TheSamba.com :: View topic - Low voltage at coil in run position 75 Westy

Fri May 04, 2012 5:39 pm

OK, My 75 Westy is pissed at me because I haven't driven her in a few months due to back surgery. It will crank but won't start and when checking for spark, there was none except for one spark when the cranking stops. I have 13 volts at the battery but only 9 volts at the coil when ignition is in the run position. I have all stock FI and everything else is stock except for a pertronix. Any thoughts on where to start?

Fri May 04, 2012 5:53 pm

Could be a bad wire or connection in the power supply or it could be an extra load of some sort near to the coil.

You need to work backwards through the system. What is the voltage you get with the big feed wire (red/wht?) comes into the fuse box?

Fri May 04, 2012 7:21 pm

we just went thru this with someone else about 20 - 30 days ago. Read this:

http://www.thesamba.com/vw/forum/viewtopic.php?t=504441&highlight=coil

Sat May 05, 2012 12:35 pm

OK, went to the coil and checked the 12v wire feeding it and it's ok reading 12+. Then I reconnected it and started looking for where it was draining. I found I gained around 1/2 volt when I disconnected the red wire going to the pertronix. However, I had over a two volt gain when I disconnected the fuel pump (the PO wired it directly to the coil bypassing the double relay so it always ran when ignition was in run. I know, I know). When I checked it it was not running but it was hot. Do I have a bad pump? Any thoughts on the hot wire to the pertronix?
Thanks!

Sat May 05, 2012 1:03 pm

probably yes to both questions. A 2V drop when you attach the ignition module means either you have a bad connection or ignition switch, or it is consuming lots of power. The whole idea of a relay for the fuel pump was to avoid that current it draws from having to go thru the ignition switch. Personally I would take the time to rewire things back to stock since we know stock works.

Sat May 05, 2012 2:51 pm

I have a 1971 Type 2 - with a older Type 1 engine that uses a mechanical pump.

I've added a relay circuit just for the ignition coil, back-up lights, carburetor idle shut-off and choke element.

This way the current doesn't have to start out from the back of the Bus, pass through the ignition switch up front and then return back to the engine compartment.

By-passing the relay on your 1975 with an electric pump and drawing current through the switch, will eventually lead to failure of the ignition switch, in addition to fhe voltage drop you are measuring when the pump is running.

- Andrew in Austin, TX -

Sat May 05, 2012 3:13 pm

Thanks for your help - I have confirmed that my fuel pump was shot and when I disconnected it, my voltage at the coil went from 9.5 to 11.5. I have only 2 wires going to my pertronix unit, a black one that runs to the - terminal of the coil and a red one that goes to the + terminal. When I disconnect either one of these individually, the voltage at the coil goes to 12.5 (a 1v gain). Is this typical?

Sat May 05, 2012 6:08 pm

Never checked the amp draw of a Pertronix Unit, but having a voltage drop of 1V sounds reasonable, especially with the age of the wiring of these things.

Sat May 19, 2012 8:13 pm

Thanks for the feedback and advice everybody. I just got my new Bosch electric fuel pump in the mail, installed it and the bus started with no problems. I took some time to ad a relay and clean up some wiring and everything is humming. Again, thanks to all air cooled friends.

Sat May 19, 2012 8:19 pm

Oh yea, I confirmed that the burned out fuel pump was drawing so much voltage that there was no spark - when troubleshooting, I always started with the 3 (fuel, ignition or compression). I wasn't expecting one of them to cause the other.