How do you know if you have a bad Coil or Ignition Box????

[Clois Harlan]

After work yesterday I got in my Cobra and tried to fire it up for a little mind de-tuning ride. Starter spun like crazy and I was getting plenty of fuel but it would not fire. Checked coil wire and there was no spark. So I checked all my connections first and found a loose ground wire at my block. Tightened everything up and turned the key on and the beast came to life.

So I got to thinking, (scary huh?) how would I know if my ignition box had gone out or if I just had a bad coil? Is there some kind of test for this or do we just start to replace parts until everything is working again?

Clois

[OZ]

Same thing just happened to me except I was passing a semi at the time it went dead, thought I had ran out of gas !!! pulled off the road and sent my wife hiking for some gas ( somebody had to guard the COBRA) gauge isn't always right !! Wasn't out of gas ( but the wife was when she got back ) Had to call afriend and haul her home ( Cobra not the wife ) We thought the MSD box had gone bad ( no spark either ) Talked to Lane Automotive and they said to try an old coil first to see if that was the problem. Sure enuff the coil had went bad going right down the road. Saved about $160.00 New coil vs. new Msd box. So I'd say keep an old (good ) coil on reserve as this may happen at any time. My ignition system 4 yrs old, first time I have ever had a coil go bad, ever.

[Bud Man]

My MSD coil lunched after a whole 450 miles. Pulling out of a parking lot and then nothing. Dropped in a new Accel, and all was fine.

Thats why Nascar runs two.

Bud

[Clois Harlan]

How did you know it was your coil and not your MSD Box?

[petek]

Testing the coil is pretty easy. Disconnect from the box, attach a ground to one lead on the primary of the coil. Take a jumper from the other lead of the primary on the coil and touch it against the battery positive (briefly). If the coil is good the secondary of the coil will produce a spark.

Testing the full functionality of the box would be tougher ... but a simple test would be to watch your tachometer (as most tachs are attached to the box). If the tach is moving, then the box is sensing the rotation of the engine. Next, monitor the output of the box (across the leads that go to the coil). You should see the output changing (no output to +battery voltage) as the engine turns over.

[OZ]

I had an old one off another car, I knew it was still good so I replaced the one on the Cobra with it to see if the car would start, sure enuff it started right up. The people at the automotive shop suggested that I check the coil first before getting another MSD box to make sure that was what I needed.
Like I said , saved me about $160.00.

[Satanpez]

Its a good idea to set the ignition wiring up so that you can bypass your MSD (or whoever) box. Few years ago my MSD box ate itself while I was out somewhere. Popped the hood and less than a minute later I was ok to drive.

Of course...my MSD coil died also a few months later.

-steve in nj-

[Clois Harlan]

Thanks Pete,

Steve,

My MSD box is located under my hood, is yours? I wonder if all the heat under my hood could cause these components to fail sooner than they are designed to.

Clois

[Bud Man]

Clois:

I don't have a B&B, but I would recommend mounting the box inside the cockpit to the passenger side of the firewall. If it comes with the four rubber shock mounts, use them. If not, I would recommend using a rubber spacer at each end to isolate the box from the surface of the firewall and to help absorb shock.

When my Blaster 2 coil fryed, I was concerned that perhaps the stock mounting (upright, to the front of the drivers side head) was creating an unnecessarily hot environment.

When I called MSD's tech department and asked them if the location and engine bay temp could have cooked the coil, the answer was "No, they just sometimes go out". When I said it only had 450 miles on it, they said "it happens".

Scary.

Bud

[Satanpez]

Clois:

Under the hood. But it was a '65 Falcon 6 cyl. Not the hottest underhood areas.

Replaced it with a Crane HI-6 ignition. (which gave better performance.) Lived through that '65 Falcon, then in the engine compartment of my '65 Mustang, now it's lodged between the battery and inner fender in my '90 Mustang. (almost nowhere for the heat to go) Maybe it's built much better? I never remember either ignition box getting warm to the touch.

Most people install them under the hood. Just don't stick it near the exhaust or radiator.

-steve in nj-

[SCOBRAC]

Replace the coil first it's cheaper. Actually if the coil has power it would be the ignition box, if there is no power to the coil it would be the box (or the ground) (or the switch)(or the battery)

[SCOBRAC]

yes heat and vibration can cause failure..

[SCOBRAC]

BTW, the MSD box is garanteed forever. Send it back they will send you a new one.

[Rick Parker]

Several years ago I was out on an afternoon run in the foothills when I experienced some thing similar. Running down the road at about 3400 RPM the engine just died( equipped with MSD 6)' I immediatly looked at the tach which had dropped to "0". This indicates the primary side of the of the ignition has failed. As it is not sensing the pulses from the distributor and has grounded (shorted out). I waited about 2 hours for Hiway Patrol to come by (no cell phone) and untimately got a tow. First thing I asked them to check was the coil. (Which they determined had failed) Your electronic tach can tell you alot about the primary side of the ignition system.

Rick