There's a lot of info from the CJ-3B Bulletin Board on this page: a description of the ignition system, some troubleshooting examples, several approaches to testing the circuitry, and a final reminder to check the most unlikely problem area -- the ignition switch.
Perreault was wondering about the coil: "The coil on my 3A, with a 2A engine, has got 2 little nuts with a + and - sign, and a wire that goes to the distributor Auto-Lite IAD 4008 From my description one could determine that I am not a mechanic -- Ha Ha. Coil looks very old. With the exception of Made in Canada stamp on top of it there is no tag, serial number etc. Considering who I bought theJeep from I would not be surprised if it come from an old tractor. I checked on the internet and my service manual and could not find a method to determine if it is performing OK. Do you know of one? How much voltage should an OK 6-volt coil generate?"
Oldtime: "Many people have been asking about Jeep wiring here on the B.B. Here is a description of the very basic circuitry needed to run (not start) an engine. So use a hand crank if need be. No special tools are needed for these tests. Engine ignition tuneup should be covered separately. That would entail detailed specifications and inspection of all individual primary and secondary ignition components.
"The engine ignition circuitry is composed of two parts. The primary and the secondary circuits. What do we mean by this? The primary circuit is the current flowing from battery positive (+) back to battery negative (-) through the closed breaker contact points (black in the diagram.) The secondary circuit is through the spark plug gaps when the breaker contacts open (red in the diagram.) The engine ignition circuitry is a continuous vacillating impulse of interrupted current flow as the mechanical breaker opens and closes.
"There are two variations of the complete ignition circuit used for the CJ-3B. This depends on whether the Jeep has the old-style instrumentation and its associated floor starter, or the new-style cluster gauge and its associated key start switch. For simplicity of explanation and testing we will bypass the starter, gauges and switches. We will 'hotwire' the engine ignition. The 'hotwire bypass' is very desirable for testing only of the basic engine ignition circuit.
"This wire runs straight from the battery positive + post to the coil + terminal. That's it. That's the basic key! This primary ignition current then continues on through the internal primary coil winding and exits the coil at the negative - terminal. Now the circuit goes from this - terminal into the distributor. Here the wire terminates into the condensor and also the insulated mechanical circuit breaker arm inside the cap. When the breaker points are closed the current flows onward into the distributor body and engine casting. Then onward through the engine ground stap to the frame. Lastly from the frame ground strap to the negative - battery post. That's the complete hotwired primary circuit.
Note: see also Jyotin's "3BCJ" Hot Wire Box.
"The secondary circuit kicks in as the primary is left open by the mechanical breaker arm. Again the current flows from the battery positive + to the coil + terminal. The open breaker allows the condensor to reverse current flow back into the primary coil winding. Current then travels through the secondary winding which begins at the + coil terminal and exits the coil high tension tower. Here the high voltage, high tension current travels along the coil cable into the distributor cap tower. The rotor sends this current onward to the indexed spark plug cable, either # 1 3 4 or 2. Next the current runs down that plug cable where it jumps the plug gap and on into the engine casting. It is important to note here that only clean spark plug threads allow uninterupted current flow into the engine casting. Next current travels through the engine ground strap, and onward through the frame ending back at the battery negative - .
Jyotin interjected: "I'd like to offer a dissenting opinion on your notes on the secondary circuit operation. The condenser does not have anything to do with creating the voltage in the secondary. In fact, one could remove the condenser altogether and the Jeep would still run (for a while), perhaps 50-100 miles or so until the points were so burnt and pitted that they no longer would make effective contact. The condenser filters out (shorts out) the arc in the primary circuit caused by the opening or closing of the points and shunts the arc that would otherwise be across the points to ground to keep them from burning and pitting. It is the collapsing of the primary field when the points open that generates a voltage in the secondary. That is what is passed to the spark plug. The primary coil will generate a voltage in the secondary when there is a change in the current going through it. Both opening and closing the points creates a change in the current through the primary, and thus a spike in the secondary happens at points open and points closed. The condenser shunts the spike around the point in both cases."
