Extremely random, weak spark; sometimes no start

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cam.man67

cam.man67

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My Dart was running fine after the carb rebuild...for a couple weeks at least. Now it won't start!

Last drove I noticed a severe miss had started, but only at highway speeds and higher in the rev range. Got it home and now it wont start at all. Points look ok, and I can hear/occasionally see a weak spark, but not nearly not enough to start the car.

Hooked up an ohmmeter, my 1.5 ohm Pertronix FlameThrower coil reads 1.3 ohms. The .8ohm ballast resistor reads 1.2ohms.

Now here's where I'm confused. With the car off, At the battery I have 12.0v even. At the + side on the coil with the key on, it's 11.8, but randomly drops to 6.6. At the - side of the coil, its 11.6 but drops to 1.1v. The voltage at the points is identical to the numbers at the - terminal.

With the car running, I have 9.0v at the +, 5.7 at -. I'm going to take it out now and see if it misses, but it's idling fine presently in my driveway.
 
Doesn't the Pertronix FlameThrower have a module inside like the Accel Distributor. When my car wouldn't start I replaced the coil twice before I realized that it was the module. It had been giving trouble starting every now than then until one day it wouldn't start at all.

treblig
 
No, the Pertronix Flamethrower coil by itself is just a plain coil.

OP, the changes in voltage at coil + and coil - with the key on but not running indicate that the voltage supply to the coil and points is erratic, or that there is an erratic partial short around the distributor.

The supply side issues can be in the key switch, the connectors to it, the bulkhead connectors, the ballast being erratic (not so likely) or any where in the wiring from the key switch to the coil +.

The erratic short on the coil - side could be in the wire from coil to distributor (shorted or open) or the condensor.

Also, be sure that the points are not closed or closing when you do this test; the 6.6 and 1.1 volt readings at coil + and - are close to normal when the points are closed. So that test info could be OK, depending on how you made the test and if the points are closed or open. (I've seen this voltage look erratic if the points were just on the verge of closing and just breathing on them made them close or open.)

And your last running voltage readings at coil + and - look to be pretty normal. (I will guess you are using an analog meter....)
 
Have you checked the reluctor gap in the distributor??? .007" - .008" with brass feeler gauge...
 
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Points? OK then.

When the engine stopped, the key on, you have a percentage chance whether the points are open or closed

OPEN.............Either side of ballast, plus and minus side of coil should all read THE SAME.........exactly same as battery terminal voltage

POINTS CLOSED........Now the points are drawing current

"Switch" side of ballast should "in theory" read exactly same as battery terminals but often does not. If it is more than .3V difference (3/10 of one volt) you have problems in the switch/ harness / connections/ bulkhead connector etc

"Coil" side of ballast will vary with car to car, with ballast, and with coil. Should be between 6 and 10V or so "engine stopped"

Coil NEG......should be VERY LITTLE voltage, this depends on the condition of the points. If they are corroded, burned, worn, they will read more. If the car sits a lot they read more. I'll have to look, been so long///////I've forgotten the "maximum" value, I'm gonna say WAYYY less than 1/2 a volt
 
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Also do NOT leave the key in "run" with engine stopped for extended periods. If the engine stops with the points closed it will eventually ruin them.
 
krazykuda said:
Have you checked the reluctor gap in the distributor??? .007" - .008" with brass feeler gauge...
Click to expand...

He has breaker points I almost missed that. You should'a seen it.............LOL
 
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