Possible coil malfunction

[grannyknot]

Have been trying to get the Z started the last few weeks with no luck. It was running like a top last fall before I put it to bed, the only things I've changed over the winter that might effect the ignition system is that a 140 amp alternator was swapped in and new MSD plug wires - DSI Spark Plug Wires | | Datsun Spirit, Inc.

were added. I have checked and rechecked all the usual suspects then I set up my remote starter so I could crank the engine and watch the actual spark from the plugs as they are pulled and grounded against the head. The first 2 sparks are big and fat, after that they peter off to a very tiny spark as I continue to crank.

That sounds like the coil to me, but it only has 4 months use on it from new! It's a Pertronx Flamethrower 3ohm.

Battery is fully charged, gas tank was topped up in Oct. and stabilizer added, 4month old plugs were pulled and soda blasted to clean them up, air filters have been removed for start up.

Thanks,

Chris

Edited April 2, 2014 by grannyknot

[SteveJ]

From that description, I doubt it's the coil. There are no moving parts, so it wouldn't decline in performance like that. Check the resistance from the positive to negative terminals. Then check the resistance from the high side of the coil to the negative terminal. The low side should be around 3 to 4 ohms, and the high side should be over 9,000 ohms.

[grannyknot]

High side and low side? Pos and neg I understand, are you refering to the centre post terminal of the coil?

[SteveJ]

Yes, that is the high voltage or high side of the coil.

[Zed Head]

Are you running points or Pertronix ignition?

[grannyknot]

Zed, running Pertronix ignition.

Steve, using the 200ohm scale resistance between pos and neg is 3.3 ohms,

Using the 20K ohm scale resistance between the centre post and neg is 9.4,

With the power on I get 9vdc between pos and neg and 8.8vdc between the centre post and neg.

[SteveJ]

It's a good coil as far as resistance goes. Unless there is something wrong with the windings on the high side, I would look at the ignition system or the battery. See if you have a significant drop in voltage at the battery as you crank. There is a chance that the coil can't build its field up fast enough, but I doubt that.

As far as the voltage readings, static voltage readings are meaningless on a coil in a DC system. The voltage is lower on the high side because of the resistance of the wire in the coil. DO NOT measure the voltage on the high side of the coil while the engine is starting or running. The voltage is too high and will arc out of your leads.

[Zed Head]

I had a GM HEI module that started generating tiny weak sparks that wouldn't start the engine after I forgot to put two spark plug wires on before starting, after doing some work. It was hard to decide it was bad because the spark was there, just weak, but I had a spare module and know that electronics don't like stray electricity. Installed the new module, no other changes, and was back in business.

You can test the coil using a jumper wire on the negative terminal. Set the main coil wire up at a good spark distance. Connect a wire to the coil negative, turn the key on, then tap and remove the wire to ground quickly. Each tap should generate a strong spark. You'll be mimicking what the module does.

Odd aside - when you add "ing" to mimic, you also add a "k". Weird.

[grannyknot]

Zed, just did the your test, ignition pwr on, jumper from the neg side of coil tapped quickly against an exposed terminal from the centre post of coil - no spark of any kind. Same test again with the neg jumper coming from the body ground - no spark.

There is 9vdc there, how can no spark happen?

[Zed Head]

Did you leave a comma and a word out? "tapped quickly against an exposed terminal from the centre post of coil"

You want the center terminal to be close to ground so that it can spark. About a spark plug gap's width away. You could also put an old spark plug in the center wire and place it's electrode to ground. That's where the spark will happen. Then tap the jumper from negative directly to ground, away from where your center terminal is set up. You'll get a small spark from the negative jumper and a bigger one from the center terminal.

The next step, or it could be the first, would be to disconnect the negative side of the coil from the ignition system. Have only the jumper wire connected, then do the tapping. If your ignition module is shorted out, it won't let the coil circuit be broken, so there won't be a spark.

I have to warn though, that damage could happen when messing with sparks and electricity. I don't want to take you down a bad path, where you fry your ignition module while testing it.

Thinking about your problem, I remembered the Pertronix module can be damaged if the key is left On without the engine running. It may be what happened to yours, and it could happen while you're testing. I would stop and reconsider. The things that I do may not be suitable for general consumption.

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

Here's another link from Summit racing. It's for the Ignitor II but it mentions look for signs of overheating on the module.

http://static.summitracing.com/global/images/instructions/pnx%20ignitor%20ii%20tests.pdf

Edited April 4, 2014 by Zed Head

[grannyknot]

I think the Pertronix module is fried, I tried your test above using a spark plug in the centre wire and there is no spark

also, with the Pertronix module hooked up to the coil I only have 11vdc between the coil + and true ground but if I disconnect Pertronix neg wire I get full 13vdc between coil + and true ground.

I have this lovely new 123Ignition distributor here ready to be installed so I thought I would get the engine running nicely just like last fall then change over to the new distributor/ignition module and minimize any possible screwups.

Well I guess I'll just jump into the deep end and find out what happens.

Thanks,

Chris

[grannyknot]

Well, the water is fine here in the deep end, the engine is running well now, thanks guys.

Chris