| JayChicago | -- 09-02-2016 @ 7:32 AM |
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40 Ford, all stock I have read on this and other forums that you need 3+ volts at the coil primary terminal to get proper performance out of the ignition system. Is that to be measured with engine running or stopped?
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| ken ct. | -- 09-02-2016 @ 7:57 AM |
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It can be measured with the motor stopped but will depend wether the points are open or closed. Will either be 3+ or 6+ depending. ken ct.
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| JayChicago | -- 09-02-2016 @ 8:03 PM |
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I get distinctly different voltage readings at the coil depending if engine is running or stopped. But I have never heard that mentioned in discussions, just that I need 3+volts at the coil. I am reading 3.6 volts engine running, but only 2.7 volts engine stopped. So my question is: is this normal?
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| GK1918 | -- 09-03-2016 @ 12:31 AM |
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For years this has baffled-ed me why Ford used a resistor to drop coil voltage? I can see that for 12vt. My reason is I grew up with a ration of Plymouths Dodges of the 1930's 40's 50's and Jeeps, trucks, buses and none use a resistor. I have worked on many intercity buses of the 1940's that were 12 volts again none used a resistor. And then I have several F6's and several F8's 6volt pos grd. again no resistor. Only thing I can think of is that maybe something to do with duel points used up till 1948? I don't use a resistor so I get 6vts at the coil and I don't see any problem. sam
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| TomO | -- 09-03-2016 @ 7:48 AM |
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Jay, Your readings are in the normal range, but slightly on the low side. Check the voltage going to the ignition resister, it should be at least 6.2 volts with the engine stopped. If it is lower, check the battery voltage. If the battery voltage is more than 0.1 higher than the input to the resister, you have excessive resistance in the circuit. To find the point of resistance, turn on the ignition switch and tap the starter until the points are closed , connect the COM lead of your meter to the NEG post of the battery and probe the connection points with the + lead of your meter. Turn off the ignition switch and let the coil coll between probe points. Tom
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| ford38v8 | -- 09-03-2016 @ 9:07 AM |
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Jay, as Tom says, your readings are low. The difference between the two readings reflect the state of charge on the battery alone, against the output of the generator while running. Alan
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| JayChicago | -- 09-03-2016 @ 1:37 PM |
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Tom and Allan Thanks. I have done the voltage drop tests, following the procedure posted by Tom in the past. I am getting .2 volt drop to the resistor, .1 to the switch, and another .1 thru the switch to the resistor. But I would think those tenths of a volt are almost negligible compared to the 3.2 volt drop I am getting across the resistor. (with engine stopped, battery voltage reading 6.1 volt)
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| pauls39coupe | -- 09-04-2016 @ 9:46 AM |
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Disconnect the wire at the coil and run your volt meter from the wire to a ground. You should see near battery voltage. If not your resister may be bad. Replace it with one correct for your year and model Ford. Voltage readings with the wire connected should be between 3 and 6 volts, depending on if the points are open or closed. Getting an accurate reading with the engine running is nearly impossible, especially with a digital volt meter. My cheap analog meter will hover around 3 volts with the engine running. The resister is a ballast resister which increases resistance as it heats up. You may see the darn things actually glow. The purpose is to level the voltage to the coil as the generator produces higher voltage, thus saving the coil. If the engine is off, and the coil disconnected you will see very little voltage drop across the resister. Many modern round can coils have an internal resister, thus they don't need the resister Ford used under the dash. I suspect this may have been the case with the early cars another poster mentioned. Clean up all your connections take the ignition switch apart, to lower voltage drop between connections.
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| JayChicago | -- 09-04-2016 @ 1:33 PM |
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Thanks for your input Paul "Disconnect the wire at the coil and run your volt meter from the wire to a ground. You should see near battery voltage. If not your resister may be bad." I believe this test will not test resistance in the circuit, you will always see full battery voltage this way. Resistance will only show itself with current running thru the circuit. "The resister is a ballast resister which increases resistance as it heats up. You may see the darn things actually glow." Yes, this is what I have discovered the hard way, did not see mentioned before. I have checked 6 different resistors the past few weeks: my original, an Eichlin replacement, and four used originals from VanPelt. On the bench they all measure .4 ohms, which theoretically should produce a voltage drop of 2 volts. (V=A x R) But on the car, with +/-5 amps running thru them and getting hot, they all produced a 3.0 to 3.4 voltage drop. This leads me to believe the resistance value of the ballast resistor is increasing about 50% when hot. I'm not an electronics engineer...would love to hear from someone if I am all wet, if I am missing something here.
