[FC] Coil problem

[Dale Dewald]

Hello Ben,

At 18:43 7/5/07 -0400, Ben's Bus wrote:
>Well folks, after the van died on the way home the other night and I got 
>it towed to the garage, things have gotten more interesting.
>
>I noticed that evening that the yellow wire going from the coil to the 
>ignition switch connection in the engine compartment had melted plastic 
>sheathing. Too much juice somehow, I guess.

The ignition coil circuit carries about 3-4 amps of current during normal 
operation.  This is the peak current while the coil is charging so the 
average current will be somewhat less.  This is not enough to melt the 
insulation on the 20 gauge coil wire.

>The guy at the garage called today and told me it was ready. He replaced 
>the melted wire; said it was not heavy enough for the load and it finally 
>quit. I went to get the van.

Who is this guy at the garage? Is he a certified mechanic? See above. Did 
he not consider WHY the stock wire would have suddenly melted? Obviously 
there was a short or some other malfunction that made the wire carry too 
much current.  Installing a bigger wire is like replacing a blown 5 A fuse 
in a light duty circuit with a 30 A one and hoping the problem goes away.

>  Started fine, ran fine, then, four houses from home I heard the same 
> "bang" in the engine compartment as Tuesday night and the engine died. I 
> coasted into my driveway and got out to investigate. The HEAVY 
> replacement wire from the coil was intact and not melted. I fished around 
> the wiring for a few seconds. Five minutes later, the van started right 
> up and I drove it back to the garage.

This sounds like a failing coil that is shorting to ground.  The "bang" was 
probably an explosion of raw gasoline vapor that accumulated in the exhaust 
system when the coil suddenly quit, yet the engine kept turning for a 
moment, pumping unburned mixture through the system.

>He says he will check the coil and make sure nothing is wrong with it.

This is what he should have done in the first place.  Check with an 
ohmmeter in every conceivable manner and then check current with an 8 volt 
source. It may be okay on the bench but only shorts out when it warms 
up.  I would swap in a known good coil and drive for a while.

>  Any idea what is going on here? I have driven several thousand miles on 
> this engine and its components without a glitch until Tuesday evening.

It sounds like a bad coil to me. BTDT

>What would make a "bang" sound and shut off the engine...then allow me to 
>start it five minutes later? I am sure it is part fo the ignition system...

See above.  I once had a new (2 months old) coil fail when warm but work 
fine when cold.

Dale