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Quick CDI Sound Question

Iím still trying to sort out a no spark condition on a 1976 911 and I checked terminal 15 for voltage and it looks good but I donít hear a high pitched noise from the CDI. Iím wondering how hard it is to hear. My next question is whenever the ignition is turned on there is a humming/buzzing sound from some other sort of system that would drown out a lot of sound from the CDI in my opinion. Iím wondering if itís fuel or oil or what and if thatís normal.

Old 07-14-2019, 03:15 PM
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Originally Posted by GiantRider View Post
Iím still trying to sort out a no spark condition on a 1976 911 and I checked terminal 15 for voltage and it looks good but I donít hear a high pitched noise from the CDI. Iím wondering how hard it is to hear. My next question is whenever the ignition is turned on there is a humming/buzzing sound from some other sort of system that would drown out a lot of sound from the CDI in my opinion. Iím wondering if itís fuel or oil or what and if thatís normal.
The CDI charging the capacitors is much like a camera flash gun charging. Its not all that loud.

Sounds like your fuel pump is running when the key is on. Some of them can make a bit of a racket. Doesn't mean they're necessarily bad or suspect.

Not entirely sure when the connector that provides ground to the fuel pump (and thus inhibited the pump when the motor wasn't cranking or running) got added to the CIS air meter. Pretty sure my '77 had it. Maybe the '76 doesn't - or it was unplugged or otherwise bypassed?

Try pulling the fuel pump relay or fuse.
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Old 07-14-2019, 05:54 PM
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I thought that too and replace the relay and no change. Whenever I push bar in the air box I can hear the injectors going. I really think my CDI is bad.
Old 07-14-2019, 06:34 PM
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a working Bosch CDI makes a 3.6kHz whine noise. It's a clean sine wave tone. I would not consider this a buzz sound as the tune is much higher. More like the test tone from an old TV station.

If there is no sound coming from the box with the ignition switch ON and you listening with the rear lid up it either doesn't receive power or it needs repair

Ingo
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Old 07-14-2019, 07:45 PM
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The sound intensity of the power converter inside varies unit to unit. All in the 3.5 - 4KHz range. Sometimes it is pretty subtle, hard to hear if the fuel pump is running at the same time. If in doubt, you can remove, put it in a quiet environment, and apply +12V to the CENTER pin of the connector with the case grounded. If it still does not 'squeal', it definitely will not work in the car. If it does squeal, that's good, but that does not guarantee it will work because the converter is just one part of the device. It could have other problems, the most common being a dead discharge capacitor buried deep inside. These units are also susceptible to reverse-voltage events. Even a momentary reverse battery situation will take them right out.
Old 07-15-2019, 07:24 AM
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Quote:
Originally Posted by GiantRider View Post
I thought that too and replace the relay and no change.
If the noise you describe
Quote:
ignition is turned on there is a humming/buzzing sound from some other sort of system that would drown out a lot of sound from the CDI
is the fuel pump running with the key on, this could easily be loud enough to make it hard to hear the CDI. I could never hear my CDI over the fuel pump.

Replacing the relay doesn't help. Pull the relay temporarily to kill the fuel pump and check if you can hear the CDI then.


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Originally Posted by GiantRider View Post
I really think my CDI is bad.
Well, yes, that certainly can/does happen.
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Old 07-15-2019, 09:21 AM
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@GiantRider
Check out this vid of mine. You can clearly hear the CDI:

https://youtu.be/oES4XNNnWYU

This second vid is of the CDI sound (slightly different) after it was having a warm stall issue ~:30

https://youtu.be/_9kAjGGLTgk
Old 07-15-2019, 10:35 AM
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Quote:
Originally Posted by Nditiz1 View Post
@GiantRider
Check out this vid of mine. You can clearly hear the CDI:

https://youtu.be/oES4XNNnWYU

This second vid is of the CDI sound (slightly different) after it was having a warm stall issue ~:30

https://youtu.be/_9kAjGGLTgk
Wow thanks for that video that is tremendously helpful. Iím contacting shops to see if they could drop it in another car to test it but Iím also really interested in doing the MSD install
Old 07-15-2019, 07:12 PM
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Originally Posted by GiantRider View Post
Iím also really interested in doing the MSD install
More torque/HP and better long term reliability, right?
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Old 07-16-2019, 06:08 AM
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Before doing a MSD install check out Classic Retrofit's CDI+ Ignition which has dual spark at all RPMs.

