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Topic Review (Newest First)
03-21-2015 02:02 PM
amc49 It can be either EGR system problems or the front or top half of the cat depending on how cat is mounted. The front section reduces any leftover NOx that the EGR does not treat. If car has a low cat then whacking it against something on the ground can easily shatter the matrix to fail NOx, grab exhaust there and shake it to listen for like broken glass, if so cat is dead. Muffler guy trick is to whack cat with a hammer and tell you the broken sound you hear is a bad cat, well, or course, he just fractured it. How they get cat repairs. EGR itself cools the A/F mix by dilution, the burn is not as hot then and NOx then drops, it forms at combustion temps of over 2500 degrees. Too high compression can make it form too, why all emission engines in the '70s lowered their compression ratios. The average grocery getter engine 10.0-10.5/1 dropped to like 8.5/1.
03-20-2015 06:36 PM
sailor O.P hasn't posted since 6/12, I imagine it was resolved with EGR system repair.
03-20-2015 04:34 PM
herenow Curious on what the resolution was with the NOx emissions issue?
04-02-2012 04:34 PM
SPI Tuner NOX is because you car is getting to hot. The EGR system puts burned gases back in to the cylinder to reduce NOX emissions. So yes you are right. Since I'm guessing you live in Cali the emissions standards take that into consideration. So yeah check you EGR flow with a vacuum pump on the EGR test port. If you surpass 4.2 in/hg of vacuum and the engine doesn't start to idle rough then that is your problem.
03-07-2012 09:04 PM
svtf1417 I could have sworn I learned in class that the EGR system is what helps reduce NOx, oxides of nitrogen, in emissions.
03-06-2012 07:52 PM
High Nox emissions after rebuild

I just finished rebuilding my 2001 SPI after failing my previous emissions test for slightly too much hydrocarbons and dropping a valve seat shortly thereafter.

I had the crank turned, put new bearings, pistons, rings, timing belt, timing component kit, head with hardened valve seats, head bolts, thermostat, water pump, oil pump, and all new gaskets. I cleaned the block inside and out, deglazed the cylinders, cleaned the intake manifold, egr and throttle body. Of course I also changed the oil and filter as well. I have a new radiator, I flushed the cooling system, and I put new antifreeze. Right before it dropped the valve seat I changed the air filter and oxygen sensors.

The car was running somewhat rough at times and seemed sluggish after having done all of that, I ultimately found this to be caused by the original fuel pump module lines being brittle and cracked. After replacing the fuel pump with the newer style pump and replacing the fuel filter, the car is running like it never has.

I took it to the smog station and it failed the functional check for "MIL/Check engine light test due to failure to successfully complete all OBD self tests" which I understand was caused by the fact that I don't have enough drive cycles after resetting the computer. I am not too worried about that.

What concerns me is that it failed the sniffer test as well, here are my results:
15mph FAIL
RPM 1833
CO2 14.7
O2 0.1
CO 0.20 MEAS 0.54 MAX
NO 816 MEAS 467 MAX

25mph PASS
RPM 1759
CO2 14.7
O2 0.1
CO 0.15 MEAS 0.53 MAX
NO 751 MEAS 754 MAX

So far, I have checked for vacuum leaks and I found none, I also checked my pcv valve and it was not clogged, however I did notice that I just barely had it twisted into the hole, so it could have been sucking air from the environment rather than the actual crankcase. I checked the EGR for function by unhooking the line going from the egr regulator and attaching it directly to the egr valve, at which point the idle became extremely rough and the motor died, as it should. I noticed that with the egr regulator hooked up correctly I could not seem to get any vacuum on the line that goes from the regulator to the top of the egr valve, even when I revved the motor above 2,000 RPMs, does this indicate that I have a faulty egr dpfe or vacuum solenoid? I used generic O2 sensors from ebay that I had to splice in, could this be my problem?

Also the engine has less than 25 miles so I don't know it that could be part of my problem. I didn't heat my cat up by driving on the freeway like I normally do right before smog, but my car was up to operating temp.

Any help with this issue would be greatly appreciated! I really need to get this thing back on the road and I would hate to have to shell out the money for a "hot smog" when my car is completely stock and passes the smog test in every other aspect.

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