also be running slightly lean.I would suggest cleaning the combustion chambers and fuel injectors then replace plugs and or other ignition related parts and filters.Nox is caused by heat in the combustion chamber due to excessive cooling system temp,over advanced timing (valve or ignition),malfunctioning egr system,lean fuel mixture or combustion chamber deposits causing higher compression.Hc s are unburned fuel due to misfire from an electrical,engine mechanical condition,fuel problem(lean or rich)or advanced timing.I think if you follow my suggestions you will pass with flying colors.
Old 02-07-04, 02:48 PM
raharold's Avatar
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Something I didn't mention before - the car seems to run fine and it has 113K on it.

Last year, It failed the first go round. I replaced the distributor cap and rotor, spark plugs, O2 sensor, replaced the oil, and checked the timing (it was in spec). All that probably helped but I think the real reason I failed was because I didn't warm it up. The inspection station is right around the corner from my house and I drove straight there and turned it off.

I wonder if it could be as simple as the fuel filter as you mentioned? I don't remember ever changing it.

I've never had the injectors cleaned. What type of injector cleaning would you recommend? Removal or on car? I've heard the dump in the tank stuff can cause havoc on the pre-injector fuel system so I'll avoid that.
Old 02-07-04, 10:58 PM
mike from nj
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when i first looked at the readings, i was thinking the cat converter is on it's last leg. any good cat should bring the HC readings down close to single digits. then i read about your 'cold' cat----that has the same affect. it needs to be close to 800-1000 degrees inside to remove all those HCs.

like davo pointed out---your NOx jumped from 69-548. this is a huge jump. i've seen readings around 2000 on cars with clogged or broken(or disabled) egr valves. NOx is also a big 'smog' contributor, and it should be everyone's concern.

a fuel filter or a tune up or an injector cleaning won't fix NOx either(it would probably help with the HC though).

if you have an egr valve, i would first make sure it's working as designed, including the passage which is almost always clogged at high miles.

the best injector cleaning you can get, with the injectors still in the car, is the type where the fuel lines are unplugged and hooked up to a bottle full of cleaning solution and the car is run off of that.

contrary to popular belief, the egr dosen't steal any horsepower from the engine and it DOES slightly increase fuel mileage, why people disconnect it is beyond me.
Old 02-08-04, 04:56 AM
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Both of these tests were with the car fully warm. Do you still think it could be the cats?

It think the car has an egr valve. I'll look into cleaning it. I think there is a How-To for this somwhere on the web.

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