Weak Firing on #6 Cylinder

[Red Diamond]

Pulled the #6 plug wire and made no difference in the engine rotation at all. Pulled the plug and attached the plug wire, started it up and it's firing alright, but very weak. When the #2 is pulled the idle drops off considerably. I can pat touch all the other header tubes, but the #6 I can hold my hand on it a little longer. Also the #5 wire removed doesn't seem to affect the idle very much either.
Anyone experience this, any help would be appreciated.

'99 Interstate, 32K miles.

[Michvalk]

Sure it's fire? More likely a partially plugged slow jet. Pull the plug, and check color. Should be a light tan or light brown. If it is real dark or sooty, fire problem. At least that is where I would start. Might put a part can of seafoam or some such cleaner in and run that through.

[Red Diamond]

Sure it's fire? More likely a partially plugged slow jet. Pull the plug, and check color. Should be a light tan or light brown. If it is real dark or sooty, fire problem. At least that is where I would start. Might put a part can of seafoam or some such cleaner in and run that through.

Mich, that plug was dark and sooty. I pulled a plug from my Tourer and installed in place of the other plug. The exhaust manifold was super hot as it should be. I also adjusted the pilot screw a little, it is not running like I think it should, so I will install a new set of plugs. Thanks for the reply.

[Disco]

Hi Eli!

If plugs don't make things better and if 5 & 6 are still acting the same, despite the low miles, I might include coil check in your troubleshooting. 

DFG

[ryord]

I would also check the wires, I had a heat related problem with 3 and 4 wires one was bad both sides did not fire.

[Mo Lee]

Sounds like time to rebuild petcock! About a year ago mine started misfiring on #6 plug was fouled I changed plugs and it did the same in a couple of days. Turns out #6 is where the vacumn line runs to the petcock and the diaphrams were allowing fuel to be pulled into the intake thru the line and fouling the plug. As for #5, I don't remember how the cylinders is layed out but if it is the right rear cyl directly across from #6 it can seem weak due the fact when you pull that wire it actually balances the engine out a little because of #6 not firing.

[Michvalk]

Sounds like time to rebuild petcock! About a year ago mine started misfiring on #6 plug was fouled I changed plugs and it did the same in a couple of days. Turns out #6 is where the vacumn line runs to the petcock and the diaphrams were allowing fuel to be pulled into the intake thru the line and fouling the plug. As for #5, I don't remember how the cylinders is layed out but if it is the right rear cyl directly across from #6 it can seem weak due the fact when you pull that wire it actually balances the engine out a little because of #6 not firing.

Good Catch!!

[Valk55]

Sounds like time to rebuild petcock! About a year ago mine started misfiring on #6 plug was fouled I changed plugs and it did the same in a couple of days. Turns out #6 is where the vacumn line runs to the petcock and the diaphrams were allowing fuel to be pulled into the intake thru the line and fouling the plug. As for #5, I don't remember how the cylinders is layed out but if it is the right rear cyl directly across from #6 it can seem weak due the fact when you pull that wire it actually balances the engine out a little because of #6 not firing.

+1 to that. I just experienced the same problem. Re-built the petcock and problem solved. 

[Ricky-D]

How well the carburetors are synchronized can be a large contributor to what you experience.

***

[Red Diamond]

Thanks for all the responses, I'll be getting on all the mentioned issues later today.

Dave, the #5 & 6 coil was certainly one of the things I thought might be a problem because the spark was very weak. When the plug wire is removed from the #5 plug, you can actually hear the spark jump, no such thing on the #6 plug. When any other wire is removed, there is a marked affect on the idle.

[R J]

Run a new wire temporarily to #6 and see if it fires better.  If it does, you have a break in the current wire somewhere.

Usually happens when ya grab the wire and jerk on it,  It will break the carbon inside the wire.

My grandson did that on MGM.

[BonS]

The spark plug wires are copper not carbon. Yes, copper can break but it's relatively rare. There is a carbon resistor in the spark plug boot on the plug and these do go bad, on occasion, and can cause a weak or no-fire situation.

[Ricky-D]

The spark plug wires are copper not carbon. Yes, copper can break but it's relatively rare. There is a carbon resistor in the spark plug boot on the plug and these do go bad, on occasion, and can cause a weak or no-fire situation.

You should be cautious when changing out the different components of the ignition system without doing due diligence regarding the compliance of components in a cd ignition system.

There are many more considerations besides just the ability to make a "spark".

That all aside, I would suggest to perform a compression test to insure the motor is in proper condition.

***

[sugerbear]

The spark plug wires are copper not carbon. Yes, copper can break but it's relatively rare. There is a carbon resistor in the spark plug boot on the plug and these do go bad, on occasion, and can cause a weak or no-fire situation.

and can be broken by yanking on them.