SC plugwire issues, backfiring, dying, etc
 

3 times in the last few weeks my daily driver (1980 SC) has decided to die on me, twice while driving and once while sitting. Symptoms were sudden catastrophic loss of power, machine gun backfiring through the pop off valve, no throttle control, yadda yadda. You can skip to section 2 if you don't care about symptoms, or section 3 if you just want the Cliff's Notes.

First time I parked the car, and 2 days later it started right up and was fine, even on a 200+ mile tear through the countryside. I had driven through some very heavy rain the night before, and assumed it was water messing things up, which cleared up after 2 days covered.

Second time was driving home from work. Pulled the distributor cap and saw nothing obvious, pulled the pug wires, again no water or anything. Saw that the O2 sensor wire was abrading on a pipe, messed around with connecting/grounding/disconnecting/fixing the wire, and thought I was able to create and stop the symptoms, so figured I had solved it.

Third time was right off the bat after being parked all day. Finally sat down this weekend and dug deeper in. I'm hoping that one of you could verify that what I found was enough to kill the engine.

Section 2
Checked fuel pump and relay, both fine. Checked battery connection, fine. Checked CD box, whining like normal. checked distributor cap again, found faint carbon trails around #2 inside the cap, and carbon trails going from #2 to the clip on the outside that holds the cap down (the one deeper inside the engine).
Pulled #2 plug, seemed a bit carbony, but not bad. Used #2 plug to test plugwires for spark, got good spark with #1 and #3 wires, but not #2 wire. Checked coil and coil wire, passed tests. Probed #2 wire for resistance, got varying quality. Cleaned up plug wire tips, distributor connections and rotor with sandpaper. Was able to get good spark on #2 plugwire now. Reconnected everything, made sure it was all tight, and fired it up. Symptoms gone, car ran better than it has in months.

Section 3
Cliff's Notes:
Car experiencing severe loss of power, backfiring into intake, strong gas smell from exhaust, and dying on idle. Symptoms come and go randomly.
It's been exceptionally humid here lately.
#2 plug wire seems to be toast, carbon trails seen in and around distributor. Wires might be stock, which makes them 30 years old and 135K miles. Standard Beru style, ground strap clad wires.
After cleaning/retightening everything, symptoms gone (for now).

Would a missing/ arcing wire be enough to kill the engine, make it undrivable, and cause massive backfiring into the intake? I would expect that losing a single wire wouldn't be THAT severe. Could it have been arcing/crosstalking or something bad enough to cause that? Am I going to fix/replace everything and find that the issue is further upstream in the ignition system? I saw no damage along the path of the other 5 wires and plugs. I cannot see how something upstream can be plug dependent (ie. bad CD box or coil).

I have ordered new cap, rotor, wires (Magencor), plugs, and a MSD blaster coil (I plan to go MSD soon anyways).

Thanks!

Mike - I agree that's a lot to be caused by one bad wire. Maybe the wet weather on the bad wires. You can try watching the wires in the dark to see how bad they are. Or test continuity. The Beru ones have the resistance marked on the connectors. My motronic has 1K in the distributor connector and 3K in the plug connector. Ken

One of the problems with the Beru wires is the SS braiding that hide cross over arcing from broken down insulation. The new wires will fix that. As with any CD system, carbon tracks need to be eliminated due to the high voltage. Try to go out to the car at night with the lights off and see if you can see any sparks jumping around off the wires. Mist a little water on the wires and see if you can duplicate the stalling. Not sure if a new coil will do anything for you other than have it ready for the MSD swap. try just the wires first and see what that does for you. then the cap and rotor, then the coil. See my post on "cis to carbs, let the fun begin" for MSD swap info. Oh and have fun!!

i recently had this problem post heavy downpour.
-Removed ignition distributor for cleanup. Nil fix.
-Replace Distributor cap. Nil Fix
-Inspected HT leads. Nil findings.
-Inspected LT leads, found corrosion on wire feed to Hall effect sender. Cleaned, reconnected with silicon grease, Nil fix again.

Only when i removed the alternator did i solve the problem.
Basically, upon removal of the assy, i noticed that the ground wire from the alternator to the engine casing was not connected.

Thing is, this car has been operating like such with no problems anyway.
But it was only until re-installation of the connection of the alternator, did my issues finally get resolved.
I guess the rain may have caused some corrosion on the connections there.