Pelican Parts listing: Classic Retrofit CDI+ Digital CD Ignition Unit
Old 07-16-2019, 06:49 AM
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Before doing a MSD install check out Classic Retrofit's CDI+ Ignition which has dual spark at all RPMs.
Another big torque/HP gain here too, plus proven long life reliability, right?
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Old 07-16-2019, 03:39 PM
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That is my understanding but I have not used the product.
Old 07-16-2019, 04:13 PM
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Hey, nice marmot.
 
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Quote:
Originally Posted by HaroldMHedge View Post
That is my understanding but I have not used the product.
That was sarcasm from Loren. Ignore it.
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Old 07-16-2019, 05:00 PM
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A portable AM radio placed near the CDI will usually detect and amplify the inverter noise from stray radio interference not completely shielded by the case. In the case of my CDI, my hearing has degraded with age and I can no longer hear higher than 13kHz. The AM radio will pick up the higher frequencies and allow me to hear it plainly within my audible range. Fred


Quote:
Originally Posted by Bob Ashlock View Post
The sound intensity of the power converter inside varies unit to unit. All in the 3.5 - 4KHz range. Sometimes it is pretty subtle, hard to hear if the fuel pump is running at the same time. If in doubt, you can remove, put it in a quiet environment, and apply +12V to the CENTER pin of the connector with the case grounded. If it still does not 'squeal', it definitely will not work in the car. If it does squeal, that's good, but that does not guarantee it will work because the converter is just one part of the device. It could have other problems, the most common being a dead discharge capacitor buried deep inside. These units are also susceptible to reverse-voltage events. Even a momentary reverse battery situation will take them right out.
Old 07-18-2019, 12:17 PM
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Originally Posted by mysocal911 View Post
Another big torque/HP gain here too, plus proven long life reliability, right?
650+ customers would say so.

https://www.instagram.com/p/Bz_hPCklto9/?igshid=6vp1dk3xf83u

https://m.youtube.com/watch?feature=youtu.be&v=UtnrLj1pVF4&fbclid=IwAR1X6oBp1wObnSTDj-WJq9o73ROe1MAPUvsLDa7zW6-mX78R6QKnhx0jE14
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Last edited by Jonny H; 07-18-2019 at 01:43 PM..
Old 07-18-2019, 01:36 PM
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Jonny, Well done. I'm only at 151 units sold in 5 years and that being with a more varied market. You must be doing something right despite the criticism from one particular individual. From my testing with my own CDI, and experience, your design should produce more HP than the standard Bosch design whether it be the older 3 pin or the later 8 pin HKZ boxes. Good show! Fred
EDIT; For anyone that thinks it is total energy to the spark gap that makes power, consider this: My CDI on a 200HP hopped up VW engine made 6 more HP than a high energy magneto, with more stable AFR readings across the rpm range.

Last edited by Fred Winterburn; 07-18-2019 at 02:41 PM..
Old 07-18-2019, 02:35 PM
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Just a follow up on the problem being solved. It turns out that the problem was a bad CDI. I sent the CDI box in to Pelican Parts for a rebuild and I am very happy with the service they did. I was told that if the CDI was good that I would be refunded which is nice. The unit came back looking brand new and with a very detailed description of what was done. I was dragging my feet on getting my Porsche running again but I stuck the rebuilt CDI in there and it fired right up!
Old 10-05-2019, 11:31 AM
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Quote:
Originally Posted by GiantRider View Post
Just a follow up on the problem being solved. It turns out that the problem was a bad CDI. I sent the CDI box in to Pelican Parts for a rebuild and I am very happy with the service they did. I was told that if the CDI was good that I would be refunded which is nice. The unit came back looking brand new and with a very detailed description of what was done. I was dragging my feet on getting my Porsche running again but I stuck the rebuilt CDI in there and it fired right up!
That is good news. I have my Bosch CDI nicely stored in a box in a cabinet in my shop. My '73 MFI 2.7 really benefited from a switch to a modern CDI box. Much better starting, idle mid-range, upper RPM and a nice soft rev limiter I have set at 6600 RPM. Not sure if your '76 has points,but getting rid of them is a good idea too.

I use a Daytona- Sensors CD-1 with their coil and love it.

Remember the Bosch is a 50 year old design with 45 year old electronic components.

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Old 10-05-2019, 05:49 PM
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