Tracking the spark

What is the best "common sense" way to track the juice from the battery though the plugs? I just replaced a coil and the car still sounds as if there is no fire.

It will not start. It's as if I have the coil disconnected. I replaced each connection methodically and feel comfortable that I don't have an "idiot" mistake.

Did I mention that I don't want to purchase $500 worth of tools?

I am about to go to the shop and say "see ya when you have it running".

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Mark Isaak
'74 Targa

[This message has been edited by mark 74 carrera (edited 09-21-2000).]

Mark, pull a plug wire from the distributor cap and hold it about 1/2" from it's contact with a pencil or something non conductive. Have someone crank the engine over. Look for spark jumping between plug end and cap.

Mark,

Be sure to check/clean the 14-pin connector at the relay/fuse/reulator/CDI-unit console for any corrosion. Also the 3-pin connector at the CDI-unit.

If you have an analog multimeter or Voltmeter, check for 460 Volt pulses at the primary of the coil when the engine is being cranked. If you are getting good ground pulses (from the points in the distributor) at the input of the CDI-unit and nothing at the primary of the coil, then either the CDI-unit or your wiring is bad! You should be able to see the 'kick' on an analog meter, while cranking, even though the pulses are of short duration!

The troubleshooting hints at the Perma-Tune site might be helpful:

http://www.perma-tune.com/tech/911.htm

The wiring diagram shown for the Perma-Tune unit and your Bosch CDI-unit are identical!


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Warren Hall
1973 911S Targa

Everybody,

There is no juice to the new coil. There is no juice out of the CDI unit, but it whines. If there is power to make it whine, does that mean I'm looking at a new CDI unit?

Warren, I just went to the perma-tune site and read about the CDI being knocked out if your coil goes bad. After removal, my coil showed evidence of major leaking of the oil at the top main seal. The permatune site described my coil to a tee. It said that as a bad coil shorts out it sends a power surge back to the CDI which kills the CDI. Does this sound right?

If it is gone, any suggestions while I'm buying?

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Mark Isaak
'74 Targa

[This message has been edited by mark 74 carrera (edited 09-23-2000).]

Mark,

If you are ABSOLUTELY certain all of the connections to the CDI-unit, distributor, and coil are good, the CDI-unit is probabyly bad ... the same incident that cooked the coil probably got the CDI-unit too.

But, just to be sure the CDI-unit is getting good ground pulses, pull off the 3-pole connector at the CDI-unit, hook an Ohmmeter to terminal C on that connector, manually turn the engine over until the points are positively closed, and check continuity between Terminal C and a good ground. Then, turn the engine until the points are open, and check to see if the Ohmmeter is reading an open between Terminal C and ground. If those grounds and opens are getting to the CDI-unit input, and it is whining, and no 350-460 VDC pulses are coming out to the coil ... an oscilloscope could verify no pulses ... then the CDI-unit isn't working!

A Perma-Tune unit is a good replacement for the Bosch ... I have a spare that has been run on the engine for a week and I could tell no difference in the way the engine ran or responded. I have seen Perma-Tune's for $195 lately in Excellence, and also used Bosch CDI-units on eBay go for $60. But, it might take a while to find one come up on eBay again, as there are none currently!

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Warren Hall
1973 911S Targa

Warren, I'll do it! Thanks for your help. I do think the CDI unit is gone but I will try your suggestions to make sure.



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Mark Isaak
'74 Targa

Hold everything!

Did we forget to mention points?

What happens when you pry them open manually with a screwdriver. Does it spark?

Regards,

Joe