> One guy: "Yes they do. In fact most vehicles since about: 1988 have > them. It is usually a function of oil pressure, meaning that if oil > pressure drops below a predetermined level (usually about 6-8psi I > think) it will cutoff power to the fuel pump." >
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Apparently you must be one of those novice ignoramuses who just doesn't understand how and realize why sham "experience" so easily trumps fundamental tenets and documentable facts.
if the sensor was faulty enough to give you bad smog, you'd very likely get a check engine light. voltage testing of sensors is a crap shoot unless you've got them on a scope. and even then, the computer isn't looking for voltage, it's looking for the stoichiometry point, and thus the injection percentage that flip-flops sensor readings between high and low voltage, not voltage per se.
high NOx is usually either lean combustion or bad cat. maybe, if you have some badly clogged injectors, some injector cleaner will help reduce lean combustion and thus NOx.
but much more likely, you've got a cheapo cat and it's simply worn out already. platinum is really expensive. used oem cats have scrap values of up to $100. if you're buying an aftermarket cat for $130, you can figure that there's not a lot of platinum or longevity in the thing.
Was NOX the ONLY high item or just the only one over the limit? Without seeing the trace it is difficult to pinpoint the problem, but here are a few items to check before you get panicked.
Check the EGR system ( EGR valve, EGR solenoid, Transducer and Temperature sensor), and vacuum lines for leaks. If the EGR isn't operating it can cause high NOX due to the increased combustion temps.
For the EGR valve you apply 5-10 in.hg of vacuum and watch the valve. It should open and hold open until you release the vacuum.
Testing the solenoid is a bit more involved due to the three lines. You should have two lines in an L shape on one end and one straight out the other. You need 12 volt power and either vacuum or air pressure. With NO power applied the L shaped port should allow air through either way, with none going out the straight port on the other end. With power APPLIED the air should NOT flow through the L shaped port like it did before. Now the air should go through the port on the other end and the port sticking out the side of the L shaped port.
The transducer gets tested by plugging one of the ports on top. Now blow into the bottom port gently while applying a vacuum to the unplugged port on top of the valve. While you blow into the valve the vacuum should hold steady. When you stop blowing it should open and allow vacuum to pass through. DO NOT USE AIR PRESSURE TO BLOW INTO THE UNIT. It operates using exhaust pressure and higher pressures will damage the diaphragm inside the unit.
Temp sensor is a simple unit. Should read high resistance when cold and much less when hot. At freezing it should read 7.5 up to 10 meg ohms. With it at the boiling point of water it should read (POINT) .20 meg or less.
Check for vacuum leaks below the injectors (this will usually show up with a slightly high idle speed as well but may not), ignition timing, excessive carbon in the cylinders, look at the exhaust for leaks before the cat. Check for anything that could be causing a lean condition.
Even using cheap gas could cause problems. What I do with a marginal fail is tell the owner to fill up with higher octane fuel, then take the vehicle out and run it HARD for a few miles, make sure it is up to temperature and everything is working. Do this a few times then bring it back for the retest (if it's a close test I'll toss the 5 gas tester on it prior to the test as a precaution) This works wonders on the grandma cars that set around and hardly get brought up to temp.
There is a leak in the Transducer between the line to the egr valve and another 1 going to the tee fitting on the Transducer. (EGR valve itself works fine) Can't find the part online so probably horribly expensive. I am thinking of bypassing it and running vac direct to the EGR. Will try to disassemble it and repair 1st.
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