The Stovebolt Site Forums The Shop Area The Electrical Bay 6v ignition system - no spark from coil

Trying to get my '51 GMC 100 running for the first time after buying it. Previous owner said it ran good and he drove it around town prior to parking it. That was about four years ago. I have a new 6v battery, the starter cranks over fine and I get 6v or so on both leads on the coil. The points, condenser, cap, rotor and plugs are nearly new. The coil does not look new. While cranking there is no spark from the secondary output from the coil and all I know past that is that the points are opening and closing. I'm going to do an ohms test tonight on the coil but is there something else I should be checking?

Thanks for any help,
Dan

The coil voltage should not be a steady 6 volts as you crank the engine. It should pluse as the points open and close.

Okay, that's what I thought. I'll test that tonight. If I get a pulse I guess I'll buy a coil.

Clean and gap your points.🛠

Distributor cap grounded ?

How does this happen? The only thing touching the cap is the center high voltage wire and the metal spring clamps. I've never seen anything else attached to a cap before.

I searched "grounding a distributor" and a lot of guys talked about having trouble with spark until they grounded the dist. Most just add a wire between the condenser screw and the block. Is this what you're referring to?

Another way to ground a distributor is to run a wire from a distributor-cap clip screw to a screw on the bracket holding the coil to the head.

Below is a test process that Chipper posted on the VCCA site posted (6 volt electrical test process).

Hope this helps. Cheers, Dean
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You can check most of the ignition system before trying to start the engine. Connect positive post on battery to positive post on coil. Or you can turn on the ignition switch then remove the wire from the positive post of the coil. Quickly pass the terminal end of the wire past a ground to see if you get a spark. Or if you have a VOM or test light you can test the positive post on the coil with everything attached and a piece of paper between the points. You should get battery voltage or light the test light if the wire, ignition switch and battery are good. If no spark or voltage then check the switch, wires or battery. Once you have power to the positive post on the coil then you can test other components.

With the paper between points (or points open) you should have battery voltage on both coil posts and to the hot side of the points. If not check wires and terminal ends.

Once you have voltage to the points short across the points with a screwdriver. You should see and hear a spark. With spark at points, hold the end of the center coil wire approx. 1/2" from ground and short across the points. You should get a spark from the end of the wire to ground that makes a "Snap". If not check the condenser to see if it is attached to the negative post on the coil or wire to the points on the distributor and the case is grounded. If not spark or weak spark replace the condenser. Once you have a strong "snappy" spark from the coil center wire, test the points. Remove the paper from the points and open and close then by hand. If you get the same strength spark as shorting across them they are good. If a weaker spark, clean or replace the points. Once you have a good strong spark from the center wire operating the points, put on the rotor, distributor cap and center coil wire to the distributor cap. You are ready to start the car.

As you can see it does not take a second person to test and diagnose the ignition system with a set of points. Don't have to turn over the engine either.

If there is a problem with the engine starting or you have any doubts that spark is getting to the plugs it may take a person to hit the starter while another person holds a spark plug wire 1/2" from a ground. It can be done by a single person on a '29 to mid-30s Chevy by activating the starter switch with the left hand and holding the wire with the right. If your left hand is weak it also can be done by switching your hands.

A condenser (capacitor) has two ends, both of which need to be connected. The outer metal housing of the condenser is one end and need a path to ground, or at chassis common. They usually fail in the shorted state (electrolytic), I have temporarily removed them from the ignition circuit and car will start and run. Not long term as they are there for a reason.
If you don’t know what the ohm meter test on the coil should/should not revel...ask here.
+1 for “Justhorsenaround’s” idea.

Make sure the points are "opening" and "closing" as the distributor goes rounds as you turn the engine by hand. If they dont FULLY open and then COMPLETELY close it will not run. I dont know all the terms but I think its the "dwell" or duration they stay closed or open. Like I said make sure they are doing that.
You can even put a test meter on the wire that goes to the distributor and it should get V+ on and off as the distributor spins.

I had this problem and it was just barely out of adjustment by fraction of a hair. It drove me crazy for a whole afternoon till I figured it out. I guess someone more familiar with breaker point ignition troubleshooting would not have that probglem.

Hope that helps

So much good information here, thanks to all of you. I'll have time again tomorrow to do some checking. One of the first things that caught my eye was that the points looked like they were opening too much. I didn't have my gauge to check but I'll have it tomorrow.

