Please help interpret my smog check results

[bgilly]

I just picked up my '94 Q45 Saturday, and I'm loving it so far. Here are the smog check results, I'd just like to compare it to others to get an idea of how the car's smog & other systems are functioning:

15 mph - %CO2 = 14.4, %O2 = 2.24, HC (PPM) = 15, CO(%) = 0.00, NO (PPM) = 42625 mph - %CO2 = 14.4, %O2 = 2.10, HC (PPM) = 11, CO(%) = 0.00, NO (PPM) = 412

It did pass, because all these readings are below the allowable maximums, but I'm a little concerned that the NO readings are the only ones that came out higher than average (avg = 150,136 for 15,25 mph respectively). This is an overall well maintained car with only 78k miles on it.

Thanks in advance for any help.

[sultan]

was the car fully warmed up when it was tested? if it sits a while the cat will get cold and you will get higher readings. it could be your O2 sensors, or bad gas (or too low octane). for comparison here are my recent numbers from inspection in January. i also have a 94, had 123,026 miles, and probably the original O2 sensors (i have new, haven't changed yet)15 %CO2=14.9 %O2=0.0 HC(PPM)=14 %CO=0.00 NOx(PPM)=725 %CO2=14.9 %O2=0.0 HC(PPM)= 9 %CO=0.03 NOx(PPM)=8

[DAEDALUS]

A couple of usual suspects for high NOx are high combustion chamber temps and bad catalytic converter. The cats rarely go bad, and if they were bad, I think your HC and CO readings would be higher. High combustion chamber temps can be caused by several things...running too lean, bad cooling system (overheating), poor timing, bad O2 sensors, clogged EGR system.

[Q45tech]

The EGR passages get dirty [by 60k] and clogged [partially clogged] up reducing the oxygen poor exhaust gas recirculation...........always the problem with high NOX reading! Get everything cleaned. Will need a roto rooter type cable cleaning and some disassembly!

Common problem on all cars makes and models.......why most 2003 models are going to full VVT to do away with EGR and the problems it causes prior to 100k.

Why are some worse than others [driving style and conditions].............lots of short trips [cool weather] fails to heat up the EGR system and the junk condenses eventually.

A 9-10 year old car driven in LA traffic only 74k is a prime example.

[bgilly]

sultan: to be honest, i don't know if it was warmed up or not, because the seller smogged it. thanks for posting your numbers, that's exactly what i was hoping somebody would do!

DAEDALUS: Hey, isn't your email name spelled differently? hahahaha Well, how much do you charge for such a cleaning as prescribed by q45tech? I imagine that involves plenum removal. I am having the passenger side valve cover gasket replaced within the next few weeks by the Infiniti mechanic that I bought the car from, maybe I can have the plenum & EGR passages cleaned out while he's in there. If I'm lucky, he'll even let me come clean it myself while he's got it all apart. That would be nice.

Q45tech: Thanks so much for the info and for narrowing it down, this really helps me get started in the right direction.

I guess the next thing will be new O2's! Do you guys think cleaning the EGR & plenum will improve gas mileage at all? That would sure be nice!

[Q45tech]

Probably not ...........x amount of air need y amount of fuel, now bad O2 can increase consumption by zero to 20% at cruise.

Your California problem is the fuel itself and its 5-10% lower BTU which means you gotta burn 5-10% more to create the same power.

Cleaning just get things back to normal and frisky.

[DAEDALUS]

Bgilly, yes, my email addy is a bit different. Someone had snagged it already when I signed up! The EGR job doesn't require plenum removal. In fact, I pretty much doubt that your tech will have to remove the plenum to reseal the valve cover. And the EGR is on the driver's side, but no harm in asking. Should be pretty easy for someone with his experience.

[bgilly]

Well, actually you're right, he wasn't going to remove the plenum, just raise it for clearance. I was going to ask him to remove it so I could clean everything. But since I don't have to have him do that, that's even better! I'm gonna go outside and have a look at where its located right now. I can't wait til I get the shop manual for this thing, that will be so nice!

[bgilly]

UPDATE: OK, it's only taken me 4 months to finally get around to pulling the EGR off to clean it. It was clean! No gunk in there at all, not in the valve, the metal tube to the exhaust, or the intake manifold EGR port. So now I'm confused about those high NOX readings.

[Q45tech]

Somebody cleaned it looking for the NOX problem. OR the EGR is not working and thats why it is clean............check the system manually at idle make sure moving the diaphram up with finger causes the engine to stall, then check vacuum lines and ports solenoids and EGR temperature sensor...........use Consult to force egr.

[bgilly]

OK I checked the EGR manually and the car did want to stall. Vacuum lines all look brand new. How can I check the EGR temp sensor?