i have a 1992 k5 blazer. the truck has 99000 miles on its original engine. I just installed a brand new battery with 875 cranking amps. I purchased the truck in oct of 08. I dont know when the last time it was tuned up, or if it has been tuned up at all. when i try to start the truck, the fan blade turns very slow. the last time the truck was running (about 2 months ago) it was backfiring and the exhaust smelled like gas.I need to get an idea of what is going on before i have it towed to the shop so they wont tell me just anything. all comments are welcomed. thanks for your help in advance!!!!!!!!!!

 

Could be a number of different things. A vacuum leak, timing adjustment being off, a problem with the ESC module or coil pack affecting spark timing and/or strength, timing chain stretch or jumping a tooth.

There is quite a bit of testing that would need to be done to narrow it down.