Engine misfire? - multiple cylinders not firing?

[wonl2]

Hello Forum members I have an interesting problem that I hope isn't serious. I have a 1979 L48 with just over 60k miles. When I bought the car, about 500 miles ago, the car would spit carbon out the exhaust pipes at initial start up. I changed the plugs to the correct heat range, AC Delco R45TS and everything was great. I recently went to start the car and go for a spin but the car was running really rough and would stall on me. It seemed as though the engine was flooded because I would have to keep the pedal to the floor in order to keep the engine running to limp it back inside the garage. I opened up the hood and was moving the spark plug wires thinking they may be loose and noticed something really strange. The #3, 4, 6 and 7 cylinder headers were hot but the rest were slightly warm at best. Any ideas on what's wrong? Hopefully I just need a tune-up.


Any and all comments and suggestions are greatly appreciated. Thanks in advance for your replies.


Phil

 

[Malcolm foy]

Did you replace wires and cap when you changed plugs? Or just the plugs if not I would start there, A bad dist cap can cause all of the problems you have mentioned. Also sounds like you have some bad wires

 

[wonl2]

I just replaced the plugs.

 

[Peer81]

I would say to much fuel!
To much fuel will give you carbon exhaust output, will wet the sparkplug so they don't fire. And you need to floor the pedal so get maximum air in the engine to mix the the (to much) fuel just to keep it running. But if this is the case you should smell the fuel and it should burn your eyes.

Greetings Peter

 

[Hib Halverson]

I'm going to guess the problem is not fuel.

Four hot pipes and four warm ones means you've got 4 cylinders misfiring. If you've got four misses that explains why the engine is running so rough and why you have to keep so much throttle opening to keep the engine running.

I'd look for the cause of the misfire first.

Pull out those plugs and see what the misfiring ones look like. Inspect, and test if possible, your plug wires. Take a look at the cap and rotor.

 

[tnovot]

What did you mean when you said that "everything was great" after you changed the plugs to the correct heat range? Did the engine run fine without a miss until some later time? Aside from the carbon spitting out upon startup, did the engine run without a miss or did it run rough immediately following the plug change? If the problem began right after the plug change, I'd check to make sure you did not get two pairs of plug wires crossed.
When you get it figured out, don't forget to let us know the solution.
Terry

 

[wonl2]

The engine ran normally after the spark plug replacement. I have noticed that the car had no acceleration when entering the highway from the on ramp. The car did sit a while in the previous owners garage. I was planning on rebuilding the quadrajet anyway due to the length of time the car was sitting. She needs a little TLC.