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EFV-8 Club Forum / General Ford Discussion / '41 V8 - Coil Circuit / Resistor Replacement

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Discussion Topic: '41 V8 - Coil Circuit / Resistor Replacement

plenker

07-14-2014 @ 1:32 PM

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My SD Convert has been having starting issues - particularly on re-start when at normal operating temp after brief shutdown. Changed coil / resistor / checked voltage thru ignition switch to coil found new replacement resistor was not providing proper voltage. The resistor I replaced was also a new replacement so now, I have a lack of confidence in vendors supplying new resistors with proper ohm rating. Can anyone tell me what that ohm rating should be? I experimented with a different resistor (from a Dodge but a different application) that at least seems to provide proper voltage to coil and car seems to be starting properly. What I'd like to hear from someone are the exact specs on the proper Ford resistor - plus perhaps a vendor that can provide such a resistor. In addition, with this Dodge resistor although it seems to be providing correct voltage to coil - I'm getting funny behavior from some of the gauges in instrument cluster - this symptom may have an unrelated cause. Would anyone have any suggestion for where I can find factory ohm ratings for instruments on my '41 as well?

Best Regards, Paul Lenker

40 Coupe

07-14-2014 @ 4:32 PM

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The original Ford resistor is 0.5 Ohm

TomO

07-15-2014 @ 9:21 AM

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The dash gauges have a resistance reading around .01 ohms. This is the reading across the heating element that bends the bi-metal strip that move the needle.

The erratic behavior may be due to grounding issues or a bad ignition switch. If you could provide more details about your car and its problems, we could probably provide more assistance in solving them.

Is your car still 6 volts, POS grnd? Are you using a stock coil, an aftermarket coil or a rebuilt coils? What voltage are you seeing at the primary connection of the coil? Do you have a good spark at idle?

Tom

This message was edited by TomO on 7-15-14 @ 9:23 AM

plenker

07-17-2014 @ 12:19 PM

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Thanks for your reply! It'll go into the calculus of making my old car perform better.

Best Regards, Paul Lenker

plenker

07-17-2014 @ 12:24 PM

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You ask good questions: the car is still 6v / pos ground;
the coil is a replacement bot from Bob Drake- but until the resistor problem was identified all the voltage we were getting at the coil was 2v - now after we replaced the "new" resistor with the "blower" resister we're getting a good 4v. the spark at idle now is good. we checked the voltage thru the ignition switch and there was no voltage drop. Your input is appreciated!

Best Regards, Paul Lenker

TomO

07-18-2014 @ 6:52 AM

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Paul,

Have you given any thought to the idea that the Drake coil mat be drawing too much current and dropping the voltage? The primary resistance should be 1.0-1.3 ohms from the ignition switch to the primary of the coil. If you have that, the coil may have a higher resistance than normal or your points have a resistance to ground.

To check the point resistance, remove the coil and measure from the coil contact to battery ground. It should be less than 1/10 of an ohm after the test lead resistance is taken into account.

The high current draw is the only reason that I can see that the resister is causing problems with the gauges.

Tom

This message was edited by TomO on 7-18-14 @ 7:15 AM

plenker

07-18-2014 @ 2:54 PM

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Good points - I have a helper with this matter and I will see if he has considered those items and check those readings. One problem we discovered was the coil I had on the car when these problems developed was a rebuilt coil from Skip Haney. When my helper discovered the low spark to the plugs, he suggested we try a new coil; so we replaced the Skip Haney coil with the Drake coil (which I had substituted earlier when similar issues occurred and I had replaced the Drake for the Haney coil) and then, when we recently reversed the switch, Drake coil produced the much stronger spark. Sounds confusing - suffice it to say - we've done a fair amount of switching / checking.
Thank you! Paul

Best Regards, Paul Lenker

supereal

07-22-2014 @ 2:38 PM

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Because of the fact that the primary and secondary winding of a Ford coil are connected, attaching the wires "backward" will reduce spark intensity considerably. If your coil is not marked, and your spark is poor, swap the connections and it will likely restore the spark power.

This message was edited by supereal on 7-22-14 @ 2:39 PM

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