starting problem

[classic car repair]

I have a 1938 Ford Pickup with the flathead v8, it been setting inside of a building for about 25 year, I got it running, start up with no problem, Now if I run the engine to get it warm up to about 160 deg, turn of the engine and retry to start it, it will not start, it will turn over ok, new carb, new condenser, have 2.1 volt to the coil, or 7.8 ohm, When it cool down, it will restart with no problem, run very good, you hit the button and it start right up, but hot engine it will not restart, can it be a coil problem? Thank You


started the truck up today, run it about 160 deg, was running good, step on the gas and it die out, try to restart, no start, jump the ignition resistor under the dash, and it started up, but it tested the wire going to the coil and it show 6.8 volt off the coil but can it drop on volts from the resistor when turning the engine over? So do I have a bad Resistor?

[deuce_roadster]

I don't think the coil will make a spark with less than 4 volts.
Call Chris Olsen at Bauer Electronics in Bend Oregon for a concours correct wiring harness.
Problem could be resistor or switch contacts also.

[Lawson Cox]

Call Skip Haney to rebuild your coil. Nobody else but Tyree Harris, 804-556-5200. for concourse correct wiring harnesses.

[slowforty]

Try jumping the ignition resistor. I had an issue with my car and found out it was the resistor. The resistor would not completely and it was hard to figure out the issue.

[Flathead Fever]

I don't think this is a fuel problem, but you never know what kind of new weird problem can happen. I keep seeing new ways for things to break that I didn't think was possible. Like the 12 beers bottle caps I just found in the gas tank of my dad's 32 roadster. Been in their since he bought the car over 20-years ago. That was a new one for me. I've never seen a shop manual that said check for beer bottle caps in gas tank.

At work, on a no start, the first thing I did was squirt some starting fluid, brake clean or carb cleaner into the carb. whichever can was closest to me. If it started it was a fuel problem and if didn't it was electrical. Unless something really bad had happened to the internals but those don't repair themselves when they cool down. That's the fastest test to determine which direction you need to go, fuel or electrical. Next you pull a plug wire and check for spark and the quality of the spark. A little spark might not be able to ignite the fuel mixture. You "do not" pull a wire and check for spark if you have an electronic ignition. You can damage them. You need to use a special test plug clamped to a ground.

It is strange that when you turn it off it won't restart. I could see the coil failing and quitting while it was running. But to repeat the same failure exactly the same way each time, just by turning off the switch is a little weird. You can top on electrical components while the engine is running and see if they fail but wouldn't tap on an Early Ford coil. With intermittent problems on modern engines that have all kinds of electronics they tell you do a "hot soak" to try and duplicate the failure. That seems to be what is automatically happening to you. Normally you get the engine up to operating temperature and then turn it off with the hood closed and let it sit a bit. Without the fan circulating air the engine components will adsorb heat from the hot engine. You can also heat parts with a heat gun that you suspect are faulty. That is exactly what you're doing when you turn off the engine, the temperature under the hood rises but that should take a while. If you're shutting it off and it immediately will not start, that's different. Just because the condenser is new doesn't mean it's okay. I used to get faulty new ones out of the box at workl. The old coils, even new originals in the Ford boxes can have the internal insulation breakdown after all of these years and then go open or short out with temperature changes. If you have an infrared thermometer, you could check the coil's temp while it's running at 160 degrees and then after a hot soak with the engine off and the hood closed. Is the coil getting hotter after the engine is shut down and then failing until it cools down, maybe. It's all guessing without test equipment. I have a Sun scope here at home so I can see the firing voltages.

Most electrical problems can be solved with a voltmeter, I hate to see people guess and then waste money buying parts that do not fix the problem. Sometimes, the real tuff intermittent electrical failures can only be solved by installing a known good part. On really weird problems at the fleet I worked on, like a suspect computer I switched the computer with an identical vehicle without telling the drivers. If a week later the guy with the suspect computer showed up at the garage with the same intermittent problem, I knew the computer was the problem. That was better than buying a $1000.00 computer and then have it not fix the problem. We don't have that luxury at home unless you have a fleet of 400 flatheads. You are lucky in that your problem is not intermittent, it can be duplicated, and it stays broke long enough to get a voltmeter on it and run some tests.

Does it have spark when it's not starting? What does the spark look like when it's cold compared to when it's hot

You can't check voltage to the coil with the points closed otherwise you are doing a voltage drop test instead of checking for available voltage. Disconnect the wire from the coil and then check its voltage. If the voltage is too low, you have excessive resistance in the circuit. If it's okay, then the problem is in the distributor and is most likely the coil.

[ford38v8]

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2.1v to the coil won't start your engine. Check your voltage drop from the battery through the ignition switch. If a drop, isolate it by putting your voltmeter on the in side of the switch and compare to the out side of the switch. You can dismantle the switch for a cheap rebuild, or get an NOS switch. Check the resistor's connections also. You want to get close to 4v at the coil, almost not going to happen, but you can feel good with 3.5v.

[Seth Swoboda]

I agree with what a few other folks have said. You coil and/or resistor is suspect. Your not going to start with that low of voltage. 3.5-4 is ideal.

[classic car repair]

started the truck up, run it to about 160 deg, was running good, step on the gas and it die out, try to restart, no start, jump the ignition resistor under the dash, and it started up, but it tested the wire going to the coil and it show 6.8 volt off the coil but can it drop on volts from the resistor when turning the engine over? So do I have a bad Resistor?

[ford38v8]

Your 6.8 v at the coil would have been with the points open, as the resistor needs a closed circuit to do it’s thing. To drop to 2.1 from 6.8 indicates an issue with your connections, as when it warms up, a poor connection will offer increased resistance. Resistors seldom go bad, but as long as you’ll need to work on that connection anyway, save yourself the extra work and replace the resistor with an NOS unit, never a repop. Clean up your connections, adding a little grease to prevent future corrosion resistance.

[Ken/Alabama]

Clean the contacts in the ignition switch along with all the other suggestions.

[TJ]

How old is ALL the wiring?