No spark on hot days

[Xenn]

Fuel pressure is fine, sprayed starter fluid as well and nothing, however, still getting no spark with the timing light.

Now the weirdness, when i hook a voltmeter up to my ignition coil i get +12 volts out of both the positive and negitive terminals, and sometimes my positive terminal will seem to "cycle" from 0 volts back up to 12 then 0 again, i can understand my ignition coil being shot , but i dont know why i would burn through my second one in a few months, the last one was old and i expected to need to replace it, this one much less so.

[Xenn]

Zed head i said in op that both my alternator and distributor were 280zx swaps

[Zed Head]

Ignition coil is new, distributor and alternator are both new upgrades/swap (new 280zx parts wired in)

I saw a list of parts and a statement that new ZX parts were wired in. Not clear that all of the parts are ZX, and grammatically it is undefined! Could be just a ZX alternator and coil, which still gives plural ZX parts.

Bonus - The terminals of module are wired to the negative and positive terminals of the coil. The negative and positive terminals of the coil both have battery power when the key is on. Therefore, the terminals of the module will have battery power when the key is on. Logic, gotta love it!

Good luck with it.

[Xenn]

Above all else, and bar none the weirdest thing thst happened, hooked a direct line from the battery positive to my coil positive (which also kicks in my accessory) then hooked a linefrom my batt negitive to my coil negitive, it sparked once, then not again, disconnected the wires, hopped in my car anf it started without a problem, even still had a sparkplug off, i guess at this point my question is what could cause my ignition coil to behave that way, that being having positive voltage out of both terminals until i forced the current to go the right way?

[Zed Head]

Sounds like you just jiggled a bad connection.

You're not understanding how the coil works. Without current flow you'll see the same potential (voltage) on both terminals. You didn't force current to flow anywhere.

[Captain_Zeros]

Ok so, how were you measuring voltage at the coil? The coil is just that, coils of wire, the "plus" and the "minus" terminals are attached together inside the coil so if you're trying to measure it in-situ in the car, both are going to have power because the power is flowing through the coil through the meter to ground and that will show up as voltage. When your volt-meter isn't provided a path to ground current won't flow (if the ignition module is operating properly) unless the distributor's reluctor wheel is the right place to fire off the coil.

Also, shorting the negative coil to chassis ground is generally not a very good idea. Automotive coils are designed to pulse very short periods to ground through either the points or through the electronic ignition module then off again, leaving a coil shorted to ground can overheat it and cause it to fail prematurely.

Edit: how you really want to test the coil is by removing it from the car and measuring the resistance between the terminals as specified in the factory service manual to see if it's internally shorted out or not. Also go ahead and clean up and snug down all your connections in the area.

It's possible your ignition module is going bad and that's causing a failure to spark, but unless you have a spare known-good one to swap in I'd go ahead and check everything else first.

Edited June 19, 2013 by Captain_Zeros

[Xenn]

Sorry zed head for the late reply to your question, I was checking this site and posting via my phone, and it didn't like to update others posts. Also yes, grammar is key, and I can fail miserably at it at times (remember, put your kids through private school, public school is just a business nowadays) ANYWAY thank you for the ignition module answer, as well as the ignition coil voltage answer.

It made no sense to me as to why it would work with me doing that either from an electrical standpoint, or a logical one, it was a hunch I acted on, I didn't short it to the chassis, I connected the + coil to the + bat, and the - coil to the - bat, it sparked once, then wouldn't spark again, simple alligator clip connections not held for more than a second, that is the absolutely only thing I did to it that time (check one thing, see if it will start, check another, see if it will start, one at a time, no more) and it fired up without a problem, with those wires disconnected, even with a spark-plug wire still off so I could listen for spark.

As for checking the voltage, I just took a voltmeter put the negative to a ground, and touched the positive to one terminal then the other, I was worried the voltage on the negative terminal was 12 because I assumed that since it was the negative post, and the chassis is basically a negative ground to the battery, the voltage potential between the two would be 0 since I assumed the negative post post simply grounded out seems I was wrong, but I come here to learn, a basic circuit knowledge only helps you so much on a system as complex as a car.

[Captain_Zeros]

Battery minus is the same ground as chassis ground, coil minus is not as you've found out. That's why they call it learning! A second or so of shorting on the coil probably won't kill it, but I'd go ahead and check the resistance if your meter can check ohms because it's easy to do and will give you one more piece of information.

Testing Your Ignition Coil - Coil Resistance Test - How To Test Your Ignition Coil With an Ohmeter

My 240Z has a ZX dizzy/coil/alternator in it too, so I have a grasp of how those bits work, but my car doesn't have an ECU so I haven't bothered to learn about 280z factory ignition :stupid:

I have a thought in the back of my head, you said "distributor and alternator are both new upgrades/swap (new 280zx parts wired in)", did this problem start before or after you put in the new parts? Are they new manufactured parts or are they used parts?

[Xenn]

Alternator is new, dizzy is remanufactured, think i might pick up a new ignition module to be safe. The problem started about a month after i rebuilt the top end, or 2-3 months after i replaced the dizzy, 6 after alternator. It didnt start until it got hot out.