The Stovebolt Site Forums The Shop Area Engine Shop 1968 / 396

Hello everyone, thanks for letting me join !
Usually pretty good at these things but am stumped on this issue.

No spark to plugs. Simple I thought.
Was time to refresh anyway, so new points, condenser, rotor and cap.
No spark. Turns over, power to the primary side, and spark at the points.
New coil. No luck.

AS usual, ran fine the last time I used it. But after sitting for a few months it is being stubborn.
I am to the point of thinking it is grounding out at the distributor. Maybe??

appreciate any direction you all can give on this one.

Larry.

Plug wires or grounding the points. Have you tried putting the old rotor and cap back on it? I have seen both parts bad from the new box.

No spark to plugs? What about the center lead on the dizzy?

Can you get a spark from it?

New condenser bad maybe????

Actually have tried 3 different condenser, had one in the garage from another set of points.

That probably isn't the problem , then but it eventually will be. When you get your engine straightened out, contact Jon G on this site. He produces lifetime 200,000hr condensers. The new ones you buy are usually junk right from the box.

How do you know the plugs aren't firing? What tests did you perform?

So this is on the 68 396 ? Easy fix use an HEI distributor. Just need one wire to it from the ignition switch.

I did try the old ones but no luck.

I have tested the plug wires with a multi meter. tested 2 from each side of the engine. No luck. This weekend I am going to use PDF from the elc. page "No Spark on Your Stovebolt" and go through those steps and see what the test light shows. If that checks out, there was also a post in the elc. forum from Bill Hanlon that had some other tests to check. With the age of the truck I am leaning towards the coil wire coming out of the distributor. Not sure how much chafe protection is at that point. Will update Saturday afternoon.

I went through the Tech Tips for no spark on your Stovebolt.
Both small terminals at the coil are lighting up the probe with the key on, with the points open and when closed. So I am reading I have an open circuit between the coil and the distributor.
Any usual areas this might be happening at?

On a side note, I installed a new starter. There isn't a way I could of wired it in wrong unlikely as that sounds.. The motor turns over and has power to the coil..
At this point I am questioning everything.. ugh...

Check the wire inside the distributor housing from the housing to the points. It's being flexed constantly by the vacuum advance and the wire strands under the insulation can break, creating an open circuit. Disconnect the wire at the points and pull on it- - - - -if the insulation stretches, the wires inside are broken.
Jerry

You are correct that the negative side of the coil shouldn't 'light up' when the points are closed.

Leave the key on and points closed.

Pull the distributor cap and touch movable arm of the points. If no light, the wire from coil - to the movable arm is bad. If light touch the light to the fixed part of the points.

If still light, the points are not grounded. If no light the points are bad.

Check the continuity of the wire from the coil to the points.

new points were not closing all the way. adjusted. now when points are closed, no power to neg side of the coil. When open, test light lights up. We have constant power to pos side of coil. I am going to put a volt meter on the pos side of the coil to verify the correct amount of volts, and also test while turning over the motor.

Will also do a better inspection of the wire at the distributor where it comes in from the coil. Although it seems to be working now, there is not much play in the wire when connected to the coil.

At this stage I am going to rule out the ign switch and the wiring at the starter. I have a firewall mounted ballast for the coil. Has that ever caused anyone any issues?

thanks for everyone's help, this one really has me pulling my hair out....!

With the points closed, the negative side of the coil is grounded. It's impossible to have enough power to light up a test light at a "ground" connection. (Unless somebody repealed Ohm's Law!)
Jerry

Jumper across the ballast resistor and see if it fires. If it does replace the resistor.

Hello.
I removed the ign. wire from the coil and used a jumper from the battery to the coil.
No spark still to the plugs. I'll unhook the condenser and try again, but...

Look for the hole burned in the middle of the distributor rotor that's shunting the spark to ground. It's a common failure that I've been seeing since the late 1950s.
Jerry

Hi Jerry.
I checked out the rotor, but all looks OK.. I finally hooked a volt meter up to things. I am getting 14v to the negative side of the coil with points open and - zero when closed. Getting a little less on the the positive side of the coil, not sure why. ?
The large issue is the 6 volts I am getting out of the coil.
Keep in mind it is a new coil. Why would the coil not be building up enough juice? Have other thoughts , but trying to keep the thread to one question at a time so I can eliminate and move on...

If you're measuring the output voltage of the secondary with the coil primary energized, you won't get the high voltage that fires the spark plugs. That only happens when the coil primary windings are de-energized (points open) making the magnetic field collapse quickly and inducing the high voltage spike in the secondary. And it only lasts less than a second. It's possible that the secondary windings are open circuit.

Kevin,
wouldn't I see the needle on the test meter jump when connected to the coil while turning over the motor?

Someone also brought ignition relay as a possible issue. I am familiar with the battery relay but for some reason I though that had to do with charging the battery.

Yes, you should see a jump in the test meter if the points are opening and closing with the engine turning over. That's why I mentioned the secondary windings being open circuit. You did say the coil is new, but replacement parts being bad out of the box is not unheard of nowadays.

I can ohm the coil and see what I get from that, as far as that being an issue. I am also a little unsure why there is only one wire to the + side of the coil. I thought there were 2 one for starting and the one for running supplying lower voltage. However when I looked at the starting diagram in the manual, it showed 2 wires connecting before the coil, one from the batter and one from the ignition and only one to the coil itself. That seems a little counterintuitive? While cranking the coil ought to spike the test meter pretty hard if it is putting out the suggested voltage, not just wiggle at the 6 volts it seems to be getting from the + side of the coil. I don't think the coil is building up any voltage to release when the points close.. And I have no idea why that would be. sucks getting old, I am sure this would of been a no brainier 10 years age. lol

It sounds like you’re measuring on the primary coil terminal and expecting to see high voltage that goes to the spark plugs. The high voltage should be measured on the center where the coil to distributor plugs in. And the high voltage should happen when the points open after they’ve been closed for a bit.

Well that was 3 months of Saturday fun! LOL
Truck is running now. I used to tell people I kept the truck because I could work on it still as it was just points. ha ha.

Here is what I can figure out.. The coil was bad. But I replaced that after the points and condenser... I think I got a bum condenser or to was not seated all the way in the clamp. I switched it out to a blue streak on I had laying around and got some week spark finally. But I was testing right from the coil w/o the condenser. I read that the condenser plays a role in the size of the spark. So in the end, I re gaped the points and took a plug wire right off the top of the coil and turned over the motor and got a satisfactory looking spark.

I choked the carb and it started right up. After a year and a half. !

I will also mention that years back when I bought a new coil, the parts counter guy told me I needed a ballast. So I installed one.
Going through all this nonsense and looking in the 68 rebuild manual, Chevy has an inline ballast for that motor model year and an external one is not needed.
There was only one wire going to the + side of my coil. So I was starting with the reduced voltage, not the full 14 volts from the battery.
Also might cause a weaker looking spark.

But hey... Thanks for all your help slow walking through all this!! I look forward to a brake issue or a wheel bearing I can fix that are not electrical.!!

Late 1960s and early 70s GM vehicles with point-type distributors use a nickel/chrome resistance wire from the ignition switch to the coil to drop the voltage to the coil primary winding, instead of a ceramic resistor. The wire is about 10 feet long, and actually doubles over on itself inside the harness. It also is stiff, silvery-colored, not copper, only has a few strands, and has woven fiberglass insulation. I guess the GM engineers thought it was an "improvement"!
Jerry