MSD Diagnostics

[Kevin G.]

Ok - I've replaced the burned out rotor - nope, the easy fix didn't work.

I removed, cleaned and replaced the dizzy. Still no joy. I even found a few bare spots on the wires from the optical reader in the dizzy to the crane optical trigger and fixed those.

I've still got the nasty miss between 3-4K rpm.

Now I'm going to look at the MSD unit for the problem, but can't find anything on testing the unit for erratic behavior.

Does anyone know of any tests I can run on a MSD 6AL unit to see if it is the problem? I surely don't want to spend the bux for a new one if I don't have to.

Thanks,

[JSDSKI]

Do you have the right coil for the MSD? It's the Hi Vibration or something like that. Check on Steve W rennsport.com. Did you test each plug wire (or do you have Magnecor's?). Ground straps are ok? Dist advances correctly?

Awhile back, one thread said that cleaing the main engine harness connector with electrical contact spray cured a variable miss problem.

[Kevin G.]

Scott -

I am using a Bosch Blue coil with the MSD, seems to be working fine. I also have the Magnecore wires, all of which were installed together during the ingition upgrade.

The distributor appears to be advancing correctly, 2 deg BTDC at 900, advancing to 30 ATDC at 6K, although my timing light is challenged at 6K. Maybe someone can invent an ultraviolet timing light with UV paint on the marks so we can actually see them at high rpm. All I get is a faint ghost even with a blanket to block out sunlight.

I have not plotted an advance curve, so maybe I'll try that out next. Does anyone have the 'approved' advance curve for a Bosch distributor, mechanical advance for a 2.2S?

I checked the MSD sight for troubleshooting, and it appears that as long as you are getting a spark, the unit is supposedly working fine. If anyone has contradictory information, I would appreciate hearing it.

Thanks, all!

[jeff m]

Kevin
To test MSD.
If you search "speed switch" you will find a diagram of a tester that you can make for $10 that will test a MSD or a speed switch that was posted by Warren.

If you combine my user name with that search it will get you there quicker.

Also see if you can borrow a black coil, the one with the lightning bolt on the side and try that.

Also check you beru connecters, mine are 2.9K ohms, I think some are 4K ohms, they should all be within a couple of hundred ohms.

I think they are more likely to become intermittant open but if one were to be low I think that could fry a rotor.

Jeff
911T

[ssoar]

Often electronics will be ok but fail when heated or vibrated.

the msd in my racecar failed in much the same way you describe, except it was a high rpm miss. Static bench testing never revealed a problem

What I did to prove it was the msd was to heat the msd and coil in the oven at less than 200 degress for a half hour, or so.

Then I bench tested it hot while tapping on the side with a block of wood. It then started cutting out.

Replaced it with the Crane unit (I forget the model number) which was a much better unit.

[Elombard]

I have this MSD owners manual and the only test it mentions is done with the car not running. Sort of indicates it either works or not. Did this test show up at the web site?

[Kevin G.]

Elombard

The test on the site consisted of disconnecting the coil wire from the dizzy and positioning it 1/2 inch from an engine ground, disconnecting the white wire from the MSD unit, turning the ignition to the on position, and grounding the white wire repeatedly. This should cause the coil wire to spark.

My problem is not lack of spark all the time, just between 3K and 4K.

I went into a performance shop over lunch, and talked with an old hat who has been selling MSD's for years to the track guys. He said he can only remember a few units that went bad, and those were traced to excessive heat, not vibration. The symptoms were similar though, certain circuits that went bad and didn't totally knock out the unit.

[A Quiet Boom]

I hate to say it but this is where MSD units typically fail, I've got a few well over 10 years old with no problems and I've also had several fail just like this. Typically it's vibration that does it since of the 3 I've had fail all where in high vibration situations. 3k rpm is the crossover point of the MSD unit from multiple spark to single spark, I have yet to see a test for this type of failure though. After the unit exhibits this behavior it will rapidly go downhill until it has only intermittent spark at idle, if it will even achieve idle. Having trusted MSD for many years for all my ignition needs (I've had in excess of 16 boxes over the years) this problem is my one single beef with them. If MSD only had a test method to be sure it was the box I wouldn't complain but to my knowledge they don't. Try a different coil and if that doesn't work I'd say the unit is definately bad.

[Kevin G.]

Thanks, Christian

I plan on swapping to the old black coil tonight to see if that changes anything. I'm pretty sure that you are correct though.

[jabb]

What are the plugs gapped at if 2 big a gap you can get a miss.
try gaping at 42-45.000

[Matt Smith]

Hi Kevin. Sorry, but I havn't been following this thread or your problems, though I must point out that a miss between 3 & 4k could easily be a mixture problem. Was with me anyway, and took forever to cure. Is your MFI correlation spot on? Lean mixture the transition range will cause an annoying, ignition type miss. It's easy as heck to check: just richen the main mixture a click or two, write down exactly what you have done, then road test. If miss has gone, investigate MFI settings thoroughly, follow the blue book and set it up right (because just richeningg it is not really enough. You'll need to get each stack working properly etc..

If it hasn't gone, undo what you have just done (you know this because of your handy notes) and start checking the MSD.

I've got an MSD box too, and I sure know what I'd prefer to do first.

[Steve W]

I had a MSD 6A unit mated with a MSD Blaster coil on my SAAB Turbo and it eventually went bad. When it went bad it progressively got worse and worse until it wouldn't fire under boost. So yes, even if it works while driving, it can already be on its way six feet under.

[Kevin G.]

Thanks, Matt

Earlier on in the problem on a different thread I explained that this was a sudden change from a formerly fine running car.

Because of the suddenness, I don't feel it is a mixture problem, but it certainly doesn't hurt to check!