Wierd misfiring

I have a 1999 chevy lumina 3.1 with only 317,000 mi. and running strong.I had put new plugs,and wires about 6 weeks ago. The other day it started misfiring and I could smell the gasoline. I checked the tail pipe and it showed black smoke. In addition I put a piece of paper on the tail pipe and I could feel the misfiring with a consistant rythm. I notice that it is running flooded(like if a fuel injector is not working correctly.) I cleaned the throttle body, checked all the coils and the spark plugs and they are good. It does not show any check engine light on. What could it be?

Not sure how to determine a spark plug is good? by looks? I'd pull one plug wire at a time to decide which cyclinder is misfiring- then swap wires, plugs, and coils to decide which one the trouble follows. A GM tech II scan tool will indicate the misfires- by counting them and tell you which cylinder.

Only 317K miles?

New plugs and wires.....use OEM plugs?

Do you "feel" this more at idle, or when under a load like, up a hill?

Double check the wires that they are properly attached? And that they have not been misrouted and grounded on an exhaust manifold...

When you have a misfire, the O2 sensor does not sense fuel in the exhaust, it senses unburned oxygen....so because of the misfire, and the presence of oxygen, the O2 sensor sees a "lean" condition, and commands the injectors rich, which further compounds the situation.....

Maybe plugs and wires are ok....may have to check coil output with a spark tester........

Not sure how to determine a spark plug is good? by looks? I'd pull one plug wire at a time to decide which cyclinder is misfiring- then swap wires, plugs, and coils to decide which one the trouble follows. A GM tech II scan tool will indicate the misfires- by counting them and tell you which cylinder.

Thank you for trying to help me. I verified plugs are good ( cheking continuity amd ohms).changed coils and wires. Also switch them. I noticed one cylinder that was wet. So I changed the plug and coil and ran the enigine for about an hour. I found that the cylinder was wet again(gasoline) and the plug that I switched to another cylinder got cleaned. I am not getting any check engine lite on. I know that the lite is working. I think that it might be an injector. What do you think?

Only 317K miles?

New plugs and wires.....use OEM plugs?

Do you "feel" this more at idle, or when under a load like, up a hill?

Double check the wires that they are properly attached? And that they have not been misrouted and grounded on an exhaust manifold...

When you have a misfire, the O2 sensor does not sense fuel in the exhaust, it senses unburned oxygen....so because of the misfire, and the presence of oxygen, the O2 sensor sees a "lean" condition, and commands the injectors rich, which further compounds the situation.....

Maybe plugs and wires are ok....may have to check coil output with a spark tester........


Thank you for trying to help me. I verified plugs are good ( cheking continuity amd ohms).changed coils and wires. Also switch them. I noticed one cylinder that was wet. So I changed the plug and coil and ran the enigine for about an hour. I found that the cylinder was wet again(gasoline) and the plug that I switched to another cylinder got cleaned. I am not getting any check engine lite on. I know that the lite is working. I think that it might be an injector. What do you think?

That's not really how to check a plug.....one way is to swap them like you did.....

Apparently you have replaced coils and wires......What number cylinder is wet(could it be number one, back side of engine, first one on the passenger side)? What you want to does is attach a Spark Tester to the end of the #1 wire and check for spark....if it's not #1 that is wet, attach it to whatever cylinder was wet....do you get a healthy spark when cranking? If yes, then I would pull the plug and check the compression in that cylinder......

Have you been losing coolant? Reason why I guessed #1 cylinder, if you are going to have a head gasket problem, that is the most likely cylinder it happens in.....just from experience....

Compression is 150 lbs ( same as all the rest) problem is with cyl. #4. How can I check the fuel injector and the harness? Should I take out the plenum? I really appreciate your help. Thanks