FAILED Emissions Test :(

Original converter? Probably getting tired...

Had a 4.3 S-10 Blazer that had that trouble. The tester told me to take it out on the Interstate and get it hot, and blow it out. I did and came back, and it passed HC with numbers to spare. Andy

He's right, and your CO% at idle is somewhat higher than it ought to be, too, though it's fine at speed. High HC *with* high NOx often indicates oil burning, though it can also indicate excessive carbon in the combustion chambers and/or a faulty EGR system in combination with an overly-rich mixture caused by any of several factors (improper values being given by the MAP, TPS, O2S, engine temp or other sensors; leaky fuel injector(s). It can also indicate vacuum leak(s).

It can also indicate an inefficient catalytic converter. Replacing the converter will often knock the numbers down enough to pass the test, but if there are underlying causes of the high numbers, the condition will return.

Time for some systematic diagnosis, inspection of the entire EGR system, evaluation of oil consumption, etc. Guessing and throwing parts at it is an expensive way NOT to fix the problem.

-Stern

I thought I would post a few more things that might be better clues as to what's going on:

1) Four times in the past month, I would go out to start the car, and it would crank but not "catch" and start unless I stepped on the gas pedal and opened the throttle. If I did start it this way, the RPM's would jump all crazy...going from almost ZERO to 2000 RPMs. I could cure the problem simply by shutting the engine OFF and re-starting it!

2) Via my AutoMeter Vacuum Gauge, I can see that sometimes at idle, the vacuum is a solid 15" hg(in Drive), and other times, especially when HOT, the gauge will fluctuate slightly between 13.5" hg and 15" hg. I read online that this is usually a spark plug gap problem or ignition related.

3) Once the engine is up to operating temperature, I can view my Air/Fuel Gauge(LED based), and watch that as I am slowing down and coming to a STOP, the O2 Sensor(NEW) will stick RICH, and sometimes not move from the RICH for up to 1 minute while idling!

So, I think #1 is the most important. Especially if we can assume that the fact that the engine is definately running RICH is RELATED to the fact that sometimes the engine won't start unless the throttle is opened. And anytime the RPMs are going *crazy* and the tach is jumping all over the place and causing surging, simply shutting the engine OFF and re-starting it somehow CURES the problem!??

Knowing this, could it possibly be a bad MAP Sensor? I know that the MAP Sensor tells the ECM the outside barometric pressure, and if it was telling the ECM that I was at a much higher altitude than I actually am, I believe the engine would not start?

Given this information, is there anything else that can be added? I am going back on Monday to get stuff diagnosed, but I would like to have more info going in...