240 General: Won't idle on cold start - LPG - Carburetor

[Harvey Birdman]

Hi Marc... How and what bypasses the ballast resisitor. I traced the wiring from either side of the resistor back to the ignition control unit... I wish I had a circuit for that.
I can't see how a 0.3 volt drop in battery voltage would cause the coil voltage to drop to 7.2 volts. I'll charge the battery tomorrow but I don't think that is the problem.

I am getting the same voltage (7.2v) from the ballast resitor to ground as I'm getting from terminal 15 on the coil to ground. I'd love to know where I'm losing the 4 volts.

[marcmarel]

The easypeasy way to do this would be draw a straight line between A: the battery + and B: terminal 15 on the coil.

[Harvey Birdman]

Originally Posted by marcmarel

Your ballast resistor is doing it's job. When the engine is running it limits the voltage on the coil (it's rated 9V), when starting it is bypassed so the coil gets all the available volts and makes nice big sparks.
Voltage on the battery might be a bit low, maybe that's why the sparks are orange. Should be 12.6 V.

The ballast resistor should produce 10.8-11.2 V, same voltage should be present at 15 on the coil.

Hi Marc

Here's the latest

I've checked all the earth connections and the all seem solid.

Cleaned all connectors.

Purchased a 2nd hand Ignition Control Unit and substituted for the original and basically got the same results. So I either have 2 faulty ICU's or the problem is elsewhere.

Please see attached ignition diagram... I've added in the voltages I measured with the ignition on.



I noticed that after a few minutes the coil gets warm and the ballast resistor gets very hot. By my calculation there is about 2.7 amps running thru it. Now the manual specifies a 0.9 ohm resistor for the breakerless system but the car has been running without fault for 2 years with this 1.45 ohm resistor.

I've been told these Bosch Ignition Control Units are very reliable. I've attached some pics of the inside of the 2 units. There is a slight difference between them... 2 components less on the later revision. Diode D11 and Resistor R21, lower right hand corner.



I've done basic checks on the components in both units, everything appears to be OK but without a schematic it's a bit hard.

Would anyone on the forum have access to a schematic or service data for this ignition unit. Bosch: 0 227 100 018

If I had a circuit with some nominated test points and voltages I could at least verify the unit is working.

To rule out the ignition switch, is there a way of hot wiring it to just test the basic components?

I've got a feeling this is something simple but at the moment I just can't see it.

Looking forward to your reply.

Thanks again

[Harvey Birdman]

Hi again

Images aren't posting so here's the links.

http://www.glowfoto.com/static_image.../img5/glowfoto

http://www.glowfoto.com/static_image.../img4/glowfoto

http://www.glowfoto.com/static_image.../img6/glowfoto

http://www.glowfoto.com/static_image.../img6/glowfoto

Thanks

[marcmarel]

I have no idea about this ICU, probably some very solid components in there.

Your resistor resistance is almost double what it should be, why not bypass that with a simple wire and install a 12 V coil.

[Harvey Birdman]

Originally Posted by marcmarel

I have no idea about this ICU, probably some very solid components in there.

Your resistor resistance is almost double what it should be, why not bypass that with a simple wire and install a 12 V coil.

I have a feeling it maybe there to protect the ignition control unit.

I thought the coil was a 12 volt coil.

[marcmarel]

The resistor is there for the coil, which should be a 9 or other lower voltage thingy. A resistor on a 12V coil could well be the source of your orange sparks, since the coil isn't getting the voltage it needed.