MSD high vib coil with stock CDI
 

Hey guys I searched and read bunches of posts all over pelican and the internet.


I am tracking down a spark issue with my 84 and bought the MSD coil. At first I thought I didnt need to add a resistor but then I saw a post that said I did.

I ordered the big voltage dropping Ballast resistor from MSD, but now Im not sure if I need to use it or not. It is not trivial to find somplace tidy to put it out of the way under the IC.


Does anybody have any definitive insight on this.

Thanks
Aaron

since you have one i would try it with and without.
ballast is for current limiting or reducing.
the MSD coil DOES have a lot less primnary resistance than a bosch but with a CD that may not matter.

how do you know it is spark related

could be
air leak
injector
plug wire
fuel dist
compression issue
valve issue

Thanks, the car just quit running and I pulled a plug wire and put in a plug to check for spark, there was nothing there

I was going to try with and without but I thought there might be long term differences with reliability of other components. Also the Resistor is bigger and more difficult to place than I expected. It will take a bit of work to put it somewhere tidy.

if the CD is good you can put the MSD coil on with no ballast and it will run.

check for power at the CD with the key on.
if you have power and have swapped the coil then the CD unit is bad.
well i say that. there is always a chance the coil in the dist is bad or the wrie from the dist to the CD is bad.
at the CD unit, ohm the 2 coil wires to the dist. i think it is around 600ohms.
listen for a high pitched whine, if you dont have that then it is definately bad,

if no power to the CD there is a relay that feeds 12v to it. check that.
it is actially a delayed action relay. it is what keeps the engine running after you tirn the key off

The CDi makes the characteristic whining noise with the key on so I assume it has power.

My car being an earlier euro sometimes has less fancy relays than later usdm cars, though not sure if that matters here. I dont have a yellow relay for example

If the MSD coil fixes the issue should I go back and wire in the ballast resistor? I have seem some post that claim it can burn out the CDI unit if I do not.

THanks

Aaron

Call MSD and ask them.
They know what's reliable and works over the long run with their ignitions.

I wouldn't go for a long drive or trip in a car that might burn up it's original Bosch CD ignition box because the wrong impedance coil is wired to it.
The original Bosch 930 coil and MSD coils have different impedance. I think thats another word for the primary winding wire resistance.
The only other coil i know of that has the correct impedance for the Bosch CD box is the Permatune epoxy filled coil.

I had two MDS blaster coils fail on my 951 not using the MSD box. now back on the OEM coil for now.

my plans for my 930 build is to replace the old electromotive with a twin plug RSR dist, and two, MSD 6AL's, MSD BTM and two High-vibration blaster coils

good luck.

OK, I Just thought somebody here would know, especially because it seems to be a really common switch and our host sells them. I would buy an oem coil but apparently the new bosch ones have life expectancy measured in min.

really that is surprising the consensus on the 911 forum is that the new bosch coils are junk, it is of course a different application though

Also somebody credible in the main 911 forum said that the impedance and turn ratio is nearly identical for the bosch and MSD hi vib coil

The new Bosch ones are made in Brazil. From my experience they gradually leak oil and burn out when mounted upside down on the fan housing like the original one.

If you mount them somewhere away from engine vibration and heat with the tower right side up they will last a lot longer.
The Permatune epoxy filled coil is the correct impedance for the Bosch CD box and the Permatune replacement CD box, and it's black so it looks OK upside down on the fan housing under the intercooler.

i put a set of clewett wires on my car. but i had him make a special coil wire with a 90 on one end.
i now have my MSD coil in its original place but turned right side up. the 90 goes on the coil end.
to top it off, i have a 930 with the inter cooler right on top of the coil and i could still do this.
had to slide it down in the braket though.

the new bosch coils are not that good.
i thought they were china made.

i dont know if the impedence is the same but the MSD coil primary resistance is a lot less.

i am going to research this more.

look in the 911 side for thread about how much current does a CD draw.