Latest update: I went through the test instructions that were posted and got to the step where I short the points and look for a spark between the coil center wire and ground. Nothing. Says it might be the condenser so I got one, changed it, and no spark. I pulled the power wire off of the dist from the coil and touched ground while holding the center coil wire near ground and at first got nothing, then I was able to get a random weak spark, like not very visible spark. So, after reading through your comments again I'll try removing the condenser to see if it's shorted somewhere but I'm kinda running out of ideas. I do plan on cleaning every ground that I can find for the ignition system and engine. Oh yeah, I also checked the point gap and it was really close, slightly large, but adjusted it anyway.

Try this- - - -with the engine not running (shouldn't be a problem, right?) turn the ignition switch to the "on" position and tap the starter until you see the points close. Measure the voltage at the coil (+) terminal to a good ground like the engine block, etc. It should be very close to the voltage measured directly at the battery posts. Then measure voltage from the (-) terminal or the terminal at the side of the distributor to ground. It should be very near zero. If you get a voltage reading at the distributor with the points closed, CLEAN THE POINTS! Burned or high resistance points were the cause of at least half the "cranks but won't start" complaints I've fixed in the past 50-something years.
Jerry

The first question is what did the motor do when you first tried to start. No fire, popping, fast spin, slow spin, backfire..........?
What does the motor do now? Please answer those questions carefully.

I hope you are trying to start the motor, at certain "new part/new adjustment" intervals, to see any change in behavior. If you hear a fire it gives you a clue.

I don't know if you are using some testing equipment or eyeballing the spark.
These visual spark tests are always advised for troubleshooting. The spark is VERY hard to see, and VERY hard to get strong enough to see, due to the operator not getting good contact, the contact surface is not adequate, motor vibration and the ambient area lighting is too bright. You can run in circles as you are doing. I hate to suggest the "replace parts" method because you are supposed to "test and identify". That is easier said than done for most folks. Now-a-days, the bad news is new parts are bad out of the box. Especially condensers. The good news is the stuff is relatively cheap. Get new ignition parts, triple check the points gap. I can't tell if you bought all new parts or were told they were new. Which is it? Ignition parts ARE NOT reliable after sitting for 4 years. You need points, plugs, plug wires, condenser, dizzy cap and rotor, coil. Good battery, good ignition switch. You are testing yourself into oblivion. If parts are new and timing is right and points are set, it will start. Be sure you squirt some gas down carb so that you are not fooled into thinking spark when it's gas. You have convinced yourself and everyone but me that it's spark. I never heard you say you took a plug out in the dark to see if it fires when cranking. Start at the plug gap and work back. You can't do any of this spark testing in the sunlight or shop light. You can't see a weak spark unless it's dark. You need to see any spark.

You know this truck is POSITIVE GROUND right? I do not know what electrical tests you have done or whether they are affected by that or not. Probably not.

Okay, I think you're right, it's time to start from scratch and set everything to "factory" spec instead of assuming what the previous owner told was correct. The story goes... the PO had the brakes done at a shop and drove the truck around town several times before parking it. He was going to restore it with his son but his son never got interested so it sat for about two or three years before I bought it. After I got it it sat for another two years (I can't believe it went that fast) and that brings me to today. The plugs, points and condenser look new, although you can tell they were used for a short while. When I try to start it it turns over at what I would consider normal speed, sounds like it has compression (I haven't checked) but never gives a hint of starting. I tried carb cleaner and gasoline in the carb at first before realizing that it wasn't getting spark.

I can rebuild engines (and a few transmissions), adjust mechanical fuel injection and tune duel carb setups on old BMW's but I haven't been able to get a simple points ignition system working on an old truck. Yeah baby! 8-/ I'll work through a checklist from the beginning...

It will be something silly and easy to fix. If you don't replace all that stuff it will be the one thing you didn't replace. It's all easy and cheap to start with a good baseline.

You know this is a positive ground system, right? GMC was NOT negative ground. Check that. May or may not affect your tests. So don't get mixed up with the test procedures posted previously.

Please Reread my post, I was typing/editing when you posted again.

Today’s aftermarket condensers are notorious for being defective.

That red wire from starter switch to ballast resistor bottom terminal is to supply full voltage to coil when cranking, it's disconnected when motor starts and then resistor voltage (less than full) runs the ignition. The red wire is on what is known as the starter switch "side terminal". If that part of the switch is bad, it is possible that the starter is taking too much voltage and leaving a weak spark during cranking. Run a direct wire from the big starter stud, provided you clean the rust off of it, to the coil and try starting the truck. This will bypass the "side terminal" on the starter switch to see if it is bad. You will need to disconnect this test wire and turn key off to stop the motor. Make sure all the other stuff you have been messing with is all hooked back up first.

You can also just run a test wire directly from the battery to the coil.

