Have a 98 Blazer LS 4x4. It burns really rich, you can smell it right off the bat. The exhaust rattles, like inside the muffler. Has troubles starting up after driving for a couple miles. When it does start it just bogs and finally turns over into a rough idle. If the car idles in Park for over 5 minutes the service engine light comes on. Just wondering if there could be multiple problems or maybe just one source. Thanks a lot!!

 

Did you get the code read? I would start with a fuel pressure and leakdown test.

 

Sounds like your cat is bad, also. The rattling is a dead giveaway.

 

Agreed, it sounds like the cat is bad but you need to figure out what killed it first. Usually running rich is what does it. Without fixing the rich condition you will only destroy another cat and you probably have pretty bad fuel economy right now.

 

Thanks for the tips guys. Was leaning towards the cat. I just had the fuel pump replaced last year. I noticed the rich burning in the spring around March. What usually causes it to burn rich? Sensors or something?

 

A number of things, the two most likely are either a leaking fuel pressure regulator or leaking injectors. You can look down the passenger side of the throttle body. If it looks really clean and shows signs of washing then you know you have a leak.