TheSamba.com :: View topic - Low voltage on positive side of coil..no start

Tue Feb 04, 2014 11:04 am

Hi All-

A bit of a problem I'm having. Just did a full rebuild on my 74's engine.
I replaced the battery, coil and all ignition components with the rebuild.
I go to start and break-in the new engine and it turns the starter but doesn't start the engine. I'm getting 12.6 volts at the battery, but only 10.5 volts at the positive side of the coil (15). Every now and then when trying to crank no lights would show up on the dash and acted like the battery was disconnected...then tried again and got dash lights but still unable to start engine.

I'm away from the car till tonight, but does this sound like an ignition switch going bad or dirty connections on 15?

Thanks

Thanks

Tue Feb 04, 2014 5:04 pm

Yes!
Check every terminal and join in the ignition circuit

Tue Feb 04, 2014 6:34 pm

Could be ignition switch, could be just dirty connections.

I've had this happen when the wire from the key to the fuse box for the coil had a bad connection.

Tue Feb 04, 2014 7:54 pm

Weird

Tue Feb 04, 2014 8:08 pm

It is gets even stranger...

I cleaned all connections and get the volts to 11.5
...not enough to start the car. So I decide to check
the volts at just the black ignition wire (disconnected
from the coil) and I got...12.5 volts! So I reconnect the
the black ignition wire to the coil and disconnect both the
choke wire and electronic ignition wire...and I get 12.5 volts.
So, I reconnect the choke wire and it drops to 12 volts...and then
reconnect the electronic ignition wire and it drops to 11.5 volts.

So...if I have the choke wire or the electronic ignition
wire (or both) connected to the coil I won't have enough volts
to start the car....I'm at a loss?!?!?!

Tue Feb 04, 2014 9:07 pm

you said you have electronic ignition install a dist with points you don't need 12 volts to start the car.

Wed Feb 05, 2014 6:01 am

Typically 9 volts should be enough to get you a spark. Are you reading the voltage while cranking the engine? It could be a lot lower while cranking than just when the ignition is on but the engine not running. Don't become too fixated on the coil voltage, your problem could easily be elsewhere. Are you getting fuel? Are you 100% sure you have the distributor drive gear is installed correctly and the wires in the right positions?

Wed Feb 05, 2014 6:28 am

It might start with points...though it drops to just 12 volts when you hook
up the choke wire...I'd like to find out why it drops so much when
hooking up these wires.

Thanks for the ideas so far...

Wed Feb 05, 2014 6:33 am

I'm checking the volts while the key is on and not cranking

Wed Feb 05, 2014 6:44 am

That's a sizable voltage drop.
Something else to consider is that (in stock form) the terminal 30 circuit that powers the ignition switch is not fused. Neither is the terminal 15 circuit that powers the coil, choke and idle solenoid.
Check this wiring diagram:
http://www.thesamba.com/vw/archives/info/wiring/181_Wiring_Diagram_4-73.pdf

If you have 12.6 volts at the battery +, follow the current path to find the voltage drop. Check the voltage at both terminal 30 connections of the headlight switch. Next, check the voltage at both terminal 30 connections at the bridged supply side of the fuse panel. Then check the voltage at terminal 30 of the ignition switch, switch on the ignition and check the voltage at terminal 15 of the ignition switch. A shorted fuel gauge, sender, or warning lights can cause a voltage drop at terminal 15; remember, that circuit is not fused. Lots of people add a fuse to that circuit, but that's a different subject. If you get 12.5 volts at the coil terminal 15 with the choke disconnected, check the ohms across the choke element; maybe it's shorted. Same thing with the idle solenoid.
Well, you get the idea; just follow the wiring diagram and stick with it until you find the problem.
Good luck, Mondshine

Wed Feb 05, 2014 8:09 am

I'll check the ohms at the choke element and idle solenoid...I am getting 12.5 on the 15 terminal at the coil...

Wed Feb 05, 2014 8:27 am

Just FYI, I pulled a couple parts from my "junk box" and measured 1.5Kohms across a choke element, 33ohms across a solenoid. I don't think I've ever seen a specification for these things, maybe somebody else will chime in with their readings.

If a minor short exists in this circuit, you would never know, unless the black terminal 15 wire melts, but that's the way these cars came from the factory.
That's why it's not a bad idea to fuse the ignition circuit.

Good luck, Mondshine

Wed Feb 05, 2014 8:35 am

Thanks Mondshine-

Now I have numbers to compare to. I did notice the choke
element had a larger drop of voltage compared to the solenoid.

Thu Feb 06, 2014 9:56 am

So, Measured the the choke element and got 1.7k ohms and 30ohms
for the solenoid.

Switched out the electronic ignition for a condensor and points...had the
same voltage drop as the electronic ignition (.5 volts). But was able
to start the engine and do a proper break-in. I'd really like to run the points replacement (electronic ignition) on this engine.

Does the points replacment (electric ignition) really take more volts to
get the car started than good ole' points? From what I just dealt with it seems that way...or the electronic was crap right out of the box (compufire). Still I was getting a healty drop of volts from the solenoid, choke element and electronic ignition...

Thanks for all the help...

Thu Feb 06, 2014 10:19 am

Are you sure you have the wires to the module hooked up correctly?

You could add an ignition relay and have close to battery voltage at the coil if you wanted.

Thu Feb 06, 2014 1:24 pm

glad you got it started by changing to points. I don't no if the electronic is better but I have noticed that almost everyone that runs the electronic system keeps a dist with points as a extra. Not saying the points or better but the Domeck Brothers only use dist with points in any thing that we build or own.

Fri Feb 07, 2014 12:15 pm

Wildthings wrote: Are you sure you have the wires to the module hooked up correctly?

You could add an ignition relay and have close to battery voltage at the coil if you wanted.

I'm pretty sure I had it hooked up correctly. I've added a relay to help with
the starter to engage on a 58' single cab a long while ago...but have never wired one up to the ignition...sounds like a great idea. I have one dumb
question though....how would I wire it in with the iginition...?

Thanks again

Fri Feb 07, 2014 12:37 pm

The ignition would just provide the trigger for the relay. You would power the relay from the 12+ lug(#30, B+) on the starter solenoid, or from the B+ circuit on the voltage regulator.

Fri Feb 07, 2014 2:01 pm

So I would wire this relay almost the same as a hard start relay..?

Thanks

Fri Feb 07, 2014 2:19 pm

Turd Furgusson wrote: So I would wire this relay almost the same as a hard start relay..?

Thanks

Yes, but you would be using the #15 ignition circuit as the trigger verses the #50 starter circuit as per the hot start relay.