Oldtime: "Jyotin, thank you so much for your dissention. I am not the final authority on anything. I can learn from you and perhaps you can learn from me. Your explanation of the condensor's function is excellent although I believe slightly incomplete. You have described the main function of the condensor. Here is what I believe to be correct beyond your explanation: The collapsing of the primary field is initiated by the opening of the primary breaker then accentuated by a reverse surge from the condensor. The condensor in this instance can discharge more quickly by reverse flow than through the dielectric grounding process. I believe the condensor provides for greater voltage increase due to quickened magnetic depolarization.
"I did not state that the condensor created voltage in the secondary. I stated: 'The open breaker allows the condensor to reverse current flow back into the primary coil winding.' According to Willys-Overland: 'The condensor prolongs the life of the distributor points by preventing arcing at the contacts. It also provides a hotter spark by creating a reverse surge of current which rapidly breaks down the magnetic field of the coil by demagnatizing the core. Should the condensor be leaky a weak spark will result.'
"Furthermore all voltage is generated by the battery source. Not by the mechanical act of the breaker nor the collapse of the primary circuit. The secondary circuit is available merely because the primary is not. The secondary coil windings increase battery voltage while decreasing amperage. This exceptionally high voltage allows the current to travel the open gaps. The ultra high voltage does not travel via the circuit breaker so the gaps jumped are the rotor to cap and spark plugs. Beyond this you are correct. The condensor protects the points from the lower voltage arc of the primary current. Now we have gone far beyond basic circuitry."
"First remove the distributor cap clamps. Now turn the engine crankshaft to close the breaker points. Remove the high tension cable from the center of the distributor cap. Now fashion and install a "hotwire" from the battery positive + post to the coil + terminal. A small spark should be detected as the wire is attached because you have just closed the primary ignition circuit. To make a basic coil test, hold the end of the coil cable about 3/8" away from an engine surface (ground). Open the contact breaker with a stick. A strong spark should jump the gap between the coil cable terminal end and the engine ground as the breaker is opened. A good spark will jump up to 1/2" gap.
"If by chance you don't have + and - terminals indicated on your coil, then hook up either terminal in series. The coil should function even when reversed although not correctly. So now we will check the direction of current flow, or polartity. Pull the high tension cable from the distributor cap. Now slide the cable boot back up out of the way. Tape a regular sharpened pencil onto and up even with the cable terminal end. Hold this arrangement up near the engine ground so that the pencil is half way between the cable terminal end and the engine ground. Open the breaker points. A spark should jump this 3/8" gap. If the spark usually jumps from the pencil lead to the ground your coil polarity is correct. If the spark seems to jump all the way from terminal to ground bypassing the pencil reverse your coil wires and retest."
Drac stepped in to try and actually answer Perreault's original question: "As I recall, the voltage produced by the coil should be in the vicinity of 18 to 20,000 volts, producing about 2 to 3 amps. This is why the old point-type ignition started a flooded engine easier than todays electronic ignition. It produced a much hotter spark. The amperage produced by electronic systems (at least GM's) is only about .5 amps although the voltage is high, approx. 45,000 volts. This is one reason why a tune-up isn't required at the old 12,000 mile intervals anymore. The reduced amperage from the electronic ignition doesn't burn out the plugs nearly as fast as point-type ignition."
Billy added, "If you need a new coil just find one that's for 12 volts that requires an external ballast resistor, they're the same."
Oldtime: "Yes, Billy is correct in that a 6-volt coil is basically the same as a 12-volt external ballast coil. However exact primary and secondary circuit resistance can and does vary from one coil to the next. That's why we have part numbers. This can and does effect condensor capacitance for the primary. This can and does effect spark plug heat for the secondary. Hotter coil, hotter plugs? Condensor values will be effected! This is really going into the topic of ignition component relationships which is detailed tune-up information. Perreault, check the coil amperage and voltage from + to - . Engine off: 5 @ 6.3V. Engine at 600 rpm idle: 2.5 amperes. Poor Perreault probably wishes he never heard of The CJ3B Page by now. Hope somebody has answered your concern, Perreault. "
Ron posted this: "Pulled #1 plug to check for fire and got a strong initial spark followed by weaker sparks. Set everything back to TDC again and tried the static time method with #1 spark plug. Again a strong initial spark followed by no spark at all. ARGGGH again. Out of frustration I moved the dist. to it's max. travel back and forth rapidly and noticed a weak spark. When moved slowly I get no spark. What's going on?The condensor is new and is good. What do I need to check now and how?"
