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Black Smoke and Check Engine Lights, Oh my! Hi. I have a 2005 Avalanche with a 5.3 Vortec engine, automatic transmission. I went on a road trip from about 6300 feet and went to northern Idaho, thru mountains, and ended at around 1400 ft. (Up and down trip). Then on the way home, some 1200 miles later, my engine kind of stumbled at a gas station, at idle right before accelerating. I didn’t notice any reason for it, and runs super while driving. Now it is real bad! Blows black smoke, and stumbles badly. Check engine light is on with engine code of random misfire (PO300). What do you suggest I do? Jerry

Jerry, Get it looked at by a pro A.S.A.P. I suspect the O2 sensor may have died or some other sensor that affects the power train fuel control. Just find a good shop with a Tech 2 Scanner (OE type scanner) and let them figure it out. We know it is running rich! The question is, why at 45K? Seek help soon, before you do serious damage to the catalytic converter. The good news is, if the cat converter is damaged, it is covered for 8 years or 80,000 miles by the manufacture. Hi, I found your site ( while searching for information on a problem with a 1994 Olds Cutlass Supreme (3.1 L engine). The car works fine around town, but when driven above 40 or 50 mph the Service Engine Soon light comes on. The light stays on until the engine is shut off and doesn't come on again until the car is again driven above 40 or 50 mph. Since the light comes on, the car is rarely driven on faster roads, but when it is I haven't noticed any difference in the way it runs or otherwise performs. No other warning lights come on. I can start with a completely cold engine drive under a mile to a 50 mph road and by the time I reach the speed limit the light is on. Greg Take a paper clip and make in the shape of a "U" then place it in the DATA connector under the steering wheel. (That is the connector you plug a scanner into.) Turn the key on and count the (check engine light) that is flashing. It will flash one long flash then two short flashes this is a code 12. Ignore that one. I suspect it will flash a 32 which points to the EGR system. This is very common problem on older model cars when your car is at sustained highway speeds. If it does flash a code 32 then the EGR valve may be defective, unplugged, or the passageway may be clogged. This WILL affect your fuel mileage. James Tip for better fuel mileage: If your car has a mass air flow sensor (most of today's cars do) Clean the Mass air flow sensor with Aerosol Mass Air Flow cleaner every time you change your oil. It is money well spent towards keeping your car running well.


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