Voltage to coil drops to zero when cranking

E-Type
1

Voltage to coil drops to zero when cranking and car won’t start. New generic Ignition switch, coil. All fuses are OK. Car has Series 2 wiring system, neg. grnd. w/ Petronics coil, GM HEI module. Car ran four days ago before loosening distributor to set timing.

Joe

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First thing I would check is battery condition.

You can also measure the voltage drop at the starter though I expect it is similar. Do confirm that the big cable on the starter is reasonably clean and tight - might also see if it gets hot during cranking.

When you say “New Ignition switch, coil” do you mean ‘newish’ or that you just replaced them?

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Battery is great, new connections, connected to float charger, ignition switch replaced this morning. 12 volts to + on coil with switch in on position. Voltage drops to zero when start position is energized. Starter cranks with vigor.

Joe

4

Joe,

Is yours by chance a 1970 or later Series 2? If so, these were fitted with a ballast resistor that was switched into the circuit when the engine was not being cranked. When the starter is engaged, the power to the coil takes a different route, bypassing the ballast resistor. Based on the “binary” behaviour if your problem, I’d strongly suspect that the bypass route is disconnected somewhere. I don’t have the circuit to hand, but it seems likely to me…

Afterthought: bingo. I think the power for the bypass circuit comes from a connection on the ignition switch (that you just replaced…)

-David

3 Likes
5

Joe, If it’s a 1970 or later ballasted ignition circuit, I seem to recall the power to the ballast bypass circuit coming from the starter relay, not the ignition switch. Look at what’s wired to terminal C1 on the starting relay and see if it traces back to the + of the coil.

However, if it’s the earlier non-ballasted S2 ignition, power comes through the Tach on a white wire and should connect to the plus of the coil with the red wire of the pertronix. The black wire of the pertronix connects to the coil neg. I’m going from memory on the pertronix hookup since I don’t have my wring mods in front of me.

You did say it ran until you turned the distributor so check to see if you disturbed the pertronix wiring in the process.
Good luck!
Anthony

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Here’s a recap: Car started and ran well on Friday afternoon with new Petronix Flamthrower II coil and relatively old but reliable Lucas HDI ignition module - no condenser or ballast resister in the circuit. Shut it off, loosened the distributor clamp to check the timing and it hasn’t fired since. Thought it might be the ignition switch so replaced the Lucas switch with a generic four-terminal from NAPA. Tried to start and 12+v on coil drops to 0 when starter is engaged - no spark from HV lead from coil. Jumpered 12v directly from battery + to coil +. Voltage drops to 10v when starter is engaged - still no spark from coil - checked coil lead w/ timing light and no indication of power in lead. Tried all of the above with old Lucas coil - same results. No way to check condition of Lucas HDI unit. Battery is fully charged. Completely mystified. Could new Petronix coil have burned out the Lucas HDI unit? Help!!

Joe

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I believe that is normal.

Other than saying that, you lost me at Pertronix. Once there is failure to proceed with one of those units in place I am unsure what to check short of putting the points back in.

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Hold on everyone…you replaced the coil.
Did you MAYBE put in a coil with a built in ballast?
If so…bingo, you collapsing your own current.
The napa switch is a BIG IMPROVEMENT.
But we are missing something.
Petronix but GM module?
That’s only on a series 3 xj6…UNLESS YOU BOUGHT MY OLD CAR?
GTJOEY13114

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Joe go real slow…read my above first…
1 . do you have a stock distributor with patronix under the bonnet
2. If not what system , post it complete.
3.If you loosened the hold down are you sure when you cranked it that the DISTRIBYTOR DIDNT RISE AND ISNT IN THE SLOT TO ENGAGE?
I think this will help ALOT.
GTJOEY1314

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Joe,

I think it may be time to take a step back and regroup on this issue. There seems more than enough confusion to go around. Firstly, it seems that you don’t have a stock ignition system, so any assumptions about how it is wired (including my own earlier) are probably worthless. You mention the car has a “Series 2 wiring system” but which one? The wiring of the ignition system changed between 1969 and 1970 versions of the Series 2. Some people seem to be talking about a Pertronix ignitor module, but as I understand it the only Pertronix item you have is a Flamethrower II coil - as I understand it, pretty much the same as any other coil. Then there’s the GM HEI module that was mentioned in your original post, that changed to a Lucas HDI module later. I know nothing about either, but maybe someone here does - presumably similar in function at least, to the commonly used Pertronix Igniter module? As your system is clearly not stock, I think we need more information about exactly what components you have, and how they are wired. Otherwise, I fear we are all going to be taking stabs in the dark, and it’s only a matter of time before someone suggests you check your muffler bearings…

-David

1 Like
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Joe I think I agree with David. I have the Pertronix in my E and in two of my '70’s Chevys. I stayed with the stock coil though. None of them have ever given me any trouble but I keep the original points breaker plates in each car so that if the Pertronix does act up I can probably get home. I have only done mods that I can pretty easily take off and go back to original if problems came up. Even though I am an old school guy I hope I never have to play with points again but think I would put them back in if I got into a situation that sounds similar to what you are trying to troubleshoot. My 2 cents if possible for your car.

