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No spark problem #319302442
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Author:  ZacharyB [ Wed Nov 23, 2005 1:52 pm ]
Post subject:  No spark problem #319302442
1973 225ci Electronic Igntion

One day the car was running fine and the next, it doesn't run at all. Just cranks a lot. My first thought was the ballast resistor. "Two post or four post?" The parts counter guy asked, and I plunked my old one on the counter. He gives me a four post. So I replace it but still nothing. Got a new coil too just to see if that was it (the old one had a dent in it also).

Still cranking with nothing... Then after figuring out I had the connection on the coil backwards I saw a ray of hope that was quickly occluded with more inaction. Here are some voltage readings that indicate there is some abnormal stuff going on:

Image

Anyone have any ideas? Do I have the pos and neg to the coil backwards again? Any testing ideas? I know this 12V car won't run with only 6V at the coil.

Are there any other testing procedures I should attempt? With the ignition on I can touch the ignition positive and negative wires together and get small sparks. But I can't get anything coming out of the coil.

The black coil wire with the yellow tracer is ground, right?
Author:  valiant effort [ Wed Nov 23, 2005 2:09 pm ]
Post subject:  spark
did you check the electronic ignition module?
Author:  ZacharyB [ Wed Nov 23, 2005 5:03 pm ]
Post subject: 
I wanted to, but my Hanes says it is too complex to test for a layman like me. You're talking about the transistor module on the driver's side fender, right?
Author:  valiant effort [ Wed Nov 23, 2005 7:22 pm ]
Post subject:  spark
yep..mine wne tbad..coudnt check it so i just replaced it..figured if that wasnt it at least i would have a spare..it was the trouble
Author:  CStryker [ Wed Nov 23, 2005 8:07 pm ]
Post subject: 
Many reputable parts stores have machines to test ignition modules. They should be able to test it for you. I always like to try avoiding the "shotgun" approach of just throwing on parts until something makes it work. It costs more, and you learn less.
Author:  kesteb [ Sun Nov 27, 2005 2:47 pm ]
Post subject: 
Check the ground on the ignition module. If the box is not grounded properly you will not get any spark. A common problem with old cars and damp weather.
Author:  Slant6Ram [ Sun Nov 27, 2005 8:02 pm ]
Post subject:  Better tests
You arn't using a good test for voltage.

You want to ground one side of your meter and then probe for voltage at a specific point rather than measuring across random points.

Several sure tests to get you started.

One side of the balast resistor should read 12 volt or damn close to it.
The other side of the balast should read a few volts lower, but I'm not sure the exact number.
Now, here is an important one, the lower voltage side of the balast resistor should connect directly to the ignition coil, so, you guessed it, the voltages should be the same (or you've found a fault in the wiring harness)

To test the coil, disconnect the negative wire and then use a jumper wire, from the negative terminal to a ground. When you break the flow of electricity through the coil, it should throw a spark. That means, just unclip the jumper wire and see it the coil makes a spark at that instant.

If the coil test good, then you may have a bad trigger in the distributor, or a bad ignition box or bad wiring in between.

Have you checked to see if the distributor actually turns when you crank the engine? Sometimes the gear at the bottom of the distributor will break off when they get to be 30 years old. If the distributor doesn't spin, then the coil will never get triggered.

If the coil throws a spark with the
Author:  ZacharyB [ Mon Nov 28, 2005 1:24 pm ]
Post subject: 
Thanks for the info, I'll put it to use ASAP.

Just for your information, the distributor turns and even the air gap between the reluctor and the pickup coil is correct. But I'll check the ballast resistor again and the ground for the ignition module.

I just remembered I was doing the proper voltage test earlier on my ballast resistor. One side read 11.8 volts, the other side read 6.8 volts or so, what I'm getting at the coil minus resistance from 30-year-old wires.

My question is can ballast resistors be bad out of the box? When I got this ballast resistor it came in a very old-looking box, indicating it might have sat on the shelf for quite some time.

What's confusing to me is that the resistance is correct between the bottom two prongs (main ballast resistor circuit): about 1.2 ohms in 60 degree weather. The upper two prongs, the auxilliary circuit, have a resistance of 5 ohms.

I'll have to check my coil but it is brand new (even the box), so it is last on my list of suspects. But I know the car won't fire on 6 volts.

Thanks again
Author:  ZacharyB [ Wed Nov 30, 2005 1:41 pm ]
Post subject: 
It was the transistor. Thanks for your replies, everyone. Does anyone know if the transistor has any government over what kind of voltage is going to the coil, because I was wrong. The car runs on 6 volts with a 12 volt coil.

Also, this new transistor works very well but only has four prongs on its plug where the previous transistor had five. What was that last plug for? Unused for this model but used for other models? Emissions control that the company (AC Delco) knows does not apply anymore?
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