I'm having an issue where the car doesn't want to fire when warm (fresh build/restoration) so I measured the coil and ballast resistor voltage when warm (engine not running). In the run position it was 4.8V/6.0V respectively which seems low. I had just tightened the neg wire on the coil which wasn't as tight as it should be and the car did fire so no idea yet whether this was the issue or not. All the engine bay wiring harnesses and battery are new as well as the Mancini distributor, orange box and resistor. Any thoughts on those voltages?
What should coil and ballast resistor voltage be?
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MOPAROFFICIAL
If it has tits, it's a liabilititty.
Whats the voltage read going to the ballast? Should be 12+
11.7 V and the battery is 12.7 V
Dartswinger70
Well-Known Member
I think its 12 volts in to the ballast resistor and then out is 9 at the coil I know the ballast drops it a bit maybe by 3 volts etc. I may be thinking of points also they can burn up if key left on etc. OP check fuel etc if engine is warm some of this modern gas boils off when sitting etc. Fix for me was a phenolic gasket at my carb.
MOPAROFFICIAL
If it has tits, it's a liabilititty.
Like he said, 9 or so volts out of the ballast to the coil is norm, should be no drop to the ballast though
Its getting fuel. The ballast resistor drops it from 11.7V to 6V. Its the one Mancini provides.
MOPAROFFICIAL
If it has tits, it's a liabilititty.
Maybe it's on its way out ...
It doesn't have 2 hours on it. You think it would work or not. I checked the resistance at 1.4-1.5 ohm. I have a spare 4 post ballast. I'm also going to check the coil voltage in the start position next time I get a no start condition.
MOPAROFFICIAL
If it has tits, it's a liabilititty.
Then a wire has resistance/is getting really hot. Power from the key/ign switch?
Test them all next go around.
I was originally thinking the no start condition might be an ignition switch issue. I'll have to do some more testing and check voltages with the engine running.
That voltage will VARY according to supply voltage, the ballast, the coil, and the temperature.
When you twist the key to "start" the entire "ignition run" (IGN1 terminal at the switch) GOES DEAD. The starting voltage comes from the ignition switch from the IGN2 contact, which is seperate from but works like the "start" contact. IE IGN2 is live only when cranking. THAT wire, normally brown, goest to the coil + sided of the ballast, and is supposed to supply battery voltage direct to the coil when cranking.
I've written hundreds of posts on these issues. VOLTAGE DROP in the various bulkhead connector terminals, specifically the big black and big red ammeter wire terminals, the terminals at the ammeter and the ammeter itself, the connector for the ignition switch and drop within the switch contacts, and drop through the bulkhead connector terminals for the IGN1 and IGN2 circuit.
"For now" your "run" coil voltage is fine
Put your meter on coil + to ground, Crank the engine USING THE KEY and read the meter while cranking. You "should" have same as cranking battery voltage, and should have a minimum of 10.5V
Now, the ECU still has to get power when cranking. HOW does that work? When cranking, and IGN2 is activated and powering the coil direct, IGN1 is disabled, so the ECU would not get power. BUT POWER ACTUALLY backfeeds through the ballast and to the ECU, so the ECU fires the car on REDUCED voltage.
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11.7 volts is about right. The gauges etc will be drawing current & you will also be getting voltage drop through the wiring harness as it is supplying the coil.
Voltage drop across the bal res seems high though. If it was my car, I would p**s off the bal res system & run a 4 pin HEI module & e core coil. No bal res & you can 0.060" plug gaps because the system is more powerful.
Voltage drop across the bal res seems high though. If it was my car, I would p**s off the bal res system & run a 4 pin HEI module & e core coil. No bal res & you can 0.060" plug gaps because the system is more powerful.
Dartswinger70
Well-Known Member
the balast resistor is desgined to drop the voltage to the coil I believe Id say to 9 volts or something like that.
