Failed Emissions, NOX too high

[Mgottli]

I recently took my car in for emissions (1986 Tercel 4wd Station Wagon, Automatic) and it failed emissions. It was .29 grams too high on the oxides of nitrogen for grams/mile. Any idea what I can fix or where to start to make it pass?

[Petros]

Welcome to the forum,

Sorry about your trouble. It might be running too lean which I think would cause high NOx emissions. make sure there are no vac leaks, all the vac hoses are routed properly and are not cracked or damage. Use the vac diagram for your car (from the servcie manual available for free down load from this site in FAQ section).

[Mark]

The Exhaust Gas Recirc system I think is supposed to reduce this. The EGR vacuum modulator diaphragm often fails causing the EGR valve to not open. I thing the 5 degrees BTDC ignition timing (slightly more retarded than ideal for efficient combustion) might reduce NOX as well. Many people set their timing for 10 degrees for better power and efficiency. You might check this and set it back to 5 degrees if necessary.

[Mark]

I think NOX is caused by high combustion temperatures (which logically are good since that means you are getting the most heat energy out of the burning fuel). EGR replaces some of the oxygen in the intake air with exhaust, giving you a crappier burn and lowering combustion temps so NOX can't form. I read in a old magazine (Popular Science? Popular Mechanics? I can't remember which) that they suggested to reduce NOX readings by as much as 30% during emissions testing, show up on a rainy day since the moisture in the air reduces combustion temperatures. I wonder if putting a small wet sponge in the air intake housing just before the test would have the same effect. As long as it doesn't restrict the airflow, which would make the fuel-air mix too rich and increase CO readings.

[Mgottli]

Thanks for the answers. I'll look at all the hoses and make sure they're all in place. In regards to switching back 5 degrees what am I switching back? The timing belt?

[teranfirbt]

They're talking ignition timing. You'll need a timing light and a 12mm wrench. Timing procedure is to pull and plug (golf tees work well) the vacuum lines going to the distributor (mark them somehow to make sure they go back to the right place). Then point the timing light at the top of the crankshaft pulley with the engine idling. There's a little notch in the crack pulley that lines up with markings on the plastic cover behind it, this shows your base timing. You want it set to 5 for emissions, 10 otherwise. To change timing, loosen the 12mm bolt that holds the distributor to the cylinder head and rotate the distributor until the notch on the crank pulley lines up with the 5 mark. Tighten the bolt to 12 ft lbs, reconnect the vacuum lines to the distributor, and you're good to go.