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91 Camry, re: Unusual emissions, High NOx and High 02, Help please

I recently failed my state emissions test. I drive a 91 Toyota Camry with 190k miles. Here are my results

High Speed (25mph)

Pollutant Standard Current Reading Result

HC (ppm) 123

26 Pass CO (%) .69 . 13 Pass CO2 (% ) 14.6 O2 (%) 19.7 NOx (ppm) 878 1093 Fail

Low Speed (15 mph)

HC (ppm) 128

127 Pass CO (%) ,71 . 31 Pass CO2 (%) 14.4 O2 (%) 20.4 NOx (ppm) 970 947 Pass

As you can see from the results, I failed on the NOx and was very close to failing on HC at low speeds. What particularly puzzled me was the high O2 readings. I looked at the results of my tests for the past 5 years and I have never had an O2 reading over 1%. What is going on here? Was it a malfunction of the test??

I should also mention that before taking the test I did all of the usual things to prepare for the test:

  1. spark plugs have less than 2 k miles on them
  2. changed oil and filter
  3. changed air filter
  4. checked spark plug wires and distributor cap for leaks
  5. checked egr valve for proper functioning
  6. checked compression. 170 - 175 psi on all cylinders.
  7. drove the car for 15 minutes on freeway. Left the car idling before test.

I would appreciate a few thoughts about this problem. Thanks.

Reply to
alkon
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The increase in O2 readings is probably a failure of the lambda sensor. It's the sensor ahead of the catalytic converter (there are usually two) one ahead and one after the cat, usually screwed into the exhaust pipe or manifold. That's it's job, to sense the O2 content, speak to the computer and adjust the air / fuel ratio. Your other problem of high NOx is probably cat related. The first stage (called the reduction catalyst) rare metals (platinum and rhodium I think) are probably breaking down and you may need a cat replacement. Make sure your mass airflow sensor (hot wire) is clean as well, and the EGR valve is functioning. Good luck.

Reply to
user

A second thought is to first remove the O2 sensor and check if it is coated with buildup. That alone can indicate faulty readings to the computer. If it is, it can be easily removed, usually with a clean cloth and carburator cleaner, re apply anti seize to the threads and re install. That's the cheapest way first. Sorry I didn't think of that in my first post.

Reply to
user

Ph@Boy's advice is good.

You mention that you checked the EGR valve for proper functioning - how did you perform the check?

Reply to
Ray O

1) You have low miles on the spark plugs but are they high quality plugs? Do you have NGK or Denso Platinum or Iridium plugs? If not, change them with the aforementioned plugs. 2) You checked the spark plug wires and distributor cap for leaks but are they aftermarket or factory ones? How old are they? If they're aftermarket, replace them with factory ones.

I've seen plenty of Toyotas fail due to supposedly high-quality cheaper alternatives on both situations above and saw them pass after replacing them with factory ones.

3) Letting the car idle for over a minute is not beneficial before the test. 4) Are you sure your themostat is working properly?
Reply to
Viperkiller

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