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Posted By Discussion Topic: stall when hot ?electrical? -- page: 1 2     fordmerc 10-28-2018 @ 1:10 PM reply profile send p.m. New Member Posts: 180 Joined: Oct 2009 '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? MG 10-28-2018 @ 1:59 PM reply profile send p.m. Senior Posts: 1261 Joined: Nov 2009 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.... trjford8 10-28-2018 @ 2:24 PM reply profile send p.m. Senior Posts: 4220 Joined: Oct 2009 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. trjford8 10-28-2018 @ 2:24 PM reply profile send p.m. Senior Posts: 4220 Joined: Oct 2009 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. MG 10-28-2018 @ 3:00 PM reply profile send p.m. Senior Posts: 1261 Joined: Nov 2009 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 juergen 10-29-2018 @ 5:56 AM reply profile send p.m. Member Posts: 258 Joined: Jan 2010 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 fordmerc 10-29-2018 @ 11:35 AM reply profile send p.m. New Member Posts: 180 Joined: Oct 2009 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. trjford8 10-29-2018 @ 4:33 PM reply profile send p.m. Senior Posts: 4220 Joined: Oct 2009 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. JayChicago 10-29-2018 @ 9:16 PM reply profile send p.m. Member Posts: 484 Joined: Jan 2016 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. dandy32 10-30-2018 @ 2:39 AM reply profile send p.m. New Member Posts: 102 Joined: Oct 2017 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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