DeTomaso Mailing List: February 1997, Message #151
     



From: MikeLDrew@aol.com

Subject: Plug Wars

Date: Tue, 25 Feb 1997 09:02:22 -0500 (EST)



This came off the Nor-Cal Shelby net, where folks have spent the past few

days discussing the virtues of various brands of spark plugs and wires...





A few comments about plug wires.



1)-They DO wear out. Usually insulator leakage. Once in awhile the "wire"

opens up (carbon filled wires do this). I will NEVER have a carbon filled

wire on any vehicle I ever own for the whole rest of my life. Junk.



2)-Sometimes people inadvertantly wear their ignition wires out a lot

faster than necessary. You can accelerate this "wearout" by "checking

the spark" by pulling off a plug wire and waving it around in the air.

With a good ignition, those electrons WILL go somewhere, and that somewhere

is:



-through the plug wire insultion. Once done, it's like a hole poked in

it, it will leak through that hole from then on.

-Carbon track the inside of your distributor cap.

-Carbon track the outside of your distributor cap.

-Carbon track the outside of your coil tower (the part the distributor

wire plugs in to).

-Wipe out your coil. (Right away with a composite filled "yello top" or

slow death with an oil filled coil).

-Wipe out your CD amplifier

-Late models ... wipe out the ignition amplifier.



If you MUST check a spark plug by pulling the plug wire off, stop the

engine, pull the wire off, place it back over the plug gently, start the

engine, and don't pull the insulator away from the external plug tip (this

distance requires over 20KV to achieve!). Better yet, have a conductive

spacer to put inside the plug wire of interest. Voltage required to jump

an air gap is ~20KV per CENTIMETER. So, an inch is 50KV ... which is well

beyond the insulative capability of vintage plug wires and is about what

new ones will stand. Go beyond this and you break something (down) that

you can't see!



You can also achieve most of the above mischief by removing the distributor

cap and cranking the engine over.



The safe thing to do for your equipment:  DO NOT OPERATE OR CRANK THE

ENGINE WITH ONLY SOME PART OF THE HIGH TENSION SYSTEM DISCONNECTED. PERIOD.

END OF STATEMENT. DO NOT ARGUE. DO NOT NATTER. DON'T DO IT.

If you need to crank the engine with the high tension circuit disconnected

you can do one of two things to disable the system (the source of sparks

and mischief)

-1)-Disconnect 12 volts to the coil primary (the PLUS terminal).

-2)-Disconnect the distributor to the coil primary (the MINUS terminal).

-3)-Disconnect the high tension lead from the distributor and GROUND it

(thus "shorting out" the coil (shorting out is good in this case) and

protecting it from itself.

-4)-On late models, there may be a connector on the ignition amplifier

that can be disconnected.



I have rarely read literature that is clear on this. I have often read

literature that tells you the wrong thing. If any of you remember the

old "Fixing your VW for the Compleat Idiot" (a GREAT maintenance book

except for ignition), the author would tell you to pull the plug wire

to protect yourself or to keep it from starting while cranking over the

engine. Then he bitched about how bad Bosch ignition coils were! Dumb.

Really dumb. He never did figure that one out.



Oh, by the way. An oil filled coil should NOT be installed with the high

voltage tower pointing up. That's cuz there has to be some air in with

the oil to allow for oil expansion as the coil heats up. If there isn't

enough air in the oil cavity, the oil will expand, creating a leak and

it will run out of the coil; when the coil cools off, air will go inside

to displace the lost oil ... so ya can't win this one. If the air is between

the high tension lead and the low tension leads, the spark can arc inside

the coil and slowly destoy it. Not to mention lousy peak ignition voltage

while it's doing this. Yeah, I know, it's real convenient to mount the

coil tower up. If you must do this, get a composite filled coil (like

the old vintage Ford yellow tops ... a very good coil by the way ... as

long as you don't break it as above). My favorite vintage "killer" coil

is the Mallory Voltmaster (the big square black thing); best coil I ever

measured and characterized ...  (but don't mount it tower up!). Also a

GREAT coil for CD ignitons.



An engine compartment is a hostile place for ignition wires, they do wear

out. But, they should last at least 3 years with normal street use.



It was interesting to hear which brands have achieved the ire of their

owners.



Don Wollesen

Former Ignition Wonk