Now issues..

Did you gap the plugs?

 

Might just check to see what the iridiums were set at. Or a mix up in plug wires. DOn't ask me how I know.

 

Are you certain ALL of the extenders have completely snapped onto the plug, especially the more difficult to reach back bank?

Edit: Sometimes it feels like they have but really aren't which may be causing it to run rough unless you did something other than change the plugs. I am aloso assuming the plug wires were put back in the right order. Probably difficult to mess that up given the specific lengths.

 

You said number 1 front bank extender was loose. Was it loose when you removed it?

 

when you test the resistance, make you test from the distribtor terminal to the end of the extender, and wiggle the wire as it enters the cap (to make sure its a solid connection), and also flex the extender and see if the resistance shorts out.

 

You may be able to see a wet plug but you might be getting an intermittent fire from the loose connection. I would try and gently crimp the boot connection.

If the car was running fine prior to your plug change and you didn't do any additional maintenance I cant think of any other obvious reasons why it would be running rough.

 

I have accidentely cracked the insulator on a plug reinstalling it so you could check the plugs themselves for signs of arcing/damage. And believe it or not I have gotten a 'bad' plug before.

 

Also a good possibility...

 

FWIW and not related to the misfire - a "hot" spark plug doesn't produce any more or less spark than a "cold" spark plug. There is no gap setting difference between a hot or cold plug in the same engine. The energy of the ignition system determines how much gap can be reliably jumped at maximum combustion chamber pressure.

Hot and cold as it relates to plugs refers simply to the ability of the plug tip/electrode to transfer heat generated by combustion from the tip/electrode to the cyl head via the spark plug threads. THe idea is to keep the plug at a temp hot enough to burn off deposits but not hot enough to cause damage to the electrodes or cause preignition. Higher combustion chamber pressure/temp require a spark plug that can transfer more heat...a "colder" plug...than one with lower combustion chamber pressure/temp.

 

That's interesting Mike. So if I understand you correctly, a "colder" plug is better for the 308? I'm concluding this since our combustion chambers are high pressure/high temp so we want to maximize heat transfer to the head?

 

Phil, it's not about maximizing heat transfer, it's about an ideal amount of heat transfer. Too little and the plug ends melt, too much and they carbon foul. Ok those ARE the extremes but you get the idea.

If you used the same extenders, which it seems that you did, you may have broken/fractured/stressed one and it is now a bear to find. If nothing else is working, remove plug wires one at a time and see which cylinder is causing the problem.

Lester

 

Jeff,
Check to make sure you did not bump off a vacuum line or sensor wire or....

 

"Phil, it's not about maximizing heat transfer, it's about an ideal amount of heat transfer."

Exactly right. Obviously any plug is a compromise because conditions in the engine vary dramatically from idle to WOT in top gear and a plug has to be able to function satisfactorily under all conditions. That's why GENERALLY when an engine is used for racing/track, it is pretty common to use a slightly colder plug because the combustion temps are much higher under those load conditions than they are for street use.

But if you left the plugs in that you used for racing/track, it would tend to foul in street use because the tip/electrode would transfer heat too effectively to stay hot enough to burn off deposits.

 

Jeff,

Removal of the caps is straightforward. The most difficult part can be sliding off the rubber boot. There is a cork gasket that may need to be replaced after you remove the distributor via the three screws.

The wires in the cap are held in place by small brass screws. If I remember correctly I believe there is a small cap over the wire in the center.

The two coil wires slide off and yes you need to either depress or pull out on the clips. Just go gently and you will figure it out.

Can you take a pic of the shaky looking wire to the extender. If I were you I would see if I could make that connection tight by gently crimping the connection.

I purchased a length of plug wire from Dave and built my wires myself. Not difficult to do.

If you need me to go verify how the coil wires are removed let me know and I will take a trip to the garage.

 

whoa, before you start rebuilding things.....

Before doing anything, I would test the extenders again. I konw you did already, but retest them flexing them a little to see if one shorts out while flexing. Pull the plugs to see if one is fouled/wet, and start with that exender.

if you want to test the whole dizzy cap/wire system then:

pull off the caps, but leave the distributor in place for the time being.

The caps come off with three screws and they only go back on the distributor one way. Once you have the cap off, I would visually inspect it for cracks and worn terminals where the rotor is gouging into the terminal. Also, inspect the rotor for cracks and general wear.

Once the cap is off, test the resistance from the copper terminal inside the cap, all the way to the end of the extender, wiggling the wire gently as it enters the cap to make sure you have good continuity.

If it ran fine before you changed the plugs, chances are
1) you gapped the plugs wrong (double check)
2) an extender is shorted
3) you disturbed a wire/connection somewhere between the distributor and the extender

i would check that before rebuilding anything, my two cents.

Good luck, be patient and have fun.