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Failed Smog Test
 

1994 Toyota Camry High Mileage Failed HC and NO

My 1994 Toyota Camry failed the smog check as follows:

Failed 15 MPH HC Max 61, Meas 69.  Passed 25 MPH HC but barely Max 52, Meas 52.

Failed 15 MPH NO Max 701, Meas 720.

The smog check technician said that my timing was perfect as per specs for this 1994 Toyota Camry. My regular mechanic who did the last tune up on the vehicle prior to my last smog test 2 years ago said that my vehicle was not due for a tune up according to the specs for the spark plugs installed, etc.

My car barely passed the 15mph NO test 2 years ago. My preparation for this years test were limited to use of the cleaning treatment Seafoam as per the instructions in the crank case, gas tank, and through the brake booster vacuum line. After adding to the crank case, I drove for about 40 miles then had an oil change. The oil in the vehicle was not scheduled for a treatment at that time, and the mechanic said the oil that was drained was black indicating the Seafoam had definitely done some cleaning.

I took note that prior to going for the smog check that the new oil had gone from almost clear on the stick to a light amber color, indicating some mixing with the old seafoam treated oil residue still in the engine. The gas that was treated with seafoam I ran until almost empty and then prior to going for the test I filled the tank almost full with 91 octane.

I drove about 20 miles prior to the test on the highway. My car sat for approx 15 minutes prior to being tested. Any suggestions would be appreciated. Thank you.


Answer:  

Look at your Toyota Camry's CO emissions as well. Even if they've passed it doesn't mean CO is correct; CO might be low and your Toyota's engine be experiencing a lean fuel condition. A "lean" running engine will cause high HC and high NOx.

The number one fault that causes high NO is a defective EGR system, so inspect your Camry's EGR valve, transducer valve and EGR passages for obstructions and proper function. It is not uncommon for a vehicle with high mileage to develop carbon buildup within the EGR passages. The EGR valve might be functioning but barely, or might not function at all. Use a service manual and diagnose the EGR system for proper operation.

The transducer valve on Toyota Camry's are known to go bad over time. A narrow passage in the transducer valve which is connected to the exhaust manifold and receives exhaust back-pressure typically gets plugged up with carbon and stops the EGR valve from opening.

If the EGR checks out ok move on the the fuel feedback system to ensure air/fuel ratio is correct and the engine is not running lean. NO is created when combustion temp rise above 2500 F. Any engine condition causing increased temps will increase NO emissions.

Once fuel control is established and CO is normal, HC emissions will decrease as well.


posted by SmogTips Support
 


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