Eric Lawson asked, "I'm going to assume you have the ice pick style of test light. If not, just substitute the free wire (the one that isn't hooked to ground) for the probe and you'll be fine.
"Test 1: Hook the wire end of the test light to the negative terminal of the battery and then touch the probe (ice pick end) to the positive terminal of the battery. This will tell you the light is working and give you an idea of how bright the light gets when supplied with 12 volts. If the wire is long enough to allow it to remain on the battery negative terminal, while making the other tests, leave it there. If not, move it to something that is connected to the engine block, such as the studs that hold the ignition coil clamp onto the engine. Make sure this is a good and clean connection.
"Test 2: With the wire hooked somewhere on the block or to the negative terminal of the battery (the wire is hooked to ground), touch the probe of the test light to the igntion coil terminal that has the wire that goes to the ignition switch. The light should light up when the ignition switch is 'on' and be dark when the ignition switch is 'off'. When the light is lit, since you have a coil with an internal resistor, it should be as bright as it was when hooked to the battery. If the light is much dimmer than expected, goes on and off or doesn't come on at all when the igition is on, then you've got a problem with the ignition switch or the wiring between the ignition switch and the coil. Do cehck to make sure the ground connection on your test light is good and try a different connection point for the test light ground lead.
"You might also have special resistance wire between the ignition switch and the coil (see below for more info). It is possible that the problem is before the ignition switch, but since the gas gauge is wired to the same place on the ignition switch that the coil is connected, a bad ignition switch or bad wiring before the igntition switch would likely also cause problems with the gas gauge reading.
"Test 3: "For the next test, you'll need to pop off the distributor cap. I would also pull the plug wire off of the center tower of the distributer cap and move it so it's metal piece is almost (1/16-inch or closer) touching some metal on the engine block. Leave the other end of the spark plug wire connected to the high voltage tower on the coil. The voltage on the high voltage side of the coil rises to meet the challenge of arcing across something. Sometimes, if the gap is large, the coil can be hurt. Move the engine around so the distributor points are closed (touching one another). Turn the ignition switch on and touch the probe to the coil terminal that has the small wire that goes to the distributer points. The light should be off. Use a small chunk of wood or hard plastic rod to push open the distributor points. You can also rotate the distributer so the points open. The light should light up when the points open. Depending on the test light, it will light up anywhere from the same as it was across the battery to a little bit dimmer. That isn't very specific -- here is where a voltmeter would 'shine.'
"If the light is very dim, but doesn't go completely out, when the points are closed, you probably have bad points. If the light never lights up, disconnect the small wire going to the distributor, leave the ignition switch on, and touch the probe back to the same point you just used (the terminal on the coil that had the small wire going to the distributor.) If the light stays off, the coil is bad. If it lights up, reconnect to the coil the small wire that you just disconnected, and disconnect the condensor.
"Push the points open and again touch the probe to the same terminal on the coil. If the light lights up, the condensor is bad. If the light still doesn't light, you'll have to inspect the small wire's insulation as it enters the inside of the disbributor body and also the points themselves to figure out the problem. Either the insulation is bad where the wire enters the distributor body, or something is wrong with the points. Since you have a weak spark and you've tried a new coil, perhaps you have special resistance wire between the ignition coil and the ignition switch. You can connect a wire from the battery to the small terminal on the coil that has the wire that goes to the ignition switch and then check the strength of the spark. If the spark improves, this is more evidence that the wire to the igntion switch is bad or that the wire is that special resistance wire. Note that the resistance wire is the small wire that goes between the ignition coil and the ignition switch. The resistance spark plug wire is something else entirely. Sometimes the low voltage resistance wire was used in place of a ballast resistor. If none of this seems conclusive, then it's time to look at the high voltage side of the ignition system. The voltage in this part of the system goes very high -- enough to jump a gap and make an arc, but no higher. If there is a sneak path to ground, then the voltage will be bled off before it can get high enough to make a good strong spark. Have you moved the spark plug wires around to put some distance between a piece of metal and a possible bad spot in the plug wire insulation? Have you tried a new distributor cap or rotor?"