Please confirm your GMC is wired POSITIVE ground and you know that.

Yes, it is a positive ground system and I am aware of it. It's an assumption I made because the red battery cable goes to the chassis and the black cable goes to the starter. There was no battery in the truck when I bought it, but, I was looking through the photos I took of the truck when it was at the PO's house and there was a 12v battery sitting on the driver's side floorboard. I don't know if they just stored a battery there by coincidence or if they were using a 12v battery in the truck. Two of my friends that have owned these trucks in the past said it looks like a 6v system, generator, etc.

I was having a similar issue with my 54 Chevy and it turned out to be a bad Flux Capacitor (ballast resistor). Some voltage was getting through but not enough for the spark plugs to fire. I changed it out and it started right up.

Dave, if you had a ballast resistor was there a bypass wire directly from the starter side terminal to the coil? As shown in his pic.

Next I'll run the wire from the battery to the coil like you suggested. The wiring diagrams that I found don't have the ballast resistor. Did some of them come with them and some not?

I'm not an expert on this era of truck. I was surprised to see a ballast resistor in 51. They can be added to almost any truck
with points if a person wants. As you said, Chevy wiring diagram does not show a ballast res.

Let's see what your test wire does.

If someone uses a 12V battery on a 6V system, they could blow your light bulbs and other components.

It would be good to change to negative ground and 12V. Both are easy and are in the tech section. Albeit keeping it unique and stock is nice also. I guess.

A ballast resistor was not used/needed on a GM 6v system (positive or negative ground).

Thank you. Do you think someone tried using a 12v battery and did some trickery? It's one of those things that when you see someone rattle can the entire firewall, and everything mounted to it, regulator, all the wires are now black, I start thinking that other things were half-assed. Now after seeing that 12v battery in the photo I need to ignore anything I've heard from the PO.

Per Tim's post, several things come to mind. If it does not need a ballast if running 6V:
1. Maybe a ballast reduces the point volts too much. Weak spark. On 12V it reduces about 25%-30%. on 6V that would be 4-4.5V to coil/points.
2. Hooking up the test wire is even more important now if no. 1 is true. What is holding this test up?

I agree about the PO. Everything needs redone or rechecked. Don't trust any wiring.

Check to see if coil says 12V or 6V on it. Check a bulb or two. Read the tech tip and look for signs of upgrade to 12V. See if gen is 6V.

PO almost HAD to be converting to 12V to add a ballast. Considering Tim's comment on not used, not needed for 6V systems. Not a GMC thing?

not needed on GM 6v systems - Chevrolet or GMC 6v

I work about 50 hours a week at my day job and then split my personal time between working on some property and working on this truck. Fortunately, the truck is located at the property so it allows me to work on it more, although usually small chucks of time. I promise to run the test wire today and report back!

Flathead Ford V8's in the 1940's used a ballast resistor on 6 volt ignition systems. My 47 Mercury had one. There was no bypass system and sometimes the spark would get weak when cranking with a less-than-full charged battery. I've never seen a 6V GM system, positive or negative ground, with a resistor.
Jerry

Does point to a 12V conversion in progress. But needs examined regarding VR and gen. etc. The direct voltage to coil will yield something of interest. At least it will bypass all the ClapTrap,.or is it TrapCrap.........?

IT RUNS!!

I ran a wire straight from the battery to the coil and that did it. I tested spark by hand by touching ground and it had a strong 1/2" spark so I spayed some carb cleaner in and it fired right up! Now I can go through the fuel system and get it running. Thanks for all your help guys.

Don't run it with gas from the tank until the tank and all else it cleaned. I mean cleaned. Then protect the pump and carb with filters.

Good job Coupe'de e9.

I don't know if you want to run on carb cleaner. Regular gas is favored by most people.

I recommend a complete restart/dry start procedure for this trucks motor.

It makes no difference to your problem, is it a 228 or ?

Ed

Flux capacitor. Reference to Back to the Future movie. The ballast resistor block on my firewall reminds me of the Flux Capacitor.

Yes that flux capacitor that I linked-to, above, does state:

Flux Capacitor requires the stainless steel body of the 81-83 DeLorean DMC-12, V6 2.9L , to properly function.

My mind sometimes works in strange ways.

Based on what I have seen in the other replies was a ballast resistor "not" part of the original setup when my 54 235 came off the production line. I am upgraded to 12v. Would it possibly have been added when the previous owner upgraded to 12v? Is there a valid reason to add a resistor when upgrading. The previous owner did a lot of questionable work including the 12 v upgrade. I had to fix a lot of what he did.