Condenser failure

[bluez]

So my 12/70 Z is giving me some issues (stock ignition). I haven’t started it for several weeks, (ran fine back in August) tried last week and no go. Car started and was cutting on/off, tach was jumping all over the place. After a few minutes it wouldn’t start. Removed dist cap had spark at points, pulled plug #1 initially saw spark, then nothing. Removed coil and found oil on primary wire and coil. Coil looked to be original, so I ordered a new one as well as a new ballast resistor, still no go.  Today, I picked up a new condenser, checked for spark at the plug, all good, installed plug and tried to start it, it fired for a second then nothing, pulled plug found no spark again. Am guessing I have short somewhere? Is this a common problem? Thanks.

[SteveJ]

Show how everything is wired with clear, detailed photos. How did you test the plug for no spark? What is the voltage on the coil with the key in ON? What is the gap and dwell on the points? 

[Zpenman]

Try another new condenser, purchased from a different source than your last one. Last year I had some vexing ignition problems on my '71, and finally concluded that it was my condenser. The car actually ran for a while after the second condenser replacement, but then quit with no spark. Finally switched out to a Pertronix coil and inductive pickup, and it's been running fine since the switch. Still using the original dizzy. If you stick with the original setup, have found that the Delco condensers seem to be the most reliable.

[bluez]

Okay, here’s some pics. Car ran fine previously, nothing changed until now. Points were set earlier this year, I recall 50mm.

Will test condenser shortly.

[bluez]

As mentioned earlier, had removed #1 plug and saw spark for a brief second, then nothing when grounded.

[Zed Head]

Use a meter or test light and determine where you're losing power to the system.  If you have power everywhere, check the ground on the other side of the points.  Basic electrical system testing, power and ground.  Check power with the key at run and start since the ballast resistor has two circuits through it.

Spark can be lost by either no power or no ground or constant ground.  So, confirm also that the points circuit is complete when they are closed.  Also, check that the condenser is not shorted, via testing resistance through it.  Apparently, like many new aftermarket parts, condensers are getting poor even new.

Sounds difficult but once you start poking around and getting data it's easy.

[SteveJ]

Do you have the polarity correct on the coil?

[cgsheen1]

Don't fixate on the condenser. In fact, remove it until you get your spark problem sorted. It's job is to help eliminate radio noise, not make the coil spark... But, you can see from the above schematic that a bad condenser can permanently or randomly GROUND the coil thereby negating the operation of the points. You don't need it (you may want it, but you don't need it...). If you remove it while troubleshooting, it's one less variable.

(thanks for the comments and correction - edited the above to make a bit more sense)

Edited October 20, 2024 by cgsheen1

[240dkw]

1 hour ago, cgsheen1 said:

Don't fixate on the condenser. In fact, remove it until you get your spark problem sorted. It's job is to help eliminate radio noise, not make the coil spark... But, you can see from the above schematic that a bad condenser can permanently or randomly GROUND the coil thereby negating the operation of the points. You don't need it (you may want it, but you don't need it...). If you remove it while troubleshooting, it's one less variable.

Ok that is wrong, the condenser on the point are needed to stop the points from arching when they are opening. You can run it without the condenser to see if that is the problem, but long term will cause heavy pitting on the points and failure. The condensers on the ballast resistor and on the alternator are for eliminating noise. No sure when you bought you condenser from, but I had three in a row all fail with in five minutes of running. They were from Rockauto (Made in China). Bought some from Napa(Made in Mexico) and still running strong.

[Zed Head]

1 hour ago, 240dkw said:

Ok that is wrong,

Your comment about wrongess is wrong.  WRONG!  Just kidding.

Actually cgsheen's comment was only partially WRONG!. Disconnecting the condenser is a good idea.  The points won't "burn" immediately.  And the part about grounding (shorting) is RIGHT also.

Commenting about somebody's wrongess almost always goes wrong.  Like this post probably will.  Right?

[240dkw]

2 hours ago, Zed Head said:

Your comment about wrongess is wrong.  WRONG!  Just kidding.

Actually cgsheen's comment was only partially WRONG!. Disconnecting the condenser is a good idea.  The points won't "burn" immediately.  And the part about grounding (shorting) is RIGHT also.

Commenting about somebody's wrongess almost always goes wrong.  Like this post probably will.  Right?

Sorry, you are right, that was a poor choice of words. 

[Zed Head]

I was trying to be humorous but came off as scolding.  Sorry about that.  I'm sure that cgsheen just got his condensers mixed up.  He knows a lot more about electronics than a simple condenser problem would require.  Some of it's in his sig.  

Still waiting for bluez to give us an update...