304 starting quirk

C

chopperkarl

New member
Need help diagnosing a peculiar starting problem. The truck is a 73 Scout II w 304 and 4 speed manual. When I turn the key, the engine cranks but won't fire. When I release the key, it fires. It's tricky because, once the key is released, there is a very short amount of time for the engine to fire before running out of momentum. Any body have an idea what the issue is?
Thanks
-karl
 
The 12vdc primary ignition wire is burned out or shorted, which bypasses the ignition resistance wire during starting only.
 
Ok. I found a diagram in the manual that depicts the ignition resistor. Where on the truck is this normally located? Where do they sell the replacement you mentioned?
Thanks again!
 
Originally, your '73 Scout was fitted with a resistor/toaster wire of a specific length. The length is critical for achieving the correct amount of resistance. In this case, 72 inches of wire length provided 1.8 ohms of resistance. This wire runs between the engine side of the firewall bulk head connector and the positive terminal of your ignition coil, with the excess length doubled over on itself several times and then wrapped with electrical tape. If this wire is still present on your Scout and there is indeed an issue with it, your best option would be to replace the entire length of it with a piece of 16 gauge standard automotive wire. Then purchase a porcelain ballast resistor with 1.8 ohm resistance and interrupt your new wire run with the resistor.
 
chopperkarl said:
ok. I found a diagram in the manual that depicts the ignition resistor. Where on the truck is this normally located? Where do they sell the replacement you mentioned?
Thanks again!
Click to expand...

Re-read my response. The primary 12vdc wire is open or shorted. This wire gives your ignition the full 12 vdc during starting, and only with the key in the "start" position.

The resistance circuit is ok, as evidenced by the short bit of ignition as you release the key from the "start" position to the "run" position. Since the engine is not running, there isn't enough ignition to keep it going after going from "start" to "run" with no ignition in "start".

The other scenario (which you do not have): the engine starts then shuts down when the key is released from "start" to "run"....that is the resistance wire shorted out, or the resistor if you have one.
This is the more common situation and is also why many folks carry a spare resistor in their tool box or glove compartment.
 
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The resistor feed is actually the primary feed. The resistor bypass is just that. A bypass of the primary feed that is energized only during starter cranking. Even the term "bypass" is a bit of a misnomer in this case, as the primary (resisted) feed is also energized in ign start position as well as ign on. As such, it is certainly possible to start a well-tuned engine with a breaker points distributor in mild climates without the bypass circuit even in place. I've done it plenty of times. Now, if that bypass was present, but shorting to ground, that would be problematic, but I'd expect or at least hope this would trigger a fuse to blow early on. Perhaps not? At any rate, the op should also consider that he May have a problem with his column mounted ignition switch. Further diagnosis will reveal the culprit.
 
Guys,
I can't thank you enough. Solved the problem. I had the wire from starter to coil on the negative side of the coil, thus shorting the circuit. Truck fires right up now that its on the positive post. Now that I half understand the ignition circuit, I'm hoping you can help me finnish the lesson. I uploaded a diagram of what's under my hood. Three wires go into the firewall (each marked with "?"). I think I have 2 figured out, can you confirm? Thoughts on the last one?
Thanks
-karl
 

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