'41 V8 no start hot

[40cpe]

A friend of mine is working on a '41 for not starting when hot. He called me over for an opinion and this is what I found: Battery voltage 6.1 and it has 6.1 at the ignition switch and 5.9 at ignition when points are closed. Also 5.9V at hot side of resister w/points closed and 2.45 V on load side with points closed. 2.45 at coil when points closed. When it doesn't start I can jumper coil to battery and it starts.

The car runs well with little blowby. It has a new wiring harness, new coil (source unknown), new ballast resister, and new condenser. To our knowledge the distributor hasn't been rebuilt and it might be part of the problem because he cleans black soot off the plugs and lets it cool to restart. I think Batt voltage is a little low, and the voltage at the coil is a volt low.

If 2.5V at the coil is too low, is there a resister with less drop? Can the distributor draw excessive current to cause the low voltage?

I suggested a distributor rebuild by a professional because of the sooty plugs AND it runs hot /pukes water after a short drive (it's 95 degrees plus here). I'm thinking timing might be low, too. It has a rebuilt radiator, we don't see any bubbles in the radiator when running.

Sorry for the long post, but looking for input from those who have been there, done that.

[Veeder]

I'm fighting a similar but slightly different issue currently waiting to get some parts but a number of folks in this link give very helpful information in general regarding the 41 ignition system. Here is the link
Bob

https://www.fordbarn.com/forum/showthread.php?t=172608

[46ford]

6.1V is not a good battery. In my experience they are close to 7V no load. They don't last long these days.

[40cpe]

Thanks, Veeder. We just might go with the diode circuit, but we still don't know if the distributor is set correctly. I'll encourage him to send it for rebuild.

[40cpe]

Originally Posted by 46ford

6.1V is not a good battery. In my experience they are close to 7V no load. They don't last long these days.

I thought it should be about 6.5V and checked the charging voltage. 6.45V across the batt terminals was all it would put out at about 2000 rpm. I think it needs more charge.

This old car is not thrown together, most everything is new and looks professional. Of course, a lot of this new stuff isn't up to specs. I guess the resister/relay board under the dash came with the harness and makes me wonder if the resister is out of spec.

[DD931]

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This is a classic case of a bad coil. You say "source unknown". Not an indicator of reliability. Send it to Skip Haney in Florida for rebuild. He's the man. And replace the condenser while you're at it. If you decide to have the distributor rebuilt, many FordBarners go to Bubba's. Skip does distributor rbuilds also, I think. And, I think your resistor examination is a red herring. Good Luck! Let us know how it comes out.

[WestCoast]

you should have around 4 1/2 volts at the coil, generator should be putting out 7 1/2 volts

[40cpe]

Originally Posted by WestCoast

you should have around 4 1/2 volts at the coil,

Under what condition should I see the 4.5V? Engine off, ignition on, and points closed, or at coil with engine running?

[WestCoast]

you should have 4 1/2 volts to coil with key on, I use a ballast resister designed for 4 1/2 volts because it allows full voltage to coil when the key is first turned on to give a hotter spark to plugs, then it slowly goes back to 4 1/2 volts once its warmed up

[40cpe]

Thanks WestCoast, do you have a part number/supplier for the resister? This resister is in the stock location on the inside of the firewall. Does your part fit there? I'm asking because I'm not sure if the owner is a stickler for original.

[WestCoast]

if you have a Macs catalog they are on page 117, any old ford parts dealer will have them in stock, I don't have the parts number, mine is on the fire wall but mine is not all original

[40cpe]

OK, thanks

[40cpe]

I did some more checking today. Took the coil off to measure ohms. It is a Ford script coil and measures about 1 - 1.2 ohms. The meter floats a little. The resister measured .8 ohms, I understand spec is .35 ohms. Voltage at the coil reads 6.1V w/points open and 2.5V w/points closed with everything cold. I have a new echlin .35 ohm resister to be here tomorrow.

I hope somebody will correct me if I am wondering down the wrong path.

[Bluebell]

I don't think the resistor will be faulty (where it connects might be)
You need to make sure all the connections are clean and tight.
To sort of eliminate the charging side of things, can you try it on a fully charged battery? I would think you have high resistance somewhere to get that low voltage at the coil, but my first port of call would be to substitute that coil.
Have you checked out the ignition switch?

[40cpe]

The coil is new, Ford script, with correct (I assume) resistance of about 1 ohm. I don't know the source of the coil. The ignition switch is new and reads the same voltage (6.1) on both sides of the switch. New wiring harness. I've been through all connections. In fact, I get battery voltage (6.1) all the way to the coil terminal when the point are open. When I turn the engine to close the points the voltage goes to 2.5. I then went to the resister and had 5.9 going into the resister and 2.5 coming from it. That voltage drop in addition to the .8 ohm reading leads me to think it is the wrong resister. When the car warms up and doesn't start, I can jump the coil to the battery terminal and it starts fine. It has me thinking that a little more voltage will start it. I realize that the battery voltage is a little less than optimum, but surely these cars started with similar back in the day.