Oldtime agreed: "Absolutely top notch advice. I will add that if you have a high voltage (secondary circuit) bleed or short, this can often be readily detected in dark conditions. Example a bad distributor cap with hairline cracks will 'lite up' at night."
Ron: "Tested everything today with normal readings with meter. Grounded the coil wire 1/4 to 1/8-inch from block to check coil spark and had a blue spark at the points but an orange spark from the coil to dist. wire. I disconnected the coil positive wire and used a jumper wire straight from the battery with the same effect; no blue spark from coil wire. I got the same battery voltage readings from the coil positive side, coil neg. side, and dist. from coil post with the points open. As far as I can tell the the points aren't grounded out and the dist. body to ground check passed OK."
Eric Lawson: "If you are getting a 1/4-inch long spark, I don't think the color of the spark is important. How noticeable is the spark across the points? It shouldn't be too big. On my Jeep, the spark across the points is only seen in the dark."
Ron: "Good news, bad news. I double checked point gap before firing the engine up. Before I went through this tear down and re-do I had the dwell set at 42 degrees as the service specs said. However, this moved the point gap from 0.020 to roughly half that. I've read that if the gap is set correct (from high point of cam lobe) then the dwell should be right also. Anyhow, she fired right up with the correct point gap. I adjusted the timing with a light and let her run a while noticing no popping from the exhaust pipe as before. I checked the dwell reading while running and it read 40 degrees. Will this 2 degrees make a difference, or just stick with the point gap and leave it alone? Bad news is the oil pump gasket needs to be replaced from moving the pump so much. No big deal, just gonna be messy. I know ya'll are tired of hearing 'bout this but I sincerly appreciate all of your help!"
Oldtime: "We never tire of hearing about Jeep concerns. We are The CJ3B Page. I believe the spark color is attributed to such things as the type of conductor material (metal) and the presence of other substances such as carbon. Now onto dwell (also correctly referred to as cam angle) and the point gap. As you know the point breaker gap affects dwell and vice versa. A narrow breaker gap causes the Jeep to run poorly at idle speed and increases breaker point arcing. Opening the breaker gap wider fixes that condition but causes the dwell time (duration time between breaker closed to to breaker open) to shorten. A shortened dwell time will cause the Jeep to run poorly at higher RPM's. So this is a give and take scenario. A multitude of small factors affect the precision of ignition timing. Example: Flat-bladed feeler gauges will give you an oversized point gap, therefore wire feeler gauges will be more precise. Better yet have the breaker gap set with a dial indicator. Better still have the distributor adjusted upon a distributor adjusting machine. Perhaps someday given some real time we can de-mystify and bring real understanding to the simplicity of Autolite ignition. In the meantime spark another conversation so that we don't dwell on the Autolite ignition topic too long. We're all glad you got it going."
North Carolina Nick stopped by, looking for a way to test his spark plugs. He asked: "I need a cheap, easy way to see if I am getting spark at each plug. Does anyone know of a way?"
Maxx suggested: "Use a timing light. Hook it up to each plug wire one at a time."
Rus Curtis replied: "While the engine is running, I gently pull off the wire from the individual spark plug and note two things. If the spark plug is getting fire, you will hear, and possibly see, the arc as you clear the boot from the top of the plug. If you continue to pull the wire away from the plug to where it's too far to arc and it breaks connection, you should hear a drop in the RPMs or it will idle rougher than before. If the idle doesn't change, chances are the plug is bad. If there's no arc to begin with or if it's erratic, then the problem is with the wire or upstream at the distributor. This can be done with each plug to see if it is getting fire. WARNING: If you are touching the fender or your other hand is on the valve cover or anything else that conducts on the Jeep, you will become part of the circuit and it will wake you up! Chances are you'll drop the wire so that you can shake the smarts off of your hand."
Eddie mentioned: "A spark plug tester works great. It goes in between the plug and the wire. If you are getting spark, it will light up. They are available at most parts stores for 5-10 bucks."
