Sounds like a classic "It passed when the timing was off... Shouldn't
emissions get better with the timing correct?" situation. Your Chevy's
ignition timing should in fact be set to 0 degrees also known as Top Dead
Center (TDC); with the in-line grey & yellow spout connecter disconnected.
During the first smog check, ignition timing on your Chevy Suburban was set
to 8 degrees Before Top Dead Center (BTDC) actually making the timing
retarded. When a vehicle's timing is retarded it lowers cylinder
compression, lowers combustion chamber temperatures, lowers engine
performance and power, AND also lowers emissions; under light load and no
load conditions... And so your Chevy passed the emissions portion of the
smog check but failed the ignition timing part. This is why the smog
inspection process checks both emissions output and ignition timing. For
those who know, it would be too simple to retard their vehicle's ignition
timing and pass the smog check.
I'm afraid at this point you will need to have a certified smog check repair
station conduct a hands-on diagnosis with the ignition timing set properly
to find out why your Chevy failed the smog check. The reasons it failed can
be many and there is no way to tell which emissions part is defective nor
how much it will cost to get fixed. I recommend you use our online VIR
diagnosis system to have one of our smog technicians give you a better idea
of what your Chevy's problem might be. If you used a SmogTips.com certified
smog station for either of your first smog tests, our online diagnosis is
free. Go to www.smogtips.com/smog_evaluations.cfm.
