Emissions

[doctor_masterson]

I am helping my grandma by working on her vehicle. It is a 1990 Buick Le Sabre. It did not pass emissions due to a high NOx exhaust measurement. I have thus far replaced the PCV valve and the air filter. The air filter smelled like oil, although it appeard to be relatively clean. The PCV valve was quite oily. Please help!

[RABarrett]

High NOx emissions are the result of excessive combustion temperatures. Typically, it is the result of EGR problems, or control of same. In some situations, the problem is the result of clogged EGR lines. Likely, yours is the electronic type. It will require some troubleshooting to resolve. New ones are expensive. Ray

[edg]

My '91 Buick LeSabre failed the emissions test with high NOx. The HC and CO passed.

The solution was to remove and clean the EGR valve. Two bolts hold it to an adapter on the intake manifold that has a corrugated tube running down to the exhaust pipe. Perhaps luckily for you, 87-90 Buicks are equipped with an EGR filter between the exhaust pipe and the valve. It's purpose is to reduce the carbon buildup, so you may just need to replace the filter instead of cleaning or replacing the EGR valve.

The EGR valve itself is a 3 orifice digital unit, and on my vehicle all three orifices were about 1/3 restricted by carbon. Also, two of the plungers had carbon buildup above the pintle that limited how far they could open.

I disassembled the unit by removing three Torx screws holding the solenoids to the base plate containing the orifices. Then I cleaned the orifices and solenoid plungers with alcohol (don't use carb cleaner or solvent; it can damage the solenoids) and some careful scraping with a small screwdriver and several Q-Tips. I sprayed Protek ProLube on the plungers to lubricate them. You could also use a Teflon spray, such as Elmer's Slide-All. Do not use oil or WD-40 or grease as they will attract dirt and cause the plungers to stick.

Finally, I reassembled the unit and tested the operation by providing vehicle battery voltage to each of the 3 solenoids in turn though jumper wires. (See Wells CounterPoint "Diagnosing Digital EGR Valves" article for more details.) All 3 audibly clicked open. I had the vehicle retested and it passed.

A replacement OEM EGR valve runs about $275. An aftermarket replacement from Wells Manufacturing (available at AutoZone) is about $165.