David
68 E-type FHC

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In case that turns out to be the problem…

:wink:

http://kalecoauto.com/index.php?main_page=product_info&products_id=48

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I had the same thing happen when I replaced the ignition switch. I had to move one of the wires around on the back of the new switch (from Terry’s) to get power back to the coil when turning the starter.

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David,

Thank you for your patient analysis of the confusion I have.caused in my hectic messaging . Here is the condition of my car. It is a 1963 Series 1 FHC with a 1969 Series 2 4.2l engine, trans, and wiring harness transplanted into it, a single-wire Lucas alternator with internal voltage regulator, Series 2 Lucas coil and a Lucas AB-14 HDI ignition module. This system has been running reliably for a number of years. I recently discovered the throttle bushing diaphragms had failed and replaced them. Concurrently, I replaced the spark wiring harness with 8.5 mm wires and replaced the Lucas coil with a Pertronics Flamethrower II coil. Started the car Friday afternoon and it ran well. .Decided to check the timing, shut the engine off, loosened the distributor clamp tried to start the car and no spark. Much fiddling with wiring to confirm that the coil and module were getting power - direct jumper from battery to + terminal on coil,with no luck. Symptom: + coil terminal voltage is 12+ volts when ignition is switched on, voltage drops to zero when starter circuit is energized and engine fires once when starter is disengaged. Question: Could I have fried the AB-14 when trying to start the car with the distributor clamp loose and therefore no ground through the distributor.?

Confusing. Thanks for your patience.

Joe

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Joe,
Apologize, haven’t been following this thread but your symptom is that of a miswired ballast circuit, ask me how I know. Look at a later S2 wiring diagram. The ignition switch sends voltage to the coil via different circuits depending on whether its in the run or start position. You’re not getting voltage in the start position. As long as the coil is designed to operate without a ballast you can simply connect the wire that was intended to go to the ballast resistor to the coil. Alternatively you can probably just jump the start and run pins on the switch together so that 12v is there in either position.
pauls

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Joe,

Thanks for clearing the decks, so to speak… I still have a few questions that I hope will get us there:

  1. You talk about having used a “Series 2 Lucas coil”. Unfortunately, that is not precise enough. Early Series 2 cars used a Lucas coil with 3.0 ohm primary resistance. Later Series 2 cars (1970 year model and later) used a different coil with 1.5 ohm primary resistance, as they added a ballast resistor to the circuit which was bypassed when the engine was cranking. Which Lucas coil did you have? (measure the primary resistance)
  2. You talk about adding a Pertronix Flamethrower II coil. Same question. I don’t know much about these coils, but a google search shows there are many variants. The 45001 has a primary resistance of 0.6 ohms, and the 40011 has a primary resistance of 1.5 ohms. There is also a 3.0 ohm version, and a 0.3 ohm version. I think the “II” after “Flamethrower” is supposed to indicate the 0.6 ohm version, but at least one seller is using that terminology for the 1.5 ohm version too, so it might be worthwhile measuring your new coil.
    As I eluded to in my earlier post, and Paul just mentioned too, your symptoms of 0 volts on the coil “+” when cranking and then the engine fires when you cease cranking sounds exactly what happens with a faulty “bypassed ballast resistor” setup as used on the later Series 2s. I had the same thought as you about damaging the ignition module when you loosened the distributor and potentially lost the ground path. My other thought now is that you may have replaced a Lucas coil with 1.5 ohm or 3.0 ohm primary with one with a 0.6 ohm primary. However, if that had the potential to damage something, you’d think that the engine wouldn’t have run OK before you decided to check the timing. I’m sorry that I’m not familiar with the Lucas AB-14 HDI ignition module, or it’s purpose, or where it fits in your circuit. Hopefully someone else is, as without this knowledge, I don’t think I will be able to assist much.

-David

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Joe, it fires once? Please explain/describe this to us in more detail.
Anthony

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Again, these are exactly the same symptoms that I had. NO power to the coil while cranking and the engine would fire after I released the starter. I suggest you go back and find out which wire is messed up behind the new ignition switch.

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Joe,
A miswired ballast circuit will fire once (or sometimes start) as the engine is still spinning from the starter motor when the ignition switch is returned to the run position and the missing coil voltage is returns. My '70 always started (lucky) when I went from start to run position but never fire during cranking. It was a puzzle that caused other issues when the incorrect coil is used as well. The ballast system is simple but won’t work unless, the coil and ballast are designed to work with each other and wired correctly.
pauls

1 Like
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Gentlemen, thanks for all of your replies. First, no ballast on the ignition; it has a Lucas AB14 electronic ignition module which replaces to conventional points in the distributor. The Pertronix coil is a 0.6 ohm coil. My description of the “start” on disengaging the start circuit on the ignition switch is just a “burp” caused by, I think, the instantaneous return of voltage to the circuit. I believe the suggestion that I have the ignition switch mis-wired might be correct. I’ll go fiddle with the wiring to see if I can get the coil voltage to remain 12+ volts when the starter circuit is energized. This may soon set a record for thread length on J-L. Thanks for your determination.
Joe