Cylinder Missing, No Heat

99 Blazer 4.3 4wd

The problem started with no heat. Engine warming up fine, not overheating. I get some heat with the vehicle sitting, idling for 15-20 minutes, but when driving....just cold air. It's a problem that's been getting worse over the past few months. I replaced the t-stat twice, flushed out the old Dex-cool and replaced with regular coolant. In the process of flushing, replacing the t-stat...somehow the engine is running poorly, missing a cylinder it feels like. All vacuum hoses and wiring harnesses are reconnected. Wondering about ignition coil that could've gotten bumped or broke...possibly plug wire?

I need help. Before bringing it into the shop, I want to exhaust my mechanical capibilities. Any way I could flush the heater core without removing it? Can the lines going in be accessed along the firewall? I've also heard about heater control valve issues. Is this accessible?

Thanks in advance.

I also did'nt have heat in my 98 Blazer till I blew out the heater core with a air compressor. I went thru the flushing of the motor twice and no heat. As soon as I blew out the core, I had heat. That was over two months ago and I still have heat. I got the ideal from Blazerguy's posting "Heater core clogging" posted on 1-23-2003. As far as the missing cylinder I have no clue.

I did exactly that last night. Disconnected both heater hoses, ran water through both ends. I couldn't believe the crud that came out. After flushing through and replacing with green coolant, the stuff that came out was red/rusty. So, I flushed the entire system again. I now have HEAT! I intend to give it a month and check it out again, possibly do one last flush to make sure it's purified.

Guess I have sort of the same problem. I'll run water thru the hoses tomorrow to back flush the heater core to see if it helps. The thing is though, I have plenty of heat when the temp dial is all the way to the right on the red square. When I have it on 80 or 76 or 74 or anywhere else, the heat is very weak. Maybe I just have a bad temp dial - I suppose the dial is a thermostat of some sort. Any ideal what is going on?

Its a 98 Blazer 4WD with the auto temperature controls.

As far as your running rough, change plugs and wires if you haven't... it helped mine.