Failed emissions, NOX high, ONlY at 25mph

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When my 91 626 failed NOx 9 months ago it turned out to be a small leak at the exhaust manifold. Once it was taken care of the NOx levels were back to normal right away.
 
We had the daughters car fail for high NOX. She always did short city trips stop and go.
I added a strong fuel cleaner to the gas, seafoamed via brake booster and took the car for a 3 hour round trip highway run. Ran the tank down to about 1/4 topped it off with high octane fuel and passed by a wide margin.
 
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Originally Posted By: cjcride
We had the daughters car fail for high NOX. She always did short city trips stop and go.
I added a strong fuel cleaner to the gas, seafoamed via brake booster and took the car for a 3 hour round trip highway run. Ran the tank down to about 1/4 topped it off with high octane fuel and passed by a wide margin.


For decades we were told to run the car hard then take it immediately for inspection, idling as little as possible. Now in NJ if your vehicle is OBDII, usually 1996 and newer they just check for check engine lights and plug into the OBDII port to see if there are any pending codes. If not you're good to go. They don't care if your tires are bald, have no brakes, wipers, lights, etc. All they care about is the emissions. Of course the police will ticket you for those safety violations.

Whimsey
 
CA changed too just a year ago.
Only 2000 and older now require the dyno*.
OBDII for everything else



*plus a small percentage based on heuristics and to establish further testing
 
I suppose I should provide an update. I did all the "cheap" fixes suggested - front and rear O2 sensors, plugs, wires, air filter, fuel filter, seafoam in the gas tank, seafoam in the brake booster, water in the brake booster, and a can of guaranteed to pass. Took the car back for a retest today, and it passed with NOx under 20 at both speeds.
 
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