1991 Camy V6 LE Failed Emissions

[91 2VZ]

**Excuse me for the thread title...I meant "Camry" instead of "Camy"**

Check engine light is on for a knock sensor (52) and oxygen sensor (21). Car recently had a tune up which included air filter, spark plugs, spark plug wires, cap, rotor, ignition coil, engine coolant temp sensor and oil change.

Test results:
HC: Limit: 120, Mine: 13

CO: Limit: 0.64, Mine: 0.01

NOx: Limit: 1400, Mine: 2596

What would cause the NOx to be so high while HC and CO are well below the limit? I have like 60 days to fix it. This sucks cause I work and have school 5 days a week and have no other car to drive at the moment. Can't really find the time to diagnose or fix it myself.

Any guesses on the major contributor of high NOx emissions?

[hzt30]

The most probable cause for high NOX is EGR valve system not functioning properly. With engine idling, apply vacuum to the EGR valve and engine should run rough or stall. If it does, then EGR valve itself is working. If not, then EGR valve is malfunctioning. Check for clogged EGR valve, passage ways. Also check the EGR modulator and BVSV valve.

[91 2VZ]

That's strange, the EGR valve was changed a couple years ago with a Toyota unit.

I did have an issue with the BSBV valve when I was swapping out the coolant temperature sensor. I broke off the nipples on it when I was removing the vacuum hoses but I used some replacement vacuum nipples and super glue to temporarily fix it. Maybe that's the issue?

[91 2VZ]

Also, I filled up with Shell's "nitrogen enriched" gas...89 octane right before I went to the emissions center. My question is, can Shell's "nitrogen enriched" gas cause high NOx readings?

[hzt30]

Originally Posted by 91 2VZ

Also, I filled up with Shell's "nitrogen enriched" gas...89 octane right before I went to the emissions center. My question is, can Shell's "nitrogen enriched" gas cause high NOx readings?

It may actually burn cleaner and cooler being nitrogen, which would mean more power.
But don't know if that has a deleterious effect on emissions.

One would think that a major company like Shell has done some extensive testing and research first and found no negative effects before putting it on the market.

If the EGR system checks out OK, another thing to consider is a bad catalytic converter.

[DM89]

The added nitrogen in Shell gas has no affect on NOx emissions. Considering the air going into the engine is 78% nitrogen, the added amount in Shell gas will make no difference. NOx emissions are formed from high temps and pressures. Other than EGR problems, a lean misfire will also cause high NOx.

[91 2VZ]

Thanks for the insights. I'll check out the EGR valve whenever I'm free from work and school. Also, I'm also going to try and get a new BSBV valve. I have 60 days before my re-test date.

[Doctor J]

You may need to check knock sensor and O2 sensor as well.
Check the vacuum hoses to EGR
vacuum hose ports on the throttle body