too low voltage at the coil terminals

[ThomasBorchers]

Hi!

 

It will not end with our 1947 Lincoln. Still the thing with the ignition.

 

I got back the coil rebuild by Skip. Put it in, no spark. Removed the coil, distributor, checked if the points have good contact and yes, they have. Put all in place.. suddenly I had spark. Engine started but had a rough idle and after running the engine a bit, some plug were wet. But they are old, were often wet since we have the ignition problem. Together with really old ( 2 years ) gas, this can’t work. I ordered new plugs and I am waiting for it.

 

In the meantime I checked the voltage at the coil terminal as Skip wrote in his facts sheet which came with the coil. Fully charged new battery which has 6.36 volts. I checked the voltage at the coil. Ignition on, one point set is closed, one open. On the closed side: 2.2 volts ( where it should has around 4 ) and with open points just above 6 Volts. Ground from Battery goes directly on the engine.

So Skip told me to make some other tests link a jumper cable at the ignition switch, put the resistors ( have correct one ohm resistance ) at the coil terminals and take current directly from the battery. And at least I removed the resistor out of my 1968 Mercedes which has 0.9 ohms and hooked it at the coil but at all these tests… I have just 2.2 Volts at the coil. The distributor is an overhauled one, bought at George Trickett if I remember right in 2005. New condensors.

 

I have found an old topic in the AACA forum written by me. Already in 2004 I had the problem with the low voltage and bought then this “new” distributor and coil and the car run then. But not really good. So actually I am still at the point of 2004…

 

I am out of ideas, and I am afraid that Skip will give up in the future. He said in the last mail, that I should try to let the engine run without the resistors but just a short time to see how it runs then.

 

Kind regards

 

Tom

[19tom40]

When the car sits for a long time, the points will develop a thin film of corrosion. That is probably is your first scenario, were you did not have spark and then you did have spark.

 

The ballast resisters will increase their resistance as they get hot. To determine where your problem may be, check the voltage across the resister. Connect the black lead to the source voltage terminal on the resister and the red lead to the terminal going to the coil that has the points closed. Turn on the ignition switch. The meter should read no more than 2.2V. Repeat the test at the other resister after tapping the starter to close the other set of points.

 

If the meter reads higher, the resister has probably developed some corrosion where it is riveted to the case or there is corrosion under the connectors. I have used electronic cleaner to reduce the corrosion at the rivets. I then coat them with a thin film of ignition grease.

 

If the meter reads 1.8-2.2V the resister is OK and the problem is elsewhere. Check across the ignition switch in the same manner, the meter should read 0.1V or less.

[ThomasBorchers]

Hi Tom,

 

 

thanks for your answer.

 

 

Yes, I often had this with the contacts. Recently at my Model which ran not for 4 months or so.

 

 

I did as you said and here are the results: Between the terminals at the resisters with points closed I read 3mV ( millivolts ) each. Between the two terminals at the ignition switch with switch pulled, I read 30mV. But the 3mV is much less at you said.

 

 

Some days before I removed the resisters to contact them directly to the coil as Skip said. So this was the chance to clean up all contact surfaces at the wires and at the resisters. I used also some “tuner spray” for a good contact which I have for my vintage hifi receiver.  But now the resisters are on the old spot under the dashboard again.

 

 

Kind regards

 

 

Tom  

Edited May 24, 2022 by ThomasBorchers (see edit history)

[19tom40]

A reading of 3mv tells me that NO current is flowing in the circuit or you do not have the meter connected properly.

[ThomasBorchers]

Hi Tom,

 

yes, this is the way I put on the leads of the voltmeter. Perhaps I am wrong but…. I pick up so current from two terminals which have the same polarity. In this case from minus to minus. So it is in line. In line I can check the ampere and resistance but for voltage I need plus and minus. So for my understanding to check how much voltage flow, I have to put one lead at the outlet terminal of a resistor and the other one to ground. Or?

 

Kind regards

 

Tom

[edinmass]

Do yourself a favor........isolate the distributor from the car. Just jump power and ground wires and see what you get. Battery switches, ignition switches, bad grounds, resistor issues, just remove everything from the list of possibilities. Ignition troubles are not rocket science, but if you have little to no experience dealing with pre war cars.........you're doing yourself a disservice. A skilled mechanic should be able to figure out the issue in less than half an hour. Start with the simple things first........Use a battery and jumper leads to get the car started........go from there. 

[ThomasBorchers]

Hi Edinmass,

 

thank you for your answer.

I already put direct the resistors on the coil ( I even tried a resistor where I know that it works on an other car ), put direct current with two leads from the battery to the resistors terminals and also put additional ground to the distributor. Cleaned all contact surfaces. So everything was already total isolated to eliminate problems of switches and leads.

Well, I have just a little bit experiences in old cars… just 27 years of working at classic cars from 1901 to the 70s.😉 But sometimes… I repaired lots of ignition problems of lots of different cars but the Lincoln tells me who the master is in this game. At the moment...

The only thing I can imagine would could be the problem is a bad contact between the ignition contacts under load.

 

I have just checked it again, with cold resistors I have now 2.7 volts at the coil with closed contacts.

