cant smog my 1994 gmc truck

Asked by Nov 12, 2014 at 05:47 PM

Question type: Maintenance & Repair

I have a 1994 gmc 1500 sl with a 4.3 and 5 speed manuel trans it has 333942 miles but
runs like a champ I went to smog it and it failed in nox at 15mph it was 650 max is 500 at
25 mph it was 1091 max is 754  my cat conv is only 4 years old what to do louie

1 Answer


That is a lot of mileage for a 4.3, you must take care of it, have you had the codes checked? There could be some stored in memory that will steer you in the right direction, could be an O2 sensor just out of specs but not open or shorted so it won't turn on the check engine light. Might do a compression test just to make sure the compression is good and not too low.

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