| fordmerc | -- 10-28-2018 @ 1:10 PM |
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'39 stalls when hot: while driving slowly, when I stop; also if I idle car to 3/4H temp and shut it off it ewill not re-start. Under each circumstance if will re-start within 5 min or so. Good spark, wire to plug when engine cold, but NO spark when I can't re-start it. Voltages at coil seem OK when cold. I have tried new condenser, two rebuilt coils,recheck rebuilt distributor - all test OK and nothing helped. What am I missing?
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| MG | -- 10-28-2018 @ 1:59 PM |
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Given your description, it does sound like an electrical issue to me. If you can, replace the coil and condenser with a known working coil and condenser - one at a time and not both at the same time....
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| trjford8 | -- 10-28-2018 @ 2:24 PM |
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Your '39 has the ignition resistor behind the dash and mounted to the firewall. You have the classic symptom of a bad resistor. It breaks down when they get hot.
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| trjford8 | -- 10-28-2018 @ 2:24 PM |
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Your '39 has the ignition resistor behind the dash and mounted to the firewall. You have the classic symptom of a bad resistor. It breaks down when they get hot.
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| MG | -- 10-28-2018 @ 3:00 PM |
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GOOD CALL, trgford8. I forgot about the ignition resistor under the dash.... This message was edited by MG on 10-28-18 @ 3:00 PM
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| juergen | -- 10-29-2018 @ 5:56 AM |
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Which is why he should check the voltage to the coil when hot. And if it is there, check if the spark is gone or weak (red versus blue). Or first just jumper the resistor when it stops running to see if it cures the problem. This message was edited by juergen on 10-29-18 @ 6:02 AM
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| fordmerc | -- 10-29-2018 @ 11:35 AM |
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I had done the swaps one at a time. I installed new resistor; no benefit; problem remains. Voltage at coil with new resistor is 1.85 (it was 3.5 with he old one) cold After car stalled again, and while hot, voltage same = 1.85 I caught the spark as the car was sputtering to a stop and noted that the spark (wire to plug) became weak and then ceased as engine stopped. No spark as engine turned over with starter then. I did this before reading juergen's post, but I did check voltage at the end of the resistor when hot and stalled and it was 1.85 (as when cold). After my head stops hurting from banging it against the wall, I will try the resistor bypass, but it seems that voltages suggest that it is working as expected both hot and cold.
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| trjford8 | -- 10-29-2018 @ 4:33 PM |
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As I recall the voltage to the coil after it passes through the resistor should be 3to3.5 volts. The voltage you are getting is not enough. If you had 3.5 volts to the coil with the old resistor why did you change it? Was the old resistor breaking down when it got hot and not giving enough voltage to the coil? Who rebuilt the coil? I still tend to return to the resistor as the problem. Do the jumper trick with a wire that bypasses the resistor. You can do it with a wire that has two alligator clips. Do it as soon as the car stops. If it fires right up it's the resistor.
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| JayChicago | -- 10-29-2018 @ 9:16 PM |
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Here is my take on this: I agree that 1.85 volts at the coil is too low, suspect that new resistor is not good or wire connections are not tight. If you were getting 3.5 volts with the old resistor, I would reinstall that one. A new resistor made cheaply may be bad. The old resistors are robust, don't fail often, and don't vary from hot to cold. (the resistor is designed to run hot; you can burn your fingers on it within a minute) Your symptoms seem to me to be the classic, common, coil failure. Shows itself when coil gets warm, then functions again when coil cools. But you have tried two different rebuilt coils, so that stumps me. Did they not get rebuilt properly? Did the ignition switch get left on for an extended period of time and cook the coil ? I think at this point you should replace the resistor to try to get good voltage to the coil. With battery voltage at 6.0-6.5 volts, you should see 2.5 to 3.0 volts at the coil with engine stopped. This should then jump up to around 3.5 volts when engine is running and points are open 20% of the time. (during points-open, no current flow=no voltage reduction thru the resistor) Good luck. Keep coming back when you can. We would like to learn how this mystery gets resolved.
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| dandy32 | -- 10-30-2018 @ 2:39 AM |
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I had A problem like this and it turned out my point gap was alittle to wide. started fine and ran good but as it got warmer the point gap would open up just that little bit and it would start to stumble and eventually die wait 5-10 minutes and it would start and do it all over again.closed them up A bit and its still running fine after 4 years . IMHO
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| TomO | -- 10-31-2018 @ 6:33 AM |
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I agree with going back to the resister that gave you 3+volts. You should have this voltage hot or cold. I would start with measuring the input to the coil when the engine has been running for a while. If it is low, check the voltage at the ignition switch, if it is OK, check the point dwell with an analog (one with a needle) dwell meter. It should be between 34 and 36 degrees. If it is longer have the points checked for pits and timed on a distributor machine. Tom
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| fordmerc | -- 10-31-2018 @ 11:11 AM |
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Follow-up: While I muddy my waters daily, today I noted that after running a while, I shut engine off, wouldn’t restart (same as past) No voltage anywhere! Next step is to check the ignition switch. In review, the coils tried were both rebuilt by a highly acclaimed re-builder in Florida, and he rechecked one last month. The resistors used were the original 1939, a repro first installed 3-5 years ago, and a new one that really doesn’t look right anyway. Today I used the middle one that was working until the onset of troubles. Only one new condenser has been tried. Voltages at start of the day were batt=6.2, at coil= 2.7. My multimeter is unreadable at the coil when the engine is running. I will report ignition switch testing as soon as I can. Thanks for all comments and help.
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| GPJohnson | -- 10-31-2018 @ 12:32 PM |
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I'm having the same problems on my 1946 Business Coupe. I've put in new spark plugs, points, condenser and coil. It ran fine for a while and began stalling again. I have to wait for quite a long period of time for it to cool down before if will start up. Will appreciate any thoughts!
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| JayChicago | -- 10-31-2018 @ 7:29 PM |
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GPJohnson One thought comes to mind: You say you have a new coil. Is it actually new, not rebuilt? I have read on the forum that new coils from the usual vendors may not be made well internally, are not reliable or don't last long. Most forum posts recommend having your coil rebuilt by Skip Haney in Florida. I never heard of a problem with one of his coils. He has an ad running in the V8 Times. When I was experiencing the classic bad coil problem, I had to wait about 30 minutes with hood open for the coil to cool.
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| TomO | -- 11-01-2018 @ 7:38 AM |
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Fordmerc, You should always try to trouble shoot the problem when it is in the failing mode. Some things, like a weak spark that disappears when hot, can be determined when the car is running OK. To check your ignition switch when the car is running OK, you can try vibrating the switch by rapping on the case when you have a voltmeter connected to the coil terminal of the switch. You can also try switching on and off, while watching the voltage to see if it varies from one time to the next. To clarify my previous post: You can check the voltage at the coil after shutting off the ignition switch and then turning it back on without starting the engine. Excessive dwell can cause the coil to overheat and fail. Analog dwell meters can be connected at the terminal on the coil, where the condenser mounts. I do not recommend digital dwell meters as they are too sensitive for these cars. Analog volt meters are also more useful in trouble shooting these types of problems. Digital meters are great for checking for circuit resistance and voltage drop. Tom
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| TomO | -- 11-01-2018 @ 7:51 AM |
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GPJohnson, I recommend that you start a new post with your symptoms and what you have done to fix it. While checking for an ignition problem is very similar on all cars, the difference in hardware may change the check points. A new post will reduce the confusion of which problem the response pertains to. You did not say where you got the coil, whether it has an internal or external resister and what other modifications have been made to your car. Tom
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