Which part of my ignition system is dying?
 

So here's the situation: The car was having a crappy idle and I had some CIS boots that looked pretty bad. So in November I replaced all the injector seals and boots and whatnot on my CIS system. I ended up having to drop the engine to get it back together and I had had several threads where I couldn't get it to run. Turns out I still had a vacuum leak. Finally got the car running (kind of) last week and took it 50 miles to a real Porsche mechanic to dial in the mix.

He can't seem to get it dialed in and worked on it for a while. He tested the plug wires and insists that they need to be replaced before further testing. OK, no biggie. Read on...

The car is an 83 SC with an MSD igniton, blaster coil and Magnacore wires (mech says they suck). Plugs set to stock spec by the mechanic last time I was up there. MSD was installed 5 years ago and it's been running well for years, until this summer.

On the drive to his shop cruising at around 3000 rpm, the tach started jumping. 3500-4000, erratic. When I hit the surface streets, it would be close to "idle" (~1000) but show 3000 on the gauge.

We pop off the cap and the rotor is melted!! Replaced the rotor and cap and did some more diagnostics. He says the car is missing which is why he can't dial in the mix. He claims to have been shocked by the plug wires when touching them. The snap on timing light is showing crazy crazy numbers. When you move the plug wires, it changes from idle to give off ridiculous figures...3000, 1800, 5000. He sprayed down the wires and we couldn't see any arcing. My homework is to replace the wires.

On the drive home about 30-45 minutes, the crazy tach thing starts again. Since traffic is terrible I stopped for dinner and let the car cool. It started up fine and I drive home with no further issue. When I pulled off the cap, the rotor is melted again.

What's killing these things? Which part of my system? I did some reading here tonight and apparently high resistance can cause this issue of melting the resistor on the rotor. Could these Magnacores be causing high resistance killing the rotor? What's making the tach go wild? Could it be the MSD unit itself? I wonder if it just worked enough and when I took the engine out I disturbed the "force" making the plug wires work on their last legs. What do you think?


Original rotor (2005-2009)
http://img690.imageshack.us/img690/2...3565910236.jpg

New/used rotor (December 18, 2009):
http://img32.imageshack.us/img32/776...3596519530.jpg
http://img32.imageshack.us/img32/39/cimg43606469051.jpg

High resistance gives low current and that won't melt the rotor only high current passing through would. High current comes from a shorted cable or shorted plug or I don't know how but the coil is putting out too much voltage. You might be able to measure a shorted cable / plug which would definitely cause your engine to miss.

You need a rotor without the RFI suppression resistor, to begin.

Magnecor 8.5mm wires are VERY good but somewhat fat. This requires extra diligence in making sure they are properly seated on the cap and coil terminals.

Anything I could do at home? He hooked up a scope and said the failure was consistent. I didn't write anything down and spent too much time near the tailpipe to remember exactly what he said.


How'd I make it 5 years with this set up? Just lucky?

Car has been back together and I built a couple of those "resistorless" rotors. Car experienced one episode of jumpy tach in March and has been solid until today. After an hour cruise, it was acting up again. I checked the voltage it was *solid* at 13.7. (been cruising with a multimeter for months) so I'm not suspecting the Voltage Regulator. I let it sit for a hour and drove home (with no issues :rolleyes:) measured When I got home I took off the cap and the rotor has blown out a bit and had melted some of the plastic of the cap. Had even gotten hot enough to fling some (a tiny bit) of the solder I used against the side of the cap.

Is it the coil blowing this out? Its about the only part I haven't replaced in this ordeal.

Steve,

Somewhere,........somewhere in the secondary path (plugs, plug wires/connectors, distributor cap, rotor, and high voltage coil terminal), is a high resistance and THATS the source of your trouble. IMHO, its not the coil or ignition unit. Something is not making a good connection and that resistance is the root cause. Plug gaps should be .040-.045.

We run a LOT of cars with the identical configuration without burning anything up.

Thanks Steve. Since we last spoke, it's been to a 2nd mechanic who set the mix for me and looked it over. I cleaned all the grounds. I sent the wires to Magnacore who tested them and found them OK. I have replaced cap and rotor (obviously :) ). The only thing left is the coil, and I guess, the plugs.

What do you set plugs gaps at for the MSD? If set at stock (they are), could that cause the issue? Mechanic 1 re-set them at stock last summer before all the trouble.

They are NOT set to stock.

Yeah, but if they are, it's not going to produce the problem he's having. A big gap is just more resistance and higher voltage in the wire. So, with a factory gap setting, you may not be getting all that MSD and Blaster can offer, but you're not going to burn anything up.

OK, I don't know all that much about this subject, but I happened to corner Richard Clewitt this morning and what I said there is what I learned today.

VA Steve, did you do what Steve@Rennsport said and make sure the wires are in direct contact with the cap and coil connections? A "spark" inside the terminal connections can make for that high resistance.

Now, what about that Blaster coil? Should you swap that out for a known unit?

What is the condition of the Green Wire that triggers the MSD?

This is the part number from NAPA for a solid copper rotor. That would help EP-407. High spark voltage needs good, solid connections or they find something to burn up, no resister stuff with MSD.

They all were seated OK on the cap and the coil. Terminals on the coil were tight.
Like I said though, it's intermittent. Drove home, fine, drove around the neighborhood fine. The only variable seems to be this manifests (occasionally) after an hour or so cruise.



It's a thought. It has been suggested to swap the voltage regulator as well, but it would be nice to know the cause without throwing a bunch of parts at it. And maybe the wrong parts. :( I'll probably order both, nevertheless.

It's in pretty good shape, but I put a new end on it about 5 years ago when I dropped the engine for some cleaning. The new end looks nice and clean like the day I put it on.



EDIT: I looked a little closer at the rotor and tested it with my multimeter. Recall that this is one of the ones I did the "mod" to. I actually got no connectivity from the center to the edge. There was a hairline fracture, I guess it got hot and the solder broke. (I will have to order that NAPA part, thanks James Brown).

The question is, WHY is this happening? As suggested, is my voltage regulator acting up, throwing in extra voltage, destroying the rotors and making me suspect the ignition system? This would be fun if it wasn't so frustrating.