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Old 09-05-2010, 06:14 PM   #1
firefirefire90
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Default how to test spark?

Hey everyone, the younging is back asking some probably simple questions.. but there you go.

Anyway, I finally got around to working on my early 1930 Model A coupe. I found a 6v battery, rebuilt the carb, slapped in some new spark plugs(gapped them to .35), and now I cannot seem to get the car to start. She will turn over just fine but it just wont catch. I know I have air and fuel, but not spark. I had to bypass my ignition switch so I know that could be the culprit, so I just now ordered a new switch + keys to replace the old pop-out one. I was reading on a model T article that you can make the coil buzz as a test to see if it's working correctly? I'm guessing this means that you put a positive and negative current to it to see if it's working inside there. Please let me know about anything i should check over. Electrics on this "simple" car are not always so simple

Thank you,

-Nick
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Old 09-05-2010, 06:25 PM   #2
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Default Re: how to test spark?

and also when I try to adjust the lever to retard or advance the timing, nothing happens.

hope that helps!
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Old 09-05-2010, 06:34 PM   #3
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Default Re: how to test spark?

Sounds like it could be an ignition circuit problem. There are other possibilities as well.

Here are the instructions for testing the ignition circuit from the technical tips section of the MAFCA website. Cut and paste is easier than typing. Hopefully this will help you find the problem.

http://www.mafca.com/tqa_electrical.html

Here is a voltage check of the circuit:
Connect the (+) side of your volt meter to a good ground point on the engine or frame.
Touch the (-) probe to the passenger side terminal box wing nut. Read 6 volts.
Touch the probe to the driver side terminal box wing nut. Read 6 volts.
Touch the probe to the (-) terminal on coil. Read 6 volts.
Touch the probe to the (+) terminal on coil. Read 6 volts.
Place a piece of paper between the point contacts.
NOW TURN IGNITION KEY ON.
Touch the probe to the end of the points arm, read 6 volts.
Remove paper between points. Open and close points and look for spark each time points open, (no spark means bad condenser, replace condenser).
If points are sparking then disconnect the coil center (high tension wire) from the distributor cap (leave connected at distributor end). Place the free end of the coil wire about 1/8" from one of the engine head nuts. Crank the engine over with the ignition key on. There should be a bright blue arc from the coil wire to the nut (ground point). No arc means bad coil.
Having said all of that, there are several things to check for. New condensers can go bad and new coils can go bad. But I would first look for something that may be shorting the circuit or causing an open in the circuit. Some of the other things to check are: Bad Ammeter. If ammeter has open circuit, all voltage is lost to the coil. You probably burned the wiring up because of loose connections on the back of the ammeter, or missing rubber grommet through center of terminal box, causing the ignition cable to short against terminal box posts, causing large current draw to burn wires. Do not screw ignition cable into the distributor too far. It can short out if screwed in too far. Make sure all nuts on the terminal box posts are tight. Also the two rivets on the bottom distributor plate sometimes get loose (especially on the reproduction plate) and short out the bracket it attaches. - Les Andrews, 1998 Technical Director
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Old 09-05-2010, 06:38 PM   #4
marc hildebrant
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Default Re: how to test spark?

Nick,

Did you say you have a model T ? I thought that you talked about a buzz from the coil.

Marc
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Old 09-05-2010, 06:42 PM   #5
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Default Re: how to test spark?

Quote:
Originally Posted by MCHinson View Post
Sounds like it could be an ignition circuit problem. There are other possibilities as well.

Here are the instructions for testing the ignition circuit from the technical tips section of the MAFCA website. Cut and paste is easier than typing. Hopefully this will help you find the problem.

http://www.mafca.com/tqa_electrical.html

Here is a voltage check of the circuit:
Connect the (+) side of your volt meter to a good ground point on the engine or frame.
Touch the (-) probe to the passenger side terminal box wing nut. Read 6 volts.
Touch the probe to the driver side terminal box wing nut. Read 6 volts.
Touch the probe to the (-) terminal on coil. Read 6 volts.
Touch the probe to the (+) terminal on coil. Read 6 volts.
Place a piece of paper between the point contacts.
NOW TURN IGNITION KEY ON.
Touch the probe to the end of the points arm, read 6 volts.
Remove paper between points. Open and close points and look for spark each time points open, (no spark means bad condenser, replace condenser).
If points are sparking then disconnect the coil center (high tension wire) from the distributor cap (leave connected at distributor end). Place the free end of the coil wire about 1/8" from one of the engine head nuts. Crank the engine over with the ignition key on. There should be a bright blue arc from the coil wire to the nut (ground point). No arc means bad coil.
Having said all of that, there are several things to check for. New condensers can go bad and new coils can go bad. But I would first look for something that may be shorting the circuit or causing an open in the circuit. Some of the other things to check are: Bad Ammeter. If ammeter has open circuit, all voltage is lost to the coil. You probably burned the wiring up because of loose connections on the back of the ammeter, or missing rubber grommet through center of terminal box, causing the ignition cable to short against terminal box posts, causing large current draw to burn wires. Do not screw ignition cable into the distributor too far. It can short out if screwed in too far. Make sure all nuts on the terminal box posts are tight. Also the two rivets on the bottom distributor plate sometimes get loose (especially on the reproduction plate) and short out the bracket it attaches. - Les Andrews, 1998 Technical Director
I guess I'll have to wait on my new ignition switch to come in to test this! Thanks though!

Quote:
Originally Posted by marc hildebrant View Post
Nick,

Did you say you have a model T ? I thought that you talked about a buzz from the coil.