Temperature related failures are common to any ignition module. Some come back when cool several times before failing completely
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I took it for another test drive (fresh restoration) and came home to found a bunch of coolant sprayed around the engine bay. It looks like the upper rad hose clamp was loose...easy fix. It wouldn't start when hot again and I tested voltage at the ballast when cranking.....10.5 volts. I jumpered the starter module to ground (already has one ground as the clutch switch is not connected) and that wasn't it. I'm thinking its not an electrical issue. I then got in the car again and tried to start it holding the throttle pedal to the floor and it started. 
Thats counter intuitive to me but I'm not going to argue with it.
Thats counter intuitive to me but I'm not going to argue with it.
That reads like perculating fluid. Fuel and spark. If it ain't one it the other.
You can easily check for spark. Please re-read my description. IT IS IMPORTANT to understand how that circuit operates, and one HUGE caveat is to understand the difference in the circuit between cranking the engine by jumpering the start relay, and instead using the key as normal
When jumpering the relay, the start/ bypass circuit is not engaged, and so this greatly changes things electrically. So when testing for spark while starting...........
When jumpering the relay, you have much less power to the coil, as the power is still going to the coil through the ballast, but the battery, now cranking the engine, is down to say, 10.5--11V. This does not seem like much, but 10.5 is comparable to 120V AC. Would you expect "stuff" in your house to operate correctly if all the house outlets were down to 105V instead of 115-120? THAT IS APPROX a 20% change!!! That's like having $120 in your pocket and tossing 20 out the car window!!!
Get a spark gap or "rig" a spark plug by greatly opening up the gap, or cut the ground electrode off. DO NOT use a radio suppressor coil wire for testing. You cna even use low voltage wire if you "hang" it in air so it doesn't arc against ground. "Rig" the spark tester so you can see it through the hood gap, or round up your girlfriend. When cranking, and using a metallic core coil wire, you should get nice hot snappy blue spark at least 3/8 and typically 1/2" long. These should be "in rhythm" and not jerky and intermittent.
Once you have convinced yourself that the spark is dependable, concentrate on carb boiling/ vapor lock. "Modern" oxygenated and or alcohol containing gas boils off much worse than "old school" gas.
Might also pay to inspect the distributor for shaft wear, stuck advance mechanism and other problems. You might still get spark, "sometimes" but rust, debri, damage, wear, could cause intermittent operation.
When jumpering the relay, the start/ bypass circuit is not engaged, and so this greatly changes things electrically. So when testing for spark while starting...........
When jumpering the relay, you have much less power to the coil, as the power is still going to the coil through the ballast, but the battery, now cranking the engine, is down to say, 10.5--11V. This does not seem like much, but 10.5 is comparable to 120V AC. Would you expect "stuff" in your house to operate correctly if all the house outlets were down to 105V instead of 115-120? THAT IS APPROX a 20% change!!! That's like having $120 in your pocket and tossing 20 out the car window!!!
Get a spark gap or "rig" a spark plug by greatly opening up the gap, or cut the ground electrode off. DO NOT use a radio suppressor coil wire for testing. You cna even use low voltage wire if you "hang" it in air so it doesn't arc against ground. "Rig" the spark tester so you can see it through the hood gap, or round up your girlfriend. When cranking, and using a metallic core coil wire, you should get nice hot snappy blue spark at least 3/8 and typically 1/2" long. These should be "in rhythm" and not jerky and intermittent.
Once you have convinced yourself that the spark is dependable, concentrate on carb boiling/ vapor lock. "Modern" oxygenated and or alcohol containing gas boils off much worse than "old school" gas.
Might also pay to inspect the distributor for shaft wear, stuck advance mechanism and other problems. You might still get spark, "sometimes" but rust, debri, damage, wear, could cause intermittent operation.
As per my post I was jumpering the ground terminal on the relay to ground for the clutch safety switch not jumpering the start circuit. The distributor is new.
I'm still dealing with this issue although I haven't been driving he car the last few weeks. I put in another known good coil. It wouldn't start (at least easily) when hot again. I checked the voltage across the coil and it was 5V/8V RUN/START. I should have tried applying 12V directly to the coil to see if it resolved the problem. Here are some more numbers from my testing. All engine bay wiring, distributor, ECU and ballast are new. I'm not sure what to check next.
