Bad Coil
 

My 71 with a 350 crate has been pis*y about starting the last month or so. Changed the plugs, leaned out the Holley, made sure the choke was working- all the usual suspects.

Sometimes it would just get a bug in its bonnet and decide not to start. I'd fiddle with wires, check stuff, and go through the motions and it would start up. I just figured it wanted attention.

On Monday, after a 1-2 mile drive from work, I parked it in my garage. A moment later I needed to move the truck, and it wouldn;t fire. Quickly figured out there was no spark.

Thinking my HEI wasn't getting enough juice, I cleaned up my circuit by wiring directly into the fuse box- that didn;t help.

I decided I would put in the correct plugs for my Vortec heads (my bad- I ordered plugs without thinking I didn;t have stock '71 heads) Those non Vortec plugs were a sooty mess after only about 75 miles. Obviosuly that didn;t help. In the midst of getting that &^%& #3 plug out from behind my header, I dropped a sizable piece of road crud into my eye. No manner of flushing, rinsing or cussing would work it loose. it took a trip to the minor emergency clinic to get it out... and a tetenus shot. Maybe I should think about taking those safety glasses out of my tool chest next time...

Pulled the cap on my MSD dizzy. It was a mess. Contacts were very pitted. I pulled the coil and checked the coil. I *think* the ohm meter gauge was telling me the coil was "open"- but I'm not really sure. My manual was kind of vague on the subject. I think the PO put a stock coil with the MSD module.

So- I hung a new coil/cap/rotor on, turned the key and it fired instant.

My question- do coils really ever go bad? I've never had to replace one on the kazillion internal combustion engines I have owned. My understanding is that they are rock-simple. What could go wrong? I read a thread and someone stated an MSD module could fry a stock coil, but they didn't elaborate. Have ya'll heard anything like this? These are the things that I think may have contributed:

Accel plugs with a too-short reach for vortec heads
a seriously pitted dizzy cap (motor has few miles)
msd module with a stock coil


What do ya'll think. Did the coil really fix it or was it more a matter of just giving "Bess" undivided attention for a couple of hours that made her spark? (I haven't washed her in a week or so)

Thanks Folks

Re: Bad Coil
 

Yes they can go bad, I've had a couple that did. It's an electrical component, life expectancy is from 10 sec to 50 years. Thats why there is no returns on electric components.

Re: Bad Coil
 

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I had a coil go bad on a '47 Chevy truck I owned once. Driving down the road and it was like you just turned the key off....:o

LockDoc

Re: Bad Coil
 

Having that happen sure sends you on a long search to narrow it down.

Re: Bad Coil
 

Well- I spoke too soon. Just went to start the truck and it just spun. No fire. I'm okay getting juice to the HEI. I have 12.4 volts to the connector. Before I start thinking about a bad MSD ignition module, is there a smarter solution? Do I have a ground problem on my truck?

I think all of my straps are intact- 2 straps engine to cab, 1 strap cab to chassis. How should i be grounding my engine to frame?

Re: Bad Coil
 

CCD3
Its seems that you have an intermittent module or trigger in your distributor.
A.P.

Re: Bad Coil
 

i read that your wired to the fuse box did u use the yellow wire oringaly? if so the yellow wire only delivers 9 volts and and will burn an hei coil up

Re: Bad Coil
 

I'm leaning towards thinking it is my module.. it was my original hunch. I 'm not using the yellow wire. I bit the bullet and installed an MH engine harness for HEI and did away with it.

here's what I don't get- when it runs, it runs perfect... not a miss from idle to WOT. I thought maybe a faulty module would give a little degradation in performance or at least give me a warning hic-up or something.

Does anyone know how to put a meter on the module? I'd rather check it than hang a part.. I already bought a coil I don't think I really needed.

My next step is to make absolutely sure it's not a ground-issue. I'll strap the engine to the chassis really good and check. If that doesn't work, I'll alligator clip a ground from the ground clip on the distributor and put it to the frame to check.

If ground checks out, I guess I'll an el cheapo module from O'Reily for testing. They have a $17 job that will work as a tester. I just don;t want to shell out $90 for an MSD module if it is something else. All this makes me wish I was a mechanic, and not a parts-hanger.:confused:

Re: Bad Coil
 

CCD3
I few years a go I was having problems with my car's distributor. I checked the coil and that was O.k. then I removed the module and took it to autozone. They tested it and it passed. Thats when the guy told me that the trigger in the distributor was bad. I ended up replacing the entire distributor. Take your module to your local auto parts and see it they can test it.

A.P.

Re: Bad Coil
 

Thanks for the info. When I asked my Autozone if they could test my ignition module they just stared at me... I htink maybe the manager drooled a little.

I found the test spec on the MSD ignition page for the module- there should be between 400-1300 ohms between the pickups. When i get a chance- I'll pull the innards out of the distributor and give it a try. Probably have to wait until next weekend- My 3 yo is having a b-day party today. Wife gae me "the look' when i said "I just want to try one thing..."

Thanks for your help