I have a 79 RV with a 460, has 65,xxx miles. The problem is sometimes it starts and runs fine for about 15 to 20 min, then dies. sometimes it won't start at all warm or cold. It turns over fine, its getting fuel but no spark from the coil. When I put a jumper from the battery to the positive side of the coil it'll start and run fine, when I pull the jumper off sometimes it dies sometimes it continues to run. I've replaced the pick up coil, coil, icm, checked wiring and it all looks good. I've pulled the icm off and had it tested to make sure I didn't get a bad one. One thing I've noticed is the red and white wires are crossed on the D shaped plug at the icm, not sure if thats an issue though. Any ideas on what this could be before I throw a $20 ignition switch at it?

 

Does sound like the Ignition Switch.
You could use a test light to check.

 

how would I go about testing it?

 

1. If you do not have a 12 Volt test light then get one. (or make one)
2. Pull the "S" wire off the starter solenoid. (so the engine does not crank)
3. Turn the key on.
4. Put the ground clip of the test light on a good ground. (or clip it to the NEG post of the battery)
5. Touch the point to the BAT (+) side of the Ignition Coil. (it should light)
6. While holding it there have someone turn the key to the start position. (the light should get brighter.
7. Have them release the key. (the light should stay on but not as bright as in the start position)
8. Have them jiggle the key with out turning it. (the light should burn steady)

The test light:


The "S" wire term:




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Thanks for your help, after doing the test we figured the switch was bad. we bought and installed a new switch today and had the same problem. found the positive wire on the saddle connector was not always making contact after we fixed that it starts every time now but there is a new issue, it idles really high all the time. we checked the voltage to the coil and with the key in the run position without the engine running its around 7 volts, but once you start the engine it stays right around 11.5 volts. I'm pretty sure thats the reason for the high idle, but it never did this before. I tried swapping the old switch back in with the same result, any ideas?

 

Low voltage at the coil will not make the engine run at a high RPM.

Maybe its is stuck on the high idle cam on the carb.
Check for stuck choke or bent parts at the carb.
Check the high idle dash pot or solenoid also.

 

I'll check the carb out tomorrow, but just to be sure, with the engine running 11.5 volts on the positive side of the coil is ok?

 

Yes their is a voltage dropping resistance wire that does that in the run position. You have full battery voltage while cranking however.
This makes the coil last longer.

 

thanks, I'll check the carb out tomorrow and see if I can figure something out

 

everything checks out ok on the carb. the thing I don't get is with the key in the run position and the motor not running the coil is getting 7 volts on the + side, with the engine running the coil is getting 11.5 volts to the + side. What could cause the voltage to be higher when running?

 

Maybe it is not wired right at the Ignition plug.
I1 & I2 reversed.


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