1978 911 SC Coil Question

[opticalfuel]

What's the skinny on coils? Which is better? Bosch or Jacobs?


Are there any upgrades to that unit that would make sense, and make the car run any better?

How about the CD unit?

Isn't it: The more spark the better?

[jfw834]

i'm not that familliar with what is the best performer, but i have read that a popular upgrade is the MSD coil and box. look it up under recommended upgrades here at pelican.

EDIT: here is the link...

http://www.pelicanparts.com/catalog/shopcart/911M/POR_911M_uprc91-detail.htm

[KobaltBlau]

depends on which ignition box you are using. you should search for coil or "blue coil" or "msd coil" or something.

Most like the MSD for an ignition upgrade, used with the MSD coil. I personally don't think this is needed with a mostly stock engine, but may work well for a modified one.

Some say the CDI box will only work with a CD coil, others say that the bosch blue coil (or some other coil they like) is OK. I happen to have a bosch blue coil on my SC with stock CDI box, and it definitely works, but I may be shortening the life of my CDI box or getting suboptimal performance. Let's not start that debate back up again here.

[Superman]

I am told that, technically, the stock Bosch CDI system coil is not a coil. Looks like one, probably acts like one, but is not used as a "coil" in the traditional sense.

[beamonk]

Don't get one of those cheap Bosch silver coils, I am going through my third right now. It is leaking goo again. going to MSD high vibration this time.

[stlrj]

If you're going to that much trouble you might as well convert to HEI: http://dimequarterly.tierranet.com/articles/tech_hei.html

I did the conversion on my 78 3.0 and never had a CDI issue again.

By the way, Bosch DME ignition is essetially the same as HEI which is your basic transistorised ignition system found on every car today.

Cheers,

Joe

[blue82coupe]

As stated above ...stay away from the silver Bosch coils. Been through(2) myself, on a previous engine. If you go with MSD you will use the blue Bosch coil.

[emcon5]

The stock CDI puts out plenty of spark.

It has come up in the past that the MSD "high Vibration" blaster coil has the same turns ratio/voltage and can be used as a direct replacement for the stock coil. Details here:

MSD Blaster coil?

In other words, if your Bosch coil isn't broke, don't fix it. If it is broke, replace it with a $59 MSD.



It needs to be the High Vibration version if you mount it in the stock upside-down location. The standard one needs to be upright.

Tom

[opticalfuel]

Ok. Understood.

How does one know for sure it's time to replace the stock coil?

I still have a rough warm-up issue. It is not the WUR. I know that because I purchased a new one within four months, and it does the whole 2000 RPM for 2 min, and then down to 900 or so. The problem is:

After that it struggles to maintain a nice idle, till it is actually showing about 180 deg on the gauge.

Question:

Could the coil be bad if in fact the car runs fairly smoothly at speed and revs all the way up to 7K without much problem?

I think I might indeed have a small vacuum leak, which is proving difficult to locate. No amount of spraying carb cleaner in the areas of the throttle body (external to the airbox of course) make the idle increase by any noticable amount.

It is kind of a stumper. I can live with it, but it'd be nice to figure out what is making it struggle on warm up. It searches for an idle pretty rapidly and sometimes acts like it might die, but at least it isn't dying. (it goes high, low, high, super low, and then sometimes reaches a somewhat stable idle.)

Any ideas of what to test or clean? I was considering taking the injectors loose and cleaning them in the ultrasonic.

Changing the sparkplugs, cap and rotor has done wonders for the car.

The coil has not been replaced since I have owned the car, which is about 5 years. I am sure they last longer than that, but it looks rather aged. Anyways, it isn't that much of an investment to just be sure.

Thanks!

[Early_S_Man]

The coil is not the problem if engine runs fine to redline after warming up!

To be sure, if the coil is leaking brown tar or oil, it is time to replace it ...

There are original 1969 CDI systems out there that are still performing up to spec after 36+ years with the original coil!

One thing you want to be sure you NEVER DO ... don't crank the engine with the coil wire to the distributor pulled out! That is a sure recipe to kill the coil, an d possibly the CDI unit as well ... you must always have a spark gap present as a load on the ignition system!

A few things to check ...

1. Check the ignition advance curve in the distributor when cold [from 900 rpm to 4000 rpm in 500 rpm increments -- plot a graph or fill out a chart] and when fully warmed up, do another chart or graph ... any difference is a good reason to R&R the distributor, clean it up thoroughly after partial disassembly. Sticking advance mechanism can definitely affect warm up performance and power!

2. If you really believe ignition is an issue while warming up ... take the car to a shop with a Sun Analyzer (or equivalent) ignition scope and have it checked while warming up from dead cold.

[opticalfuel]

I can have it checked. I replaced the ignition distributor about a year or two ago and it was a pretty penny.

It might be sticking a bit though. Do you suggest that I spray something like WD40 into the Ignition Distributor? (into the area under the rotor?)

I also notice that the vacuum diaphram part on the distrubutor (the part that is silver, round in shape and bolted on the side of the distributor) is somewhat loose. I don't know if it is supposed to be rock solid, or is should have some play.

The thing that would make sense to me is that the idle and advance could be affected by the 'play' in that mechanism. Is my thinking correct?

[Nitrometano]

MSD Vibrator is the one!!!

[opticalfuel]

Is the only way to lubricate the advance mechanism to pull the distributor out of the motor and partially dissasemble?

Can I remove the screw in front of the vacuum advance bulb, and pull it back enough to spray some lubricant in there with a can of WD40 or 'Dupont Performance Dry Lubricant' with Teflon Fluoropolymer.

I can use a red mini tube with the spray to inject some lube into the area where the vacuum advance mechanism is.

Does anyone know of any reason why lubricating with the above mentioned products or in the location I mentioned would be harmful?

[Nitrometano]

Taking apart and disemble the ignition distributor is not difficult. You will need patience and remember how to put back the parts into the same order that you dissemble. Use a liberal dose of lubricant and moving the parts to take off the rust and dust. Then wipe it and clean again with lubricant. I do that to a 1978 911 SC.