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faulty ignition switch?

J

jclays

Regular Contributor
Port side engine (350) fires and dies instantly when I release the ignition key. New ignition switch?
Also on occasion tachometer on the same engine will creep to higher RPM without the engine increasing in speed.
 
If your engine uses the ballast resistor type ignition set up, then there's no voltage going to the coil in the run position. Use a voltmeter to see if there voltage at the + coil post with the key in RUN position.


If there isn't, it's one of the following:

Bad switch
Bad connection in the run position
Burnt out ballast resistor
Broken or bad connection in the circuit.

Jeff
 
It should be 12V for Start/Crank off the solenoid, then OVolts on run.

Resistor wire should be 12V to resistor, then the other side powered, but Under 12V to run.
 
Will check it out today. What would make that side's engine tachometer climb without the engine's RPMs picking up. Just cruising and the tach's needle will climb then drop back
 
Yes, you could,,, But not a good idea, you might burn up your points, & condenser!

Just put the red wire from your test meter on the Pos + wire at the coil, and the black wire from the meter to any good ground, then put the ignition on RUN, and read what you got?

You should have under 12V, if there's no reading at all, your resistor is shot!
 
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Believe it or not, this JUST happened to me. Mr Port started right up, then died soon as I released the key--and several times over.

Knowing exactly what the problem was--bad ballast resistor--I got out my handy jumper wire and clipped it across the leads of the ballast resister to jump it out. Motor the fired right up ran fine on the way to the slip (and, no, it didn't burn up the coil--it was only for a few minutes).

Today I replaced what looked like a perfectly good ballast resister (only a year old) and the problem is gone. Tomorrow I go back to NAPA for a couple more, to go in my spare parts box.

Jeff
 
I have to agree with the bad ballast resistor idea.

Here's what occurs if this is an older ignition system:

During cranking, over-all available voltage is lower than what the ignition system normally requires.
During cranking, the ignition coil recieves full 12 volts via the "start-by-pass" circuit.

If the ballast resistor is faulty, when the key switch returns to "run", the coil (via the ballast resistor) is no longer recieving power.

This is likely why this engine fires up while the key switch is energizing the starter motor solenoid.


As for the tachometer..... I agree. Disconnect until the one issue is resolved.


Here's a rather crude schematic showing a typical start-by-pass circuit for the older systems.
 

Attachments

  • Ignition system w start by pass.jpg
    Ignition system w start by pass.jpg
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Went to the boat Sunday. With the key on the run position 12v going into the ballast, 7.95v going out and also at the coil....Hmmm..Turned the key the rest of the way to the start position and now the engine fires off and runs like a champ. Go figure.
 
jclays said:
Forgot to tell you not a points ignition. Older Prestolite distributors. Is the ballast still needed?
Click to expand...
This may depend on what the Prestolite uses for a triggering device, and what the ignition coil demands.
If Hall Effect triggering..... you may want to look up the schematic for this.

BTW.... since this failed on you prior.... you will want to find out why. I'd not trust that it will continue to work.
Could be a very small break in the ballast resistor coil that acts up intermittantly.


.
 
as cheap as the ballast resistor is, I would just replace that puppy. One problem eliminated and now you can move on knowing that is not the issue.
 
Agreed. The one that refused to run my motor (a year old) LOOKS perfect, but that sucker will not run the motor.

Jeff
 
kimcrwbr1 said:
Wouldnt you need a diode in the jumper wire from the start solenoid to keep power from backfeeding from the coil to the starter in the run position?
Click to expand...

If the starter motor's solenoid offers the "I" or "R" terminal, it is designed to not allow power feed-back.

If the solenoid does not have the "I" or "R" terminal, then perhaps his system uses a small four or five pin relay.
attachment.php
 
Replaced the Ballast yesterday. Still no go. Replaced the switch....Bingo. Works fine. Now to address the Tach. I'll start a new thread.
 
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