Jyotin had another option: "Remove the number one spark plug. Leave the rest installed. Ensure that the base of the spark plug is grounded well and then crank the engine. If you have any questions about whether or not you have a good ground, you can connect a test wire from the spark plug base to ground on the battery. Watch for a spark across the gap of the plug. It should be a good, healthy spark, not some wimpy, barely visible arc. I would do each spark plug one at a time if you use this method because you are cranking fuel through the engine and it may start on three cylinders. You can see if you are getting any spark at all by cranking the engine until the points are closed. Leave the ignition switch on and then take the distributor end of the coil wire and hold it near a good ground. With a non-conductive tool, a wooden matchstick would work well, open the points. You should get a spark from the coil wire to ground. WARNING: If you have a leaky coil wire and you are holding it, you will get a wake up shock, but it won't hurt any more than if you had a close encounter with an electric fence."
Derek asked for advice regarding his distributor, saying that he thought he had high voltage coming from the coil but not getting to the plugs. And he didn't have a timing light available.
Larry suggested: "If you're sure that 12 volts is going into the distributor from the coil and the coil is good, points are good and set correctly and you're still not getting any fire through the plugs, the condensor is probably bad. Same thing just happened to one of my vintage farm tractors. (Now you know why I think so much of the electronic ignition kits as all these type problems just don't happen.) Also check the rotor and clean it good; same with the cap and make sure it isn't cracked. One of the biggest problems I've run across with folks replacing distributors is that many install it 180 degrees out (really does a number with the timing), and/or the plug wires are crossed or backwards."
Another reader remembered, "On my Jeep I found that the insulation around the post that sticks out of the side of the distributor was bad and allowing the system to ground out there. Fabbed up some new insulation pieces from old inner tube and the Jeep fired right up. It acted kind of like the capacitor was bad."
Don Norris suggested the test procedure outlined in Ric Meagley's article L134 No Spark?.
But Oldtime was up to the challenge of testing without special tools: "For speed in diagnosis I give preference to knowledge, along with the simplest of tools. Simple is good! Although the link Don provided is quite valid; it entails use of test equipment that is not always accessible. I suggest you first try to eliminate all neon lights, testers and other gadgets.
"Let's look into your primary circuitry and make sure it is fully functional. Do this before you progress onto the secondary circuitry. I will try to be as clear as seems practical.
"This concludes a basic quick check of the primary system. If all looks good with the primary circuitry let's proceed on with simple observations of the secondary circuitry.
We have now completed a simple test of both the primary (low voltage) and the secondary (high voltage) engine ignition circuitry. These basic simple tests are particularly appropriate for field service.
Most of us have probably troubleshot a problem, be it with our trusty old Willys or some new gadget, that has just eluded us. We've read and reread the manual, spent nights and weekends covered in grease and even after throwing a week's wages at it, it continues to plague us. At this point, if your problem is with your CJ3B, a smart high hood owner will come looking for some advice on The CJ3B Bulletin Board.
This is just what Ron did. He said: "The engine will not start; I was told when I bought it that it was running. I have been sinking money into it just to get it to start. I put in a new coil, points, condenser, cap, wires, starter bendix, Solex carburetor and plugs. If I pump the accelerator 20 to 25 times it will cough and run for a few seconds. If I choke it and have a heavy hand on the starter it will cough and run for a few seconds. It acted the same with the YF carburetor on it. I checked the carburetor installation several times. I also checked for water in the fuel tank. The plugs are blackened now."
Gale W. Ray replied: "Sounds like a fuel delivery problem to me. Plugged filter, plugged line or bad fuel pump would be the first place I would check. My jeep had a piece of firewood stuck in the line just before the fuel pump. It would run for a short time and then die. Then it would crank up again in a few minutes."
Glenn Smith suggested: "Even though the plugs are new, you might try replacing them again. I've found that it doesn't take much to foul them. Also, you might try marking the distributor position, then loosen it and try moving it while someone else tries starting the Jeep. You say you checked for water, but is the gas fresh? How about the exhaust, not blocked? Perhaps it's a loose wire on the ignition switch? Is the condenser bad; new doesn't always mean good."
