Ignition Problems

[mark grady]

I'd guess that the coil passes the resistance test, but is breaking down
internally.

That failure path lead to poor spark/performance, which finally resulted in
the total failure of the high voltage side of the coil.

Back in the hey days of the HEI, we used to use the AM radio in the vehicle
to 'listen' for a coil failure. You could easily 'hear' the internal HV
short every time a plug fired.

Mark Grady

PS: With all these coaches in MB, we're almost all alone, eh?

> -----Original Message-----
> From: owner-gmcmotorhome
> [mailtowner-gmcmotorhome]On Behalf Of
> EMERYSTORA
> Sent: Monday, March 22, 1999 1:17 PM
> To: gmcmotorhome
> Subject: GMC: Ignition Problems
>
>
> We were in a campground in Tucson, AZ and I started the engine
> after sitting
> for three days. It ran for about 60 seconds and then wouldn't start. At
> first I thought it was flooded but, when pulling a spark plug, I
> had such a
> weak yellow spark that I concluded it was the ignition system. I
> replaced the
> cap and rotor (both only about 3 months old) but that wasn't the
> problem. I
> tested the coil with an ohm meter according to the instructions
> in the service
> manual (by the way they have the two steps reversed in the picture). This
> told me the coil was OK. I next purchased a module. This still
> didn't solve
> the problem. I pulled the distributor and replaced the pickup
> coil. Still no
> good. By now I'd replaced everything but the coil so I went to
> the A/P store
> a fourth time and bought one. Hooray, it worked!!
>
> Even though the coil passed the test detailed in the manual it
> was faulty. My
> engine performance was better with the new coil so it apparently was not
> giving good spark for some time and finally gave up the ghost. At least I
> have a backup set of cap, rotor, module and pickup coil.
>
> Moral of the story: Don't always trust the part even if the GMC
> manual says
> it passes the test!
>
> Emery Stora
> 77 Kingsley
> Santa Fe, NM
>

 

[jim bounds1]

Emery,
Funny that happened to you, the same thing happened to me with no warning 1
1/2 miles from home coming in from the Myrtle Beach rally. I did exactly
the same diagnosis that you did. I ended up replacing everything in the
Dist. even though I felt the yellow spark meant a weak coil. Before I
found the yellow spark I had felt that the pickup wires had shorted since
they do rest on the moving vacuum advance arm and are suseptable to
chaffing. I feel better knowing all the electrical stuff in the dist. is
new. Yes, it is a good idea to carry a module and pickup in the coach. I
would also add a coil to your spares list- you never know and that stuff
packs up pretty small!

See ya,

Jim Bounds
- -----------------------------

>We were in a campground in Tucson, AZ and I started the engine after sitting
>for three days. It ran for about 60 seconds and then wouldn't start. At
>first I thought it was flooded but, when pulling a spark plug, I had such a
>weak yellow spark that I concluded it was the ignition system. I replaced
the
>cap and rotor (both only about 3 months old) but that wasn't the problem. I
>tested the coil with an ohm meter according to the instructions in the
service
>manual (by the way they have the two steps reversed in the picture). This
>told me the coil was OK. I next purchased a module. This still didn't solve
>the problem. I pulled the distributor and replaced the pickup coil.
Still no
>good. By now I'd replaced everything but the coil so I went to the A/P store
>a fourth time and bought one. Hooray, it worked!!
>
>Even though the coil passed the test detailed in the manual it was faulty.
My
>engine performance was better with the new coil so it apparently was not
>giving good spark for some time and finally gave up the ghost. At least I
>have a backup set of cap, rotor, module and pickup coil.
>
>Moral of the story: Don't always trust the part even if the GMC manual says
>it passes the test!
>
>Emery Stora
>77 Kingsley
>Santa Fe, NM
>
>
Jim Bounds / Co-op Motor Works Orlando www.gmccoop.com