My suggestion is run the engine with a voltmeter connected to the battery.
Mine showed a drop in volts each time prior to the car running erratic and finally shutting down.

However in my case, when it rains here, its a heck more than in the states. So i guess ingested of water into the Fan assy was a likely suspect.

Thanks for the ideas guys. I didn't even think about a bad ground.

However...my symptoms have changed :D

The last 4 times I've tried to start the car (every time), it has had problems, but new ones.
It will either no-start (but you can tell it's trying to fire, so I'm getting at least some fuel and spark).
It will fire, but run poorly, no throttle response, backfiring, but I can keep it running if I feather the gas just a bit.

Or, after turning the key 8 jillion times, it will fire right up, no problems.
If I turn the key maybe 20 times, I'll get 10 no starts, 9 barely starts, then one perfect start. In fact, the first time, it suddenly went from barely running, kept alive by feathering the throttle to *click* perfectly running. I didn't turn it off and start it up, it just literally seemed to click on. The other times, I had it barely running, turned it off, immediately turned it on and it started fine.

This sounds suspiciously of a CD box problem. It whines no matter what, but it might not be feeding the coil. Of course, the MSD box is the only thing I *didn't* order 2 days ago...

So, questions:
1) What feeds the CD box the signal to fire? Is there a crank sensor or something? (EDIT: I know there's a signal from the dizzy, I don't know where it is or how it connects to the CD box, nor do I know what's inside that might be busted)
2) I disconnected the CD box this weekend via the 6 pin connector. I am pretty sure it's connected properly, but if that was slightly wiggly or loose, could it cause these start/nostart issues?
3) Each time that i got it running, the car ran flawlessly for the 20-25 minutes drives. If the CD box is going wonky, why wouldn't I get random issues while driving? Why would it only be bad when trying to start the car?

Thanks again everyone!

The infamous green wire is what sends the signal to the CD box, isn't it? If that wire was cracked/rubbing it would cause my issues, wouldn't it (not discounting other things, but that would seem to be enough to garble the signal to the CD box, which would then not fire/misfire).

The hall sensor in the dissy is used to trigger the CDI unit via the green coax wire. Take a look at mine, and it ran great for the 20k before I replaced/found it. Porsche used the coax cable to suppress EMI emissions in a nuclear war environment! Anyway, when you get it to run, put a induction timing light on it and watch what happens when it starts to sputter/stall. Wiggle the green wire, check the dissy for side play around the pickups, remove the green wire from the dissy by pulling the metal pin (small screww) from the plug on the side of the dissy and check it between the CDI plug and the dissy plug for opens/grounds. It might very well be a CD unit but first eliminate all the other things first.
http://forums.pelicanparts.com/uploa...1279739793.jpg

Thank. I'm learning the whole ignition assembly here via trial by fire...

My only fear is that I'll replace the cap, rotor, plugs, wires, coil...then the green wire, CD box, and still have issues, which means (I suppose) that the problem would lie deep inside that distributor...

I did find the link to the 30 inch 928 green wire replacement, which I'll consider if I find any damage on mine.

Updates:
Replaced the plugs, wires (Magnecor 8.5mm), cap and rotor, and coil (MSD high vibration).
Pulled the dizzy and checked the green wire, got 600 ohms (actually something like 618) across the pickup as measured from the CDI harness. Probed the wire end to end, got proper numbers. Took the wire and tried to twist/distort it a bit, and couldn't get a short between the center and braid conductors. Wire is intact, but plug inside dizzy looked like it would disintegrate if i looked at it too hard.
CDI box has battery voltage on pin 15 when ignition is on. Couldn't check the varying pulse when cranking, since I had to helper.

Seems better, but I'm still getting poor/non-starts. I have ordered an MSD box and new green wire since I'm tired of screwing with this. The only thing that could be left is random shorts across the green wire, random CD box failures, or the actual pickup inside the dizzy is randomly breaking and fixing itself.

I figure after the MSD box and wire, I'll have replaced all of the pieces of the ignition that have any current running through them. If that doesn't fix it, I'll burn the car down.

Please PM me before you start the fire...I'd like to see that.
Are you still sure its the ignition? Still smell gas out the exhaust? When it is stubborn to crank have you tried a squirt of carb cleaner or such to see if it pops? Let me know if you need a hand. Ken

My symptoms were a little different than yours but I had a CD box failure even though the box still made a high pitched "whine". Can you swap in a known good one?