Troubleshooting Ignition
Thread Starter
Intermediate
Joined: Jan 2003
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From: west chester pa
Troubleshooting Ignition
Hi Guys,
My '70 LS5 lost its spark, and I'm looking for a diagnostic procedure.
I'm getting different results when I check the voltage at the coil (positive terminal). First I got only about 6v, and the wire was getting warm to touch, then later I got the full 12v. But still no spark. So it seems like it could be an intermittent short somewhere.
I did replace the coil which didn't help.
Is there a step-by-step procedure listed somewhere to test the basics (what voltages should be present where, how to test coil, condensor, etc)?
Thanks, I appreciate any assistance.
John
My '70 LS5 lost its spark, and I'm looking for a diagnostic procedure.
I'm getting different results when I check the voltage at the coil (positive terminal). First I got only about 6v, and the wire was getting warm to touch, then later I got the full 12v. But still no spark. So it seems like it could be an intermittent short somewhere.
I did replace the coil which didn't help.
Is there a step-by-step procedure listed somewhere to test the basics (what voltages should be present where, how to test coil, condensor, etc)?
Thanks, I appreciate any assistance.
John
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
Of course there is. Here's a link that will allow you to test the parts with a DVOM (or a scope, if you have one): http://www.labscopes.com/pg06.htm If you're looking for something different, Google it.
It does sound like you have a current problem, though, since with the key on in the run position and the positive probe on the positive terminal and the comm to ground to measure voltage you should see 6-9v. You should only see 12v in the start position. But even with 12v in run, the car would still start and run fine but you'd burn up your points and condensor faster. It wouldn't affect the coil itself. I'd look at the condensor.
It does sound like you have a current problem, though, since with the key on in the run position and the positive probe on the positive terminal and the comm to ground to measure voltage you should see 6-9v. You should only see 12v in the start position. But even with 12v in run, the car would still start and run fine but you'd burn up your points and condensor faster. It wouldn't affect the coil itself. I'd look at the condensor.
Thread Starter
Intermediate
Joined: Jan 2003
Posts: 36
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From: west chester pa
You nailed it Gerry - I put a new condensor in and it fired right up. Thanks!
I had a few other questions -
- I also replaced the condensor attached to the coil bracket - what is the function of this, and is it as critical as the other one?
- If you get stranded due to a bad condensor (say it shorted out), can you get it running (enough to drive a few miles) by just disconnecting it?
- where is the resistor that lowers the coil voltage to less than battery voltage?
Once again, thanks for any assistance,
John
I had a few other questions -
- I also replaced the condensor attached to the coil bracket - what is the function of this, and is it as critical as the other one?
- If you get stranded due to a bad condensor (say it shorted out), can you get it running (enough to drive a few miles) by just disconnecting it?
- where is the resistor that lowers the coil voltage to less than battery voltage?
Once again, thanks for any assistance,
John
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
Originally Posted by jrs420454
- I also replaced the condensor attached to the coil bracket - what is the function of this, and is it as critical as the other one?
- If you get stranded due to a bad condensor (say it shorted out), can you get it running (enough to drive a few miles) by just disconnecting it?
- where is the resistor that lowers the coil voltage to less than battery voltage?
Once again, thanks for any assistance,
John
John
Thread Starter
Intermediate
Joined: Jan 2003
Posts: 36
Likes: 0
From: west chester pa
Originally Posted by gerry72
A:
Your welcome. Hardly anyone ever follows up or says thanks.
Your welcome. Hardly anyone ever follows up or says thanks.
Sorry to hear that - all I know is, guys like you all sure make life easier when these old cars act up once in a while.
John
