PlotPoint

Not the fuel pressure regulator, but a fuel damper (dampener?) One mechanic said replacing a leaking fuel damper could definitely help with reducing high NOX on emissions testing. Second mechanic said "meh", or, in other words "not really". Kind of makes me wonder who knows what! Please let me know what you all think.

sndlight

Only if it is causing a lean condition. Do you have a check engine light on?

PlotPoint

One of the causes of high NOX is a lean condition (the most common cause of high NOX from what I have read). And on my last smog check two years ago, I got a very high NOX reading (barely passed). Though the check engine light never did come on.

How bad would it have to be before I got a check engine light? Is that triggered by hot engine temperature?

A lean condition means the engine is running very hot...

dicer

And why would a lean condition mean the engine is running hot? All diesel engines run at a lean condition especially at an easy cruise condition. Combustion can be hot to a point when lean in an si engine, and doesn't mean the engine is running hot. Past that certain point the excess air will cool it like the diesel.

PlotPoint

Dicer -- Not sure. I am not a mechanic, or even a DIY, and my info comes from canvassing websites for information that will help me solve the high NOX issue. From everything I have read, a few of the culprits for high NOX are lean condition, defective egr system, or defective catalytic converter. I have read here that the catalytic converters seldom go out on these cars,and my egr system tested fine, so that left me with "lean condition".

Here's one of my sources:

"Lean Fuel Mixture - Lean fuel mixtures cause high NOx. A lean fuel mixture exists when less fuel then required is delivered to the combustion chambers or when more air then necessary is added to the fuel. In either case the lack of gasoline needed to cool the combustion chambers down is not present. Combustion temperatures increase causing high nitrous oxide emissions. A lean fuel condition may be due to a vacuum leak/s and/or defective fuel control components, such as the Air Flow Meter, Engine Coolant Temperature Sensor, and O2 sensors."

http://www.smogtips.com/failed-high-...rous-oxide.cfm

The high NOX results when engine temps reach above 2500 degrees Farenheit (what I read).

By the way, I passed the smog check (yay!). The NOX was below the limit considerably on the pretest, then on the actual/final smog test 5 minutes later it was quite a bit higher, but still well within limits. So it's possible (likely?) that fixing the fuel leak (replacing the fuel damper) also fixed the high NOX.

I did a pretest and it passed, so I told them to go ahead and do the final. The NOX was 337 at 15mph and 365 at 25mph and the max NOX allowed was 448, so well within limits. I did not even bother with doing the "hard drive" on the freeway this time, but did drive it in low gear the 5 miles to the shop with some speeds reaching 50 mph. New oil, new air filter btw. The car sat for 15 minutes (idling) before they could get it in for the pretest. It sat another 5 minutes (turned off) between the two tests. On the final, the NOX shot up from 337 to 403 at 15mph, and 448 at 25mph (max allowed is 481 so I was still OK). This time, it barely passed due to hydrocarbons It was right at the limit. One more digit and it would have failed. Clearly, more research is needed. :-)