For the last 6 months my burban hasn't been running good at higher speeds (70) and the last few days when i would pull up to a stop sign and stop I could smell exhaust. Last night on the way home the check engine light came on and blinked then stayed on. For the last 6 months when you try to pull a big hill lets say with the cruise on and you really load the engine the check engine light would come on and blink and go back off. I have had it checked a month ago with a complete diagnostic check and they couldn't find anything wrong. Any ideas? I am about ot leave and have the simple test done at Autozone since the light is still on. Any help would be greatly appreciated.

 

MAybe clogged catalitic converters.

 

Have you replaced or checked your Oxy-Sensors. there is 2 before the Cat and two after the Cat. When these go bad they give the symptoms you are describing. one or two of your Oxy-Sensors most likely before the cat is intermittent. this is why your smelling exhaust fumes. Sometime they will throw a code sometimes not, because they never completely fail altogether. You could have an emissions test done for about $17 bucks. figure out the RPM for 70 mph and run the engine at that RPM during the test.