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Crotchety Old Bastard
 
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Voltage to Coil?

Seemingly simple question that I have not been able to find in my manual - what is the voltage supplied by the CDI unit to the coil?
Thank you in advance.

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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 05-29-2012, 10:31 AM
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Brian

280V-480V

That's what I have heard once too. Here is a german shop who repairs HKZ. Only in German, sorry... but nice info there:

Reparatur Bosch HKZ für Porsche 911 und 914/6
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Roland

930 Turbo '81 Too many modifications to list
Old 05-29-2012, 11:10 PM
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Crotchety Old Bastard
 
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Thank you Roland. Wish I could read German about now, ha!
System voltage is of course 12V. What I need to know is how many volts the CDI sends to the coil.

On another note, was it you that emailed me about a GT3 zork? If so you can simply replace the muffler body on your system with a bypass pipe.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 05-30-2012, 04:03 AM
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Google Translate

German speak is back wards but you can figure it out

Stefan
Old 05-30-2012, 04:06 AM
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Quote:
Originally Posted by RarlyL8 View Post
Thank you Roland. Wish I could read German about now, ha!
System voltage is of course 12V. What I need to know is how many volts the CDI sends to the coil.

On another note, was it you that emailed me about a GT3 zork? If so you can simply replace the muffler body on your system with a bypass pipe.
Brian

I do not said 12V...? It's 280V-480V that the CDI sends to the coil as I said before, so be careful. It only hits you once...

No, email was not from me (In Switzerland you will be shot if your car is that loud)
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930 Turbo '81 Too many modifications to list
Old 05-30-2012, 04:56 AM
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Crotchety Old Bastard
 
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Are you saying that if I put a tester on the tiny yellow (+) wire where it is attached to the coil and turn the key to "on" the tester should read 280V-480V? I thought that was the voltage exiting the coil to the distributor.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 05-30-2012, 09:33 AM
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Brian

Yes that's primary circuit. Secondary tension from coil to Distributor/spark plugs is 28.000V to 48.000V!!!

That's the reason HKZ coils are very unique ones. So being careful is highly recommended
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Roland

930 Turbo '81 Too many modifications to list
Old 05-30-2012, 12:08 PM
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Crotchety Old Bastard
 
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What is the proper way to check voltage at the coil?
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 05-30-2012, 12:17 PM
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According the link I posted you should not check voltage in cause of the risks. Further symptoms of faulty coil or HKZ box can be very similar. Due the different circumstances under load is a test of the coil not saying much. They recommend to change coil when box is replaced. As it's dangerous to life, you better not check voltage at the coil!!!

Search someone who is familiar with the Bosch HKZ (Mercedes shops are nice) they have the needed equipment to check
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930 Turbo '81 Too many modifications to list
Old 05-30-2012, 12:29 PM
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Quote:
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Google Translate

German speak is back wards but you can figure it out

Stefan
Or use Google Chrome browser which will offer to translate as soon as you load the page.
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Old 05-30-2012, 01:02 PM
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Crotchety Old Bastard
 
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Too late for the caveate as I already checked the voltage to the coil, which is why I am posting the question.

The problem I'm chasing is a no-start due to no spark. The voltage I am seeing at the (+) coil terminal is 6V with the ignition on and CDI buzzing. Put tester on the battery and see 12V as expected. An electrician I am not, especially when it comes to complicated car wiring. A lamp I can handle ...
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 05-30-2012, 01:51 PM
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Crotchety Old Bastard
 
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Well as I live in a town called "rocket city" which has the most PhD's per capita in the US you can't throw a rock without hitting an electrical engineer. So with hat in hand I picked up the phone.
I now know more than any man has the right to about CDI ignitions.
Long story short you cannot measure voltage at the coil with the equipment I was using, and I really didn't need to do that anyway. All I needed to know is if the coil is getting power.
Went out to the car, wired the coil back up, grounded the spark plug on the A/C compressor, hit the key... and the car started and RAN. No intercooler, rags in the intake, spark plug hanging out the hole and this thing runs???
Quickly buttoned her up and went for a drive. Great to have a running car!
The culprit? Bad (+) wire connection to the coil.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 05-30-2012, 05:23 PM
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The primary voltage to the coil is not continuos like from a battery or wall outlet, it's real fast short duration capacitive discharge pulses so you can't measure it with a regular voltmeter.
I don't know what you would use to measure it, maybe an oscilliscope?

Most capacitive discharge ignitions supply the coils primary windings with around 450 volts or a little less. The coil is a step up transformer that increases that voltage in the secondary windings alot so it fires the plugs.
Old 05-30-2012, 05:57 PM
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Crotchety Old Bastard
 
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Yes Jim, I now know an oscilliscope is needed to measure discharge voltage. I also know where to borrow one should I need it, which I won't. No sparky you hit the trashy. I'm a simple guy.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 05-30-2012, 06:19 PM
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What kind of coil are you using? I had one of those silver brazilian ones die on me after about 2 weeks...
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Old 05-30-2012, 07:00 PM
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Crotchety Old Bastard
 
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Stock coil.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 05-30-2012, 07:52 PM
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Stock means the first one or just Bosch/Porsche?

Just because I had one (OEM from Porsche) from Brazil too some years ago, which died very soon and was leaking oil. Very poor quality

Glad to hear your car is running again.
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930 Turbo '81 Too many modifications to list
Old 05-30-2012, 10:40 PM
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Crotchety Old Bastard
 
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Stock as in the original unit.
Thanks yes it is great to have 'er back and running better than ever.

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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 05-31-2012, 04:02 AM
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