I have a 98 Blazer (S10) 4.3 Vortec V6 with 137K miles on it. This engine never has had a problem other than an oxygen sensor going out. One morning I started it, and it was running rough, and then the check engine light came on, steady at first, but goes into blinking when driving. I had the code read, and it came up as P0303 which I was told meant that the #3 cylinder was misfiring. I took it to a mechanic, who did a injector pressure flush for $140.00, and it didn't help. He told me to run it for a few days to see if it would clear, and it still misses after running it for a week.
Could it be the coil pack, or bad fuel injector? The mechanic rules out the on board computer as a problem because only one cylinder isn't firing. I only run fuels with injector cleaners such as Chevron or Shell gas. Also, the mechanic mentioned that there might be a broken line that feeds the injector, but said it would be pouring gas and it didn't seem to be flooding or odor of fuel. Then told me that if it didn't clear after driving, that would be the only option, and cost me $900 more to find out. Help!

 

I would find a new mechanic lol. Did he check the fuel pressure or do a leakdown test? That would help tell you if its an injector problem. I would start by doing a tune up. Definetly plugs and wires. The cap and rotor wouldn't be bad either.