high emissions both HC and NOx

Sep 01, 2008 4 Replies
N

How can it be that CO is low but both HC and NOx are high?


81 VW Scirocco with 255K mi. Since last check, car only driven 3300 mi short trips.


1st check: Initially low CO and NOx but high HC.



Changed oil from 20W/50 GTX to Mobil 1 10W/40 High Mileage. New spark plugs. Drove about 150 miles with hopes of cleaning carbon.


2nd check: Both HC and NOx high, with HC higher than before.

Gave the car to a mechanic who previously had gotten the car to pass. Could not find anything out-of-spec (but he has no exhaust gas analyzer).


3rd check: HC and NOx gone up into 'gross polluter' numbers.

Mechanic and smog checker now recommend new CAT and O2 sensor.



Comments?



Thanks, nf


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N

Forgot to mention that mechanic said there's a slight vacuum leak around injectors but not enough to account for high NOx.

Also: this engine does not have an EGR.

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M

The vacuum leak wll make it run too lean, causing all your bad readings.

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S

If this is the case, you can't trust anything. Get the vacuum leaks fixed and try again.

--scott

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B

Get the car to a good tech with a 5gas analyzer and Bosch experience. You'll probably end up needing injector seals and a readjustment of your FI (takes a long 3mm allen) to get the co down, and if there are no misfires and the timing and compression are good the HC should follow. It may end up needing a cat and a 02 as well to clean up that worn out old car. HTH, Ben

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