I just went through the 'stealership' experience my self. Some how a new Mopar oil filter got on the car (Dodge Dealer), but when I changed the oil 150 miles after I bought the car it was jet black, and the oil that is in there now looks as good as I put it in 2000 miles ago. Also mine came with a Tranny that only lasted 300 miles, luckilly they had to fix it costing them about $1500 for a GM refurbed tranny and installation at the GM dealership.

I would look at the plugs first. Aparently a classic problem is to set the gap wrong. Like a Camaro with TPI needs one spacing, while the carbed version needs something different. Also it should be noted that Platnium plugs are really good, just not in your car. My understanding is that the AC delco plugs are the way to go.

I have seen this problem in a Tacoma, Defective (third party) wires from the factory. Quality issues happen when people cut corners to try to save a buck. Anyway, This will make the cylnder not fire at all and drop gas mileage by approx 35%. About the only way to test the wires would be to pull them and check with an ohm meter. Usually the crimp from the wire to the lug is not well made and sometimes when you pull the wire the lug will stay on the plug. I wouldn't know if it would throw a misfire code or not. While you are here you may want to verify the firing order is correct. You will need the Chilton book or Chevy service manual to figure that out though.

Speaking of codes and code readers, You may want to have your codes read out of the computer. Unless they were specifically cleared the codes should be retained even though the 'Check Engine' light is not on.

Depending on how 'back-yard mechanic' the dealership is, the common fix for a recurring 'Check Engine' light is to either remove the bulb from the holder or leave it in and cover it with electrical tape. This is the local Ford dealerships specialty. Anyway, When you turn the car on the instrument cluster should light up like a christmas tree. Compare the lamps to the instrument cluster diagram in your owners manual (if your dealer ship didn't throw it away like mine did). About the only thing that won't light is the turn signals and you can test those with the hazard button.

Manual for 2000 Chevy Blazer

Autozone will read the codes for free, or you can invest in a OBD-II code scaner. Buy the cheap one as all the $150 - $200 models do is tell you the fault on the display and the cheapies have a look-up book. It takes a really expensive ($2K) one to read the airbag and extended codes, so you can save some coin.


Almost forgot...

If this is a 4X4 version, your front axle may be engaged. Verify this with the 'Waldo Check'. Go to a empty parking lot, put the wheel hard over and drive a donut. If the front tires are screaching to a degree, it is engaged. This can also be preformed to verify that the 4X4 section of the transmission is functional during test drives.

 

Thank you so much, thats a lot of information that I can really use. I will start going over the engine and stuff. Is it possible one or two cylinders are not firing? Wrong spark plugs?

 

I'd check the wiring first. It could be as simple as when the dealership replaced the wires they didn't get a 100% connection between the wire and plug. The same also applies from wire to distributor so be sure to check both ends. Also you may hear a 'miss' if this is the case. I am an electrical engineer by trade so I am not really up when it comes to engines.