 

 

Tom

Edited May 24, 2022 by ThomasBorchers (see edit history)

[Ray500]

Measuring the voltage across the resistors tells you the drop you should expect on the distributor connection.  Of course start with clean connections everywhere you can from the battery to the distributor terminals.  Ignition switches can be a problem at times.  The most important voltage measurement is from ground (positive) to the terminal that comes from the under dash resistors.  If it's below 2.5 volts (points closed)  need to trace it backwards toward the battery.  Yes, you can hook up the distributor without the resistors, but if you leave it that way you'll fry the coils eventually.  For a short period it should be fine to get things running.  You need clean tight terminals to insure the proper flow of current.  I also use a little clear silicon grease on terminals once things are working correctly to keep corrosion down.  

[edinmass]

Tom………take a look at the points where they pivot on the post. I have seen intermittent arcing from bad/defective/thin insulators that cause crazy and intermittent no spark. Pull all the plugs, and shutoff all the lights, and crank the car over while looking at the distributor. Look for arcing. You can do this with the condensers disconnected also. Send me a photo of the distributor……..If it will fit on my Sun Distributor machine I will run it/set it up for you no charge……….you could also have some weird problem like parts missing, bad ground (I know you said you ran a ground wire.) At this point, I would get a parts diagram, and disassemble the entire thing and do a parts check on it……….strange things happen to distributors over the years……….after having such strange issues with what is a basic and simple set up I have found most of the time it isn’t the mechanic………..it’s some crazy unpredictable and unseeable issue that is causing the problem. How about a few photos…….

[ThomasBorchers]

Hi Ray, hi Edinmass,

 

at first: Thank you for your thoughts and help. And Edinmass especially for the offer to check my distributor. I can make some photos of the old one which I still have in my shelf. But perhaps it is a bit far away to send it to you.

 

Today I got the new spark plugs, filled in fresh gas and started. It started right up and runs good. The first try I had three wet plugs in one row on the right cylinder bank but at the second try now just one. I checked now with running engine the voltage at the coil and on the left terminal I have then 4.4 volts and right 4.7 volts. The bad thing is that the generator is not working… 😒

 

I don’t know if the voltage is with running engine now ok or still to less. What would you say?

 

Kind regards

 

Tom

[19tom40]

Glad that you have it running. The voltage at the coils with the engine running will be higher than when the engine is not running. Your generator is probably not charging because of slight corrosion on the cutout points in the Voltage regulator. Disconnect the battery and clean them or sometimes just driving the car will burn through the corrosion.

 

If you are still having the low voltage at the coil with the engine stopped, this can cause hard starting when hot. Check out the circuit using the procedure outlined below.

 

2.7V across the resister is slightly high, but not enough to give you a problem. We now know that the resisters are good enough to give you a good running car.

 

6.3-2.7 = 3.6 that you should see at the coil. You are losing about 1 volt in the rest of the system.

 

To find out where you are losing it, connect the black meter lead to the post of the circuit breaker that comes from the battery. It should have 2 heavy yellow wires and a yellow and black wire that goes to the ignition switch. Connect the red to the resister terminal that it was on for the resister test. Turn on the ignition switch. The meter should now read 2.7V - 2.8 V. If it reads higher, your ignition switch needs cleaning.

 

Disconnect the battery and operate the ignition switch many times to try to clean it. Reconnect the battery and repeat the test. If the voltage is good now, you are set to go. If it is not, you will have to disassemble the switch and clean it.

 

[ThomasBorchers]

Hi!

 

I find out something new today. I let the engine run and checked the spark at the ignition cables to ground. This was interesting. On the left side ( drivers side ) I have a really strong spark. On the right side… just a very small weak spark or even no one ( remember the wet plugs on the right side ). I know that the two parts of the distributor serves not just one side, I know that the cables go across. 3 on the same side, three to the other. So it can’t have to do something with the distributor because on the left side I have at all plugs a strong spark. For my understanding I must have a bad ground on the right cylinder head. Perhaps a good ground to the block, but not to the head. I will check this out and let you know.

 

Tom

[19tom40]

I would try replacing the condenser.

[ThomasBorchers]

I have now cleaned up the ground points at the right cylinderhead but it make to difference.

 

OK, Tom, where could I get a new set of resistors? I can't find them in the Internet. Do you have a source for me?

 

Kind regards

 

Tom

[ThomasBorchers]

At first to all: I am sorry for my confusion in this theme. I have here a construction side on my place with lots of dirt, noise and so on. Hard to find a clear though.

 

Today it is quit and I studied the wiring diagram of the Lincoln and now I understand how the ignition works and where I have to look for the problem.

 

I understand ( sides in driving direction ) that the right side of the coil with the resistor and condenser, and the part near to engine of the rotor, and the part near to engine of the distributor caps are working for the right side of the engine.

 

Since I hooked directly a cable to the coil terminals with no resistor, I should exclude that the problems come from a resistor or to less power to and from resistor to the coils.

 

Next step I did today was to change the ( new ) condensers from left to right. Ah! Suddenly I had good spark on the right side of the engine and bad or no one on the left side. This was a sign where the problem could be. So I took one of my old condensers. I checked the value of the new one: 0,55 micro farads. Hmm, then of the old one I still have: 0,55 micro farads. I put in the old one and then I had a really strong spark on both sides of the engine. Engine runs nice and smooth. So the new condenser was not ok.

 

So it seems, that the problem is solved. But it could be that my condensers have not the correct capacity. 0.55 mF is too high, or?  0.31 to 0.34 is probably correct?

 

Kind regards

 

Tom

Edited May 27, 2022 by ThomasBorchers (see edit history)

[Ken/Alabama]

The ignition switch is dirty . 

[ThomasBorchers]

No, this ist not the problem.