Steve proposed a way to find out if this was a fuel problem: "If you can keep it running by carefully and repeatedly spraying a tiny amount of starting fluid down the carburetor as it sputters, then you have a fuel delivery problem. The most common fuel problem in old jeeps is simply crud in the tank and/or lines. Have you used a flashlight to look down into the mouth of the tank to see if you can see any sediment or debris? Try removing the line from the input to the fuel pump and using compressed air to blow the line back into the tank." Ron provided an update: "I replaced the fuel line and filter, blew out the fixed line at tank and replaced the fuel pump; I have the same problem. Installed fuel regulator and checked fuel pressure: 4lbs. I cranked the engine with fuel line in Mason jar with plenty of fuel and no water. Set fuel regulator to 3 lbs; same problem, didn't start, it just coughs and runs for a few seconds. I tried to move the distributor in small increments and got black smoke out the carburetor with light mist of fuel. I pulled the plugs and grounded them to the block this evening and had good spark on all four. I also pulled out the plugs and manually turned the engine to where number 1 piston was at the top, the timing mark lined up and the rotor location was as close as I could tell on the number 1 plug wire. No loose wires, but I have not checked the exhaust yet."
HWooldridge commented: "If the float sticks and the needle is blocked, it will flood and act like this. My jeep was restored last year and ran like new. I drove it regularly and then parked it for four weeks this winter, when it started fouling plugs and refusing to run. I had to pull the carburetor apart and blow out the needle seat to the bowl. I never found the trash but there was something very small in there preventing the needle from seating.
"Another thing to check is whether compression is low and you are oil fouling. Before I rebuilt my engine, I could put a fresh set of plugs in and they would foul in 15 to 20 minutes at idle. If you have a vacuum leak, it could be in the PCV line or around the manifold. If the PCV is sticking, it will not run correctly. Pull it off and clean with brake cleaner, and then reassemble or just plug that line and see if your problem goes away."
Tom Callahan inquired: "By any chance did you do a compression check on the engine? If your Jeep has sat idle for a period of time, I'm wondering if you may have low compression due to a stuck valve. It is fairly easy to pull the valve cover and check the intakes, but the exhaust valve cover may be a bit more challenging. Steve's trick with the starting fluid will rule out an open valve if you can manually get the engine to run."
As with most problems, there comes that time when you know that you're victorious. A turn of the key or a press of the foot starter and your 3B roars to life, purring like the day it rolled off of the assembly line. Ron said: "I tried running with starter fluid, new plugs, checked the exhaust system, blew carburetor cleaner in the carburetor, checked fuel pressure again, capped PCV at manifold, did all I could think of and still nothing.
"I decided to go through the ignition again. I statically set timing and points and then pulled plugs looking for #1 at TDC. I cleaned plugs and re-set gap. Tried starting engine and it would run two to four seconds and then shut down. Set up timing light and asked my wife to start engine. No strobe on timing light. Asked for a restart and got strobe; the engine ran for a few seconds and I then lost strobe. I pulled out my jumper wire and hot wired the ignition. The CJ now ran like a beaver.
"The contacts on the hot side of the ignition switch are vibrating with the engine harmonics and breaking contact at frequent intervals. I found that if I hold the key with a downward torque, the engine would stay on line."
Ron was not the only owner that had this problem. Bob stated: "My key switch went bad last year. It had more to do with the connections of the wires rather than the internals of the switch. I replaced it with a common key switch that also has a starter position for a solenoid; I just don't use that function of it. If you want one without the solenoid part, I would check a place like Tractor Supply or even a motorcycle parts shop."
Ed Wilson agreed: "I had similar running problems last year. I mentioned it to the guy that rebuilt my engine. He said it might be the ignition switch and sure enough, it was."
Thanks to all the contributors, and to Doug Hoffman and Ken Bushdiecker for editing.-- Derek Redmond
Also on The CJ3B Page, see more F-head Ignition Tech Tips and Jyotin's "3BCJ" Hot Wire Box.
Elsewhere on the web, see L134 No Spark?, and more details on this type of ignition system and the man who invented it: Charles Kettering and the Kettering Ignition System.
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