Marc
noo, I have a model A. I was just assuming that you could do the same with a model A coil? I might be wrong. Apologies for my ignorance!
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Old 09-05-2010, 06:49 PM   #6
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Default Re: how to test spark?

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Nick,

The T and the A use different ways to generate the ignition voltage.

The model T uses a coil/interupter that generates high voltage when it gets 6 volts. The timer switches 6 volts to the different "buzzboxes" for each cylinder.

The Model A uses a set of points that open and close instead of the vibrating interupter. The distributor then switches the high voltage to the different cylinders. The Model A has one coil for all cylinders. The model T has a coil for each cylinder.

Two very different methods...in essence a low voltage switching vs a high voltage switching.

By the way, Atwater Kent invented the points/coil system. Later, he went on to start a radio company.

Marc
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Old 09-05-2010, 06:53 PM   #7
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Default Re: how to test spark?

ah. okay i just figured they would be somehow related.

thanks for the history though!
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Old 09-05-2010, 06:53 PM   #8
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Default Re: how to test spark?

Nick, it is possible to use a jumper wire to bypass your missing igniton switch. If you successfully bypassed the switch, you should be able to use those same testing procedures. It might help you to look at the link at the MAFCA site. It also has the complete wiring diagram description of the ignition circuit. Why do you think that your pop out switch is bad?
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Old 09-05-2010, 06:55 PM   #9
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Default Re: how to test spark?

I thought Kettering of GM invented the points & coil ignition? http://en.wikipedia.org/wiki/Ignition_system

There is also this reference about Atwater Kent http://en.wikipedia.org/wiki/Ignition_coil
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Old 09-05-2010, 07:04 PM   #10
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Default Re: how to test spark?

Bruce,

My earlier comment was somewhat...broad. Kettering came up with the original point/coil concept and Kent came up with the improved, coil we have today.

Thanks for the comment.

Marc
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Old 09-05-2010, 07:07 PM   #11
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Default Re: how to test spark?

Quote:
Originally Posted by MCHinson View Post
Nick, it is possible to use a jumper wire to bypass your missing igniton switch. If you successfully bypassed the switch, you should be able to use those same testing procedures. It might help you to look at the link at the MAFCA site. It also has the complete wiring diagram description of the ignition circuit. Why do you think that your pop out switch is bad?
not so much bad, as my 6 keys i found in the car don't work with the ignition, but work with the doors haha
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Old 09-05-2010, 07:42 PM   #12
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Default Re: how to test spark?

If it is an original, you should be able to get a key for it. In fact, any competent locksmith should be able to make you a key for either an original or reproduction pop out switch.
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Old 09-05-2010, 08:56 PM   #13
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Default Re: how to test spark?

Not sure what you mean that "nothing happens" when you move the spark lever. The plate in the distributor should move. Maybe I am taking you to literally here and dont mean to be a wise....
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Old 09-05-2010, 09:08 PM   #14
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Default Re: how to test spark?

i mean't like, the engine doesn't respond to the spark being advanced or retarded while i'm turning it over.
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Old 09-05-2010, 10:34 PM   #15
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Default Re: how to test spark?

I'm out in Brentwood, east of san francisco. Give me a call. I might be able to help you out. (925)872-3639. Bob
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Old 09-05-2010, 11:08 PM   #16
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Default Re: how to test spark?

Quote:
Originally Posted by MCHinson View Post
If points are sparking then disconnect the coil center (high tension wire) from the distributor cap (leave connected at distributor end). Place the free end of the coil wire about 1/8" from one of the engine head nuts.
Should read; ...disconnect the coil center (high tension wire) from the distributor cap (leave connected at Coil end).
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Old 09-05-2010, 11:51 PM   #17
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Default Re: how to test spark?

Not sure how you bypassed the ignition switch, but if it's an original popout switch it grounds the points in the off position, so to bypass it you would have to have the end unscrewed from the distributor. In an emergency I have used a cork and nail to make contact from the points side of the coil to the contact bar inside the distributor base.
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Old 09-06-2010, 12:01 AM   #18
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Default Re: how to test spark?

if i'm not mistaken, the ignition switch closes and opens the electrical circuit required for the engine to run(well that's how it is looking). So like when you hotwire a more modern car, we took the two wired from the back and attached them together to open the loop permanently.

I'll try some of your suggestions when I have a chance off from football/school. Unfortunately I normally only have Sundays and evenings off so I may not be able to ring you up soon(Bob). I do appreciate all the help, and not getting fed up with this youngin!
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Old 09-06-2010, 12:18 AM   #19
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Old 09-06-2010, 07:16 AM   #20
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Default Re: how to test spark?

Quote:
Originally Posted by firefirefire90 View Post
if i'm not mistaken, the ignition switch closes and opens the electrical circuit required for the engine to run(well that's how it is looking). So like when you hotwire a more modern car, we took the two wired from the back and attached them together to open the loop permanently.

I'll try some of your suggestions when I have a chance off from football/school. Unfortunately I normally only have Sundays and evenings off so I may not be able to ring you up soon(Bob). I do appreciate all the help, and not getting fed up with this youngin!
I guess you mean "close the loop" when you tie the wires together, rather than "open the loop".

Notice in the schematic that Mike posted the switch is shown in the OFF position and the points are GROUNDED. When the key is turned to the right and it pops out, the points wire will be connected to the coil primary wire and DISCONNECTED from ground. The grounding of the points wire is why the end of the popout cable must be unscrewed from the distributor if you are going to hotwire the original ignition. If you are using an ordinary aftermarket switch, then hotwiring as you describe should work fine.
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