Help me figure out this misfire

[76k5blazerr]

My 76 blazer with a 350 started misfiring out of the blue last night, it's cylinder 3 I'm pretty sure cause I pulled the wire off and it didn't change the way the motor ran. I just replaced all 8 plugs this morning and the cylinder three misfire is still there, also the plug wire pops and arcs fine when you hold it near the plug, so i think the wire is fine. Who's got some ideas? I want to get this straightened out. Thanks guys

 

[76k5blazerr]

Update: I just pulled the plug out of cylinder 3 and stuck my finger over the hole and cranked the motor over and it does have compression, still missing. Anybody have any ideas?

 

[rampage]

Have you looked at the condition of the cap/rotor?

 

[76k5blazerr]

Haven't checked that... What do I look for?

 

[rampage]

Corrosion, worn/loose contacts or carbon buildup. Basically, anything out of the ordinary.

 

[76k5blazerr]

Ok, anything else that could be causing this? Also, will it hurt the motor any to drive with the misfire? I kinda have no choice, it's my daily driver.

 

[rampage]

Best to check the simple, cheapest and most likely cause of things first. If you have a catalytic converter it will wear it out faster due to the unburned gas and it'll also hurt your wallet.

 

[rampage]

And the unburdened gas could mix with the oil which wouldn't be good for the motor, so I'd recommend an oil change also.

 

[76k5blazerr]

Well I'm driving the truck right now and the misfire just randomly quit when I stopped at the gas station for a drink. Went back outside cranked it up and it's running like normal. What the hell?

 

[diesel4me]

Define "Misfire"..

Was it just running on 7 cylinders,like one was "dead"--or was it skipping intermittently ,or popping back through the carb or exhaust?..

If it was running on 7 cylinders like it had a dead cylinder,it might have had a piece of carbon in the spark plug electrodes that shorted that plug out,and it came out by itself..or it might have a carbon track in the distributor cap (that is not always visible to the naked eye),that allowed the spark to jump to ground there,instead of firing the spark plug..
That can cause intermittent "skipping" as well..it happens often when it was damp or rainy out,then if the weather dries up it'll usually stop ..a bad plug wire can do this too--see that none have rubbed thru on something,or got burned on the exhaust manifold..

 

[76k5blazerr]

It was a dead cylinder. I am going to replace the plug wires in the next couple days just to be sure it don't happen again, spark plugs are brand new as well.