Ignition coil voltage issue

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Jadewombat
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Ignition coil voltage issue

Post by Jadewombat » Fri Apr 29, 2016 1:14 pm

I'm running a 009 distributor with pertronix and having an issue with the (-) side of the ignition coil when cranking dropping from 12.1V static down and then jumping around in the neighborhood of 6-9V. I watched it with a voltmeter.

Tried changing the ignition coil from a Bosch blue unit to a Bosch black unit, brand new stock wires, used aftermarket CB wires, new distributor and pertronix, new cap, new rotor, tried running an extra 12V lead to the (+) side of the coil, etc.

The reason I'm concerned with getting the (-) coil voltage steady and higher is I'm running a MS unit and it's not seeing the spark and not turning the fuel pump on, etc.

Thanks.

Ol'fogasaurus
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Re: Ignition coil voltage issue

Post by Ol'fogasaurus » Fri Apr 29, 2016 1:29 pm

I have the same setup: 009, Bosch blue coil and a Pertronix conversion.

1) not all Bosch blue coils are equal. Some will take 12 volts and some require a voltage drop.

2) not all 009s are the same either. Some are better than others. I always recommend having the dist. spun and checked out on a Sun or similar machine. That is a check for bushings and innard components.

3) I had one suspected Pertronix unit so I changed it out and no problems. I now think it was not the Pertronix but something else.

Run a test wire from the battery ground to the coil to see if there is another problem. Grounds on even new cars are a constant problem much less an old tired metal bug of some sort. I do not rely on the pan any more but go directly to the block/tranny bolt then the wire to the pan. Can make a lot of difference.

This may not be any of your problems but might be worth a look-see.

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Jadewombat
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Re: Ignition coil voltage issue

Post by Jadewombat » Fri Apr 29, 2016 2:00 pm

Thanks Ol', will try your suggestions. A visual of the problem. This is measuring the (-) voltage.

http://vid52.photobucket.com/albums/g30 ... w70ncj.mp4

Ol'fogasaurus
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Re: Ignition coil voltage issue

Post by Ol'fogasaurus » Fri Apr 29, 2016 3:47 pm

Like I said: check the grounds first it is the negative side of things that is where all the work is done (quite a play on words there too). If the coil is weak on you and you have a voltage drop on it then the coil might be of the type where it is not needed. I know this is true on some of the blue Bosch coils but again, not all of them. The voltage drop could also be a problem assuming you have one.

Lee

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Jadewombat
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Re: Ignition coil voltage issue

Post by Jadewombat » Fri Apr 29, 2016 5:21 pm

Tried hooking up another ground from different points on the case to the same negative lead on the battery, no change in the voltage jumping around from 6-9V. Also tried both different coils, Bosch black and Bosch blue. Both coils, despite their age, have the same resistance of 3.5ohms.

What is causing the voltage drop and how does ohms law play into this with resistance in the system?

I do get spark and it looks fairly strong across the spark plugs.

Ol'fogasaurus
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Re: Ignition coil voltage issue

Post by Ol'fogasaurus » Fri Apr 29, 2016 11:35 pm

I may not have been clear. By using the word voltage drop I meant a dropping resistor from the ignition switch to the coil. Some of the blue coils need one and some have it built on or just don't need one.. I forget right now but I made sure the coil I bought did not need one.

Also, look to make sure the Pertronix is hooked up correct. I seem to remember that there is a distinct possibility of doing that. I think I got my unit back in the last century.

Lee

Ol'fogasaurus
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Re: Ignition coil voltage issue

Post by Ol'fogasaurus » Sat Apr 30, 2016 12:01 am

http://www.ratwell.com/technical/BlueCoil.html

Interesting: it mentions STF. It also says that according to someone they thought the black coil was better than the blue coil. I have heard that depending on the blue coil used it is the opposite.

Opinions are worth what you pay for them I guess. Some other bits that might help:

viewtopic.php?t=124069

http://www.pertronix.com/support/tips/

http://www.thesamba.com/vw/forum/viewtopic.php?t=344801

What ever I still would look at your coil and see if it is internally ballasted or not. If it is no dropping resistor or vice-versa. You just don't was two ballasts used.

Lee

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Re: Ignition coil voltage issue

Post by Piledriver » Sat Apr 30, 2016 1:52 am

The ms doesn't really care about that average voltage, which depends on coil input voltage under load, the resistance of the coil, and the "on" resistance of the power switch in the pertronix, the dwell//duty cycle built into the pertronix and to some extent the cranking RPM...
The (correctly setup for coil input) opto circuit only looks for the hv (~300v) kickback spike you get when the "points" open and the magnetic field collapses, and a spark jumps.
So spark?== no signal it can see.
There's a very high probability (if you have spark) that the $2 opto is bad.
VERY common failure part.
Make absolutely certain the circuit is correct for coil input--- It gets built different for different input uses.
I, for one, regularly embrace our new robot overlords, as I am the guy fixing the robots...

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Jadewombat
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Re: Ignition coil voltage issue

Post by Jadewombat » Sat Apr 30, 2016 9:40 am

I do have spark. I heard the same thing about the ignition coils, but both I have read 3.5ohms between (+) and (-) terminals and the pointless ignition instructions say the minimum is 3.0ohms. I'm not really sure what changed earlier in the week. I cleaned off the plugs, but will try changing them altogether. I disconnected 2 cylinders while cranking and it still was reading 6-9V. Gonna try the workaround of the VR sensor next.

Many moons ago I accidentally hooked up a pointless ignition up backwards at the coil and found out it only takes a few seconds to lighten your wallet of another $50 to have to buy a new one. :oops:

How would I test/change the $2 opto?

Ol'fogasaurus
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Re: Ignition coil voltage issue

Post by Ol'fogasaurus » Sat Apr 30, 2016 10:46 am

You comment about taking two cylinders off line then getting a higher reading is interesting. If you are getting that much of a cranking draw I would look into that also. There has to be some draw but is it truly excessive draw that is part of the equation ....

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Jadewombat
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Re: Ignition coil voltage issue

Post by Jadewombat » Sat Apr 30, 2016 3:00 pm

There wasn't any change in the voltage jumping when I disconnected the 2 cylinders, I was just guessing to see if they were what is drawing the voltage down.

I did a side experiment to check the opto which I'm fairly certain is still good. I hooked up the old distributor (loose--as in not mounted in the case) so I could spin it by hand and watch the spark. Even with my erratic spinning the ECU came to life. I can't explain it, but I don't trust it anyway if the MS is that sensitive to voltage or pulses for input, then I don't want to be dependent upon it driving around the block much less getting stranded somewhere further away.

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