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| pauls39coupe | -- 09-05-2016 @ 1:59 PM |
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Jay, Back to your original questions, in my experience this is normal. As Ken said 3 to 6+ volt depending on the points being open or closed with the engine stopped. Checking the voltage at the coil with the wire disconnected will tell you if the resister has failed (broken) or if there may be a problem down stream. It would be interesting to hear a electrical engineer weigh in on the subject. Are you having drivability or starting issues? Or just curious about the voltage values?
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| JayChicago | -- 09-05-2016 @ 9:44 PM |
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Paul Thanks for your advice. I have an intermittent miss at cruise speed/steady throttle. Engine pulls strong under acceleration, which made me doubt a weak spark condition. Nevertheless, I did start the trouble shooting with the ignition system, found 2.7 volts at the coil, and found that is the result of a 3.2 volt drop across the resistor itself. I've spent the last three weeks trying to find a better resistor, six so far all produce greater than 3 volt drop. And I've spent a lot of time second-guessing myself, double-checking with three different multi-meters, wondering what I am doing wrong.
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| pauls39coupe | -- 09-06-2016 @ 8:49 AM |
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Jay Chasing an intermittent problem can drive you nuts. Assuming that you have checked the points, changed the condenser, have a known good coil, the ignition switch is bright and shiney inside, and there are no loose or broken wires, it may be time to look elsewhere. Using a good vacuum gage should point out sticking valves or weak or broken springs. I had a similar problem a couple of years ago which turned out to be debris in the carburetor. It held enough fuel to fill the accelerator pump, and the power valve opened Ok under load, but it had a occasional miss during cruise. The main jets were partially plugged. Check the color of your spark plugs after a steady drive. If they are white, you may be on to something. Try pulling the choke out partially, this will richen the mixture and may stop the miss. If it does, look to a carb problem. Let us know what you find.
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| village grande | -- 09-06-2016 @ 4:54 PM |
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Jay I have the thread about a coil problem running along with yours and they seem to have a lot in common. I'm also experiencing a miss or stumble at a steady cruising speed in any gear. The car starts and runs fine except for this annoying glitch. I've covered a lot of ground checking compression, rebuilding carburetor, checking ign. wires, points, plugs, cap and rotor, dwell and new coil and condenser, also did vacuum test- steady 20 inches. Will follow suggestions from other members on my thread and try a new condenser listed at .21 to .25 mfd. will also check wire from coil to dist. This problem is not noticeable until the engine warms up, maybe 10 minutes or so. Do these symptoms sound similar to yours? Village Grande--Bill
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| carcrazy | -- 09-06-2016 @ 7:58 PM |
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This is most likely an ignition problem. Do you have the original type of coil mounted on top of the distributor or the tubular type of coil used with an adapter? I have had problems with the adapters where the spring loaded contact jammed in the adapter housing and only made intermittent contact with the rotor. If you are using resistance core spark plug wires, check their resistance when they are warm.
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| JayChicago | -- 09-06-2016 @ 10:03 PM |
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Paul Thanks for those ideas. One of the evil things about this intermittent miss is I cannot get the miss to occur under no load in the garage/driveway. Hard to trouble-shoot while cruising down the road. My new spark plugs are very black, leading me to think it is an over-rich condition, or non-firing spark condition. Or as I suspect, both! I tried to tackle ignition first, but am now stumped by the inability to get 3 volts to the coil because the voltage drop across every resistor is more than 3 volts. Sure would like to hear advice on that from someone.
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| JayChicago | -- 09-06-2016 @ 10:45 PM |
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Bill I've been following your thread. Yes, your symptoms do sound similar to mine. My miss is noticeable right away, but gets worse with a warm engine. I will be sure to post on here if I discover anything significant. Please do the same for me. Re condenser: I've been told and read that you cannot trust a brand new condenser to work, that when tested most do not meet spec, and some don't function at all. And how would you know? Who has the ability to measure a condenser's capacitance in microfarads? So I paid a premium for a new condenser from Bubba's. Don't know if it is any better, I have no way to test it, but I bought his sales pitch: www.bubbasignition.com/condensors.html This message was edited by JayChicago on 9-6-16 @ 11:08 PM
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| JayChicago | -- 09-06-2016 @ 11:03 PM |
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CarCrazy I have the original style coil. The car came to me with the classic coil problem, no-start when warm. Now it has a freshly rewound coil by Skip Haney and that problem is history. But sorry to say, the new coil and condenser didn't solve the miss problem. Good idea to check the spark plug leads. I will do that. They appear to be new, and I believe they are solid conductors because they are stiff and there is nothing printed on the outside insulation.
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