12V to ballast - key in RUN - not running
6V out of ballast - key in RUN - not running (coil draws current to cause a voltage drop?)
10.5V to ballast cranking (is that an acceptable voltage drop? Does it point to firewall or steering column connector or column switch issues?)
5-6V across the coil in RUN - low
8-9V across the coil in START - low. If there is 10.5V to the ballast cranking why only 8-9V across the coil?
The battery is well over 12 volts with no charging and higher when running.
If you have 12 volts at battery you want close to that everywhere it should be, i.e. both sides of amp gsuge, ignition switch, headlight switch, lighter well, etc.. Where your voltage drop is? Good hunting
I'm not great at electrical but I'm scouring the electrical diagrams as we speak. I will check the resistance across the starter switch harness terminals...red to brown in start position first (?)
Do not try to troubleshoot voltage drop problems with resistance tests, generally speaking. You are FAR better off getting the circuit "normal" and testing it for voltage drop under LOAD. This means, EG, if you have a slow starter, you are measuring voltage across the length of the main battery cables, and from the starter to ground, etc, etc, while the starter is cranking
Likewise, other circuits should be measured while operating. Mose voltage drop problems are ANY "connection" or switch contact. So "let's say" ignition switch the red battery supply, the crimp between the wire and the terminal at the switch, the connection between the wire terminal AND the switch, the switch internal contacts, and the same terminal and terminal to wire potential problem at the other side of the contact, just as example.
Take a wiring diagram and draw the part out that matters. EG the path from the battery, fuse link, through the bulkhead, through the ammeter, tap off the welded splice, feed to the ign switch, out of the switch on the ign 'run' line, through the bulkhead, and all the connections that branch off that, electric choke, alternator field, VR IGN terminal, feed to the ignition system, smog doo dads on some models, etc etc etc. And start taking measurements and writing them so you can see what is happening.
Such things as heavier duty signal lamps and trailer pulling is not only subject to drop due to what has been mentioned, but by the WIRING ITSELF, because headlights, tail/ signal wiring is known to be marginally small. Just an example.
Likewise, other circuits should be measured while operating. Mose voltage drop problems are ANY "connection" or switch contact. So "let's say" ignition switch the red battery supply, the crimp between the wire and the terminal at the switch, the connection between the wire terminal AND the switch, the switch internal contacts, and the same terminal and terminal to wire potential problem at the other side of the contact, just as example.
Take a wiring diagram and draw the part out that matters. EG the path from the battery, fuse link, through the bulkhead, through the ammeter, tap off the welded splice, feed to the ign switch, out of the switch on the ign 'run' line, through the bulkhead, and all the connections that branch off that, electric choke, alternator field, VR IGN terminal, feed to the ignition system, smog doo dads on some models, etc etc etc. And start taking measurements and writing them so you can see what is happening.
Such things as heavier duty signal lamps and trailer pulling is not only subject to drop due to what has been mentioned, but by the WIRING ITSELF, because headlights, tail/ signal wiring is known to be marginally small. Just an example.
[1] The measured voltages look ok.
[2] Try another coil & module.
[3] Still not starting when hot?
[4] Get a helper. Connect DVM to coil + terminal. Check for voltage while cranking. All good?
[5] Might be fuel related, flooding.
[2] Try another coil & module.
[3] Still not starting when hot?
[4] Get a helper. Connect DVM to coil + terminal. Check for voltage while cranking. All good?
[5] Might be fuel related, flooding.
I did some voltage testing at the column switch harness connector. I was getting 9.7V to the brown wire when cranking. I then tested the red power wire going into the connector and only get 9.9V cranking. Battery is over 12.5V. The engine harness is new. Perhaps I need to pull the bulkhead connector and see what is going on with the power connector wire (terminal J according to the diagram). I'll test power into the bulkhead at the blue wire first to make sure there is no issue on the engine side.
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