MSD Issues

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74 Slant Six

74 Slant Six

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This is the 3rd MSD unit that has failed in the last week. My car is a 74 Plymouth Duster with a Slant Six. Motor is new and engine bay has been completly redone. On all grounds are on bare metal. Car starts and runs great for a while then starts to run rough then dies and won't restart. All other electronics are in perfect working order.
1. The 2 main heavy gauge wires are run directly to the battery.
2. The smaller red wire is run to the solid brown wire from the harness that has 12volts in the run posistion. Is this my error should it be 12volts to start then less voltage to run?
3. The 2 trigger wires are run to the distrubutor.
4. The two coil wires go directly to the coil.

All connections have been soldered and heat srunk. The ballast resistor and wires have been removed along with the electronic box and wires.
Did I make a mistake be removing these? The other thing on the trigger wires running to the distrubutor I ran from the top of the firewall down over the plug wires. Thinking this was the problem on the 3rd unit on the trigger wires I ran across the firewall and down around the overflow bottle so there is no interference. Sorry to be so long winded but I know you like as much info has possible when helping people out.

Thanks,

Bill
 
74 Slant Six said:
This is the 3rd MSD unit that has failed in the last week. My car is a 74 Plymouth Duster with a Slant Six. Motor is new and engine bay has been completly redone. On all grounds are on bare metal. Car starts and runs great for a while then starts to run rough then dies and won't restart. All other electronics are in perfect working order.
1. The 2 main heavy gauge wires are run directly to the battery.
2. The smaller red wire is run to the solid brown wire from the harness that has 12volts in the run posistion. Is this my error should it be 12volts to start then less voltage to run?
3. The 2 trigger wires are run to the distrubutor.
4. The two coil wires go directly to the coil.

All connections have been soldered and heat srunk. The ballast resistor and wires have been removed along with the electronic box and wires.
Did I make a mistake be removing these? The other thing on the trigger wires running to the distrubutor I ran from the top of the firewall down over the plug wires. Thinking this was the problem on the 3rd unit on the trigger wires I ran across the firewall and down around the overflow bottle so there is no interference. Sorry to be so long winded but I know you like as much info has possible when helping people out.

Thanks,

Bill
Click to expand...
Info....which MSD box are you using?
 
I have the MSD 6AL in both my cars and have no problems with either one.It sounds like your hooking them up properly,is your battery old or new fully charged?For 3 in a row to go,somethings not right.
 
Could they be getting water in the box? The box looks water-tight, but it isn't.
 
Sure it isn't the pick up in the dist. ? Sounds hooked up right. Something isn't right if ya went through three boxes.
 
I've been running msd systems for 5+ years now not one failure to speak of,not saying their perfect but 3 in a week sounds like something else is at fault or affecting the boxes..
 
Here is the diagram (top). Looks super easy setup. Agree something is definitely wrong if you went through three. I'm using a 6AL with no issues either.
 
I have done the wiring per the MSD instructions. I just picked up the new box. I'm removing all of the old wiring from the previous MSD unit and starting over. I will check in later with the progress.

Bill
 
You haven't been mig/tig or arc welding on the car with the box hooked up, have you?

Keep us updated.
 
I just replaced my 6A about a year ago. Prior to that it had been in service since 1985. I just installed a Mallory system with a rev limiter. I tend to think that you may have a week pickup or reluctor in the distributor. I can see the pickup opening up after the under the hood temps get high enough. If you have access to a different distributor try putting it in.

Good Luck
 
superchargeddrt said:
I just replaced my 6A about a year ago. Prior to that it had been in service since 1985. I just installed a Mallory system with a rev limiter. I tend to think that you may have a week pickup or reluctor in the distributor. I can see the pickup opening up after the under the hood temps get high enough. If you have access to a different distributor try putting it in.

Good Luck
Click to expand...

You got me thinking? Prior to changing the engine I put the first unit on with no issues. So what changed other than the engine? All the wiring was the same as is the distributor and coil. Well I changed the distributor cap and rotor. I just took the distributor out and the reluctor looks quite black. So I put the rotor and cap on and spun the distrubtor in my hand and no clicking sound? Put on the old cap and rotor and it makes the clicking sound! This might be the issue, I'm running all the wires and will retry with the old cap and rotor. Also would this cause the timing mark to flucuate and then the MSD failure I think so!

Thanks,

Bill
 
Thanks to all that offered help and sugestions.

I took out the distributor and checked the reluctor, cap and rotor. The rotor tip was to far away from the edge of the cap which caused arcing inside the cap and overworking the MSD unit. I put the old cap and rotor on with the new unit. Fired right up as did the other times. Went on a test drive and no issues! I'm pretty sure that was it.

Thanks again to everyone!

Bill
 
74 Slant Six said:
Thanks to all that offered help and sugestions.

I took out the distributor and checked the reluctor, cap and rotor. The rotor tip was to far away from the edge of the cap which caused arcing inside the cap and overworking the MSD unit. I put the old cap and rotor on with the new unit. Fired right up as did the other times. Went on a test drive and no issues! I'm pretty sure that was it.

Thanks again to everyone!

Bill
Click to expand...

Well that didn't last too long it did the same thing again! I have to tow the car home later and take everything out again. The frustration level is going thru the roof. I will try a new box and a different distributor. Is there any way to check to see what is causing this? Everything works great then all the sudden it cuts out and won't restart. Wiring is correct, could the distributor cause this by making the MSD unit work to hard and cook itself? This should be simple all of the old wiring has been removed the only connections I have are 2 wires to the battery, 2 wires to the coil, 2 wires to the dist. and 1 wire to the run posistion on the ignition. Any help would be greatly appreciated.

Thanks,

Bill
 
Instead of taking everything out AGAIN, have you tried the test to make sure the box is good or bad?
 
74 Slant Six said:
Steve,

How do I check the box to see? I have no spark from the coil.

Thanks,

Bill
Click to expand...

You won't get a spark without this test. With the key off, you need to disconnect the coil wire from the dist and put it near a ground, disconnect the violet/green wire plug, put a jumper wire in it(box side), turn the key to on, and then slowly pull the jumper wire out of one side of the plug. If you get a sound/spark out of the coil wire, then the box is good.


http://www.msdignition.com/page.aspx?id=3206

Also, you need to have the blue wire from the ignition switch wired in as well as the brown to the small red wire.
 
redfastback said:
You won't get a spark without this test. With the key off, you need to disconnect the coil wire from the dist and put it near a ground, disconnect the violet/green wire plug, put a jumper wire in it(box side), turn the key to on, and then slowly pull the jumper wire out of one side of the plug. If you get a sound/spark out of the coil wire, then the box is good.


http://www.msdignition.com/page.aspx?id=3206

Also, you need to have the blue wire from the ignition switch wired in as well as the brown to the small red wire.
Click to expand...

Thanks Steve I will try it when I get the car home. I only have the brown wire run to the MSD unit. Without the blue wire could this be the issue? And where do I trace the blue wire from? Is it the same blue wire running to the altenator?

Bill
 
74 Slant Six said:
Thanks Steve I will try it when I get the car home. I only have the brown wire run to the MSD unit. Without the blue wire could this be the issue? And where do I trace the blue wire from? Is it the same blue wire running to the altenator?

Bill
Click to expand...

It's the original blue wire from the bulkhead to the ballast resistor.
 
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