ignition breakdown @ 3000rpm when warm

[qwkstix]

Howdy Pelican Technical,

I own a 1973 T Targa that is a rose. I just brought her out of a 20 year nap because my kids finaly grew up and moved out! She awoke with a start up after about three cranks and off she went until recently. I am seeing an internittant ignition breakdown after warm @ 3000rpm, she is mechanicaly injected and has about 150K. She is going to super tech for a rebuild in Jan. 2011. This ignition breakdown is intermittant and fails @ 3000rpm warm, not cold, and has me stumped? All secondary ignition parts are like new as I put her away with it all renewed. I replaced the ignition amplifier (coil) because I knew it was original and it acted like it was breaking down, and was found to be cold after running for about 30min. When I feel it occuring and I shift to lower rpm's it stops till 3K is reached again, this problem being intermittant is what really stumps me and makes me think maybe injection. I checked the CD unit the only way I can and I hear it whining key on engine off. Points look brand new as well as all primary ignition does as well. I am a 28 year just retired master tech myself so you can be free to talk to me in an advanced fashion. I thank you guys in advance and think you @ pelican are the cats meow...........

Thankx
Kevin

[ischmitz]

My first question is what makes you say it is an ignition breakdown? If the car misfires when warm this can have a multitude of reasons. Mixture control can be off (WUR) or vacuum leaks can cause issues that are masked while the engine is cold (mixture will be richer).

If you really have an ignition failure there is one condition that can happen with marginal Bosch CDI boxes. The box latches up when hot. What happens is that the box stops producing any spark and the engine flat out dies. Once you switch the ignition off (power-cycle the CDI box) and re-start the engine will start but then at some point again flat-out quit.

To determine if you have latch-up listen to the whine of the box when switching the ignition to ON. It has a certain note (around 3.5 kHz). Once the engine dies in the above described fashion do not switch the ignition off but listen again. The whine will be at a much higher pitch (4 - 5 kHz) and not as intense. Once you power-cycle the ignition the tone of the whine will be louder and at a lower frequency again. If you can estabish that pattern your Bosch box needs repair

Cheers,
Ingo