Weak spark at points

[13fx]

Went to test start an engine today and am getting intermittent spark spark. Wanted to see what was happening so I put the timing light on the coil wire and was seeing spark once every 2-3 rotations of the crank. Pulled the cap off and started checking spark at the points. The spark there is weak. I took the condensor off and the spark got weaker. I have checked resistant on the line coming into the coil and it is fine. I checked the coil and it tested ok. I replaced the coil with one off a running tractor and nothing changed. The battery reads 6.8v the coil on the low side reads 6.4 when open, the high side reads 6.2-6.3 when closed. I tested the points for resistance and they tested fine when closed. Tried a new rotor, I've tested the plug wires for resistance and they test fine. The plugs have all been pulled and cleaned. Resistance from the coil to the points tests good. I'm not very good with electrical work and have run out of ideas.

 

[tomturkey]

If only we had more hands, we could test things while we we pushing on the starter button/switch/key. For me it it has been a bad wire or corroded connection in the ignition circuit that was starved for power when the starter motor was engaged. Your description of your testing procedures have probably already eliminated this possibility, but thought I would mention it. FOR ME, electrical problems make my brain hurt lol gobble

 

[farmersamm]

I had a hard time wrapping my head around how the points collapse a magnetic field in the coil.............which makes it send out a powerful spark. Still don't fully understand it.

I do know, from back when I worked on point type ignitions, that a dwell meter would tell you more than a feeler gauge. I always started with the dwell, and worked out from there. Verify it, then check the other components.

 

[13fx]

I had a hard time wrapping my head around how the points collapse a magnetic field in the coil.............which makes it send out a powerful spark. Still don't fully understand it.

I do know, from back when I worked on point type ignitions, that a dwell meter would tell you more than a feeler gauge. I always started with the dwell, and worked out from there. Verify it, then check the other components.

So I've heard the name dwell meter, but I've never seen one nor would I know what do do with it exactly. Can you explain what it does and how to use it please? Thanks

 

[used red MN]

If only we had more hands, we could test things while we we pushing on the starter button/switch/key.

The is a lot of wisdom there from Tom. Although the tests you have performed have some value testing the ignition circuits to see what their voltages are during the cranking mode tells you much more.

I tested the points for resistance and they tested fine when closed.

If the points are basically new this is probably an acceptable test. If the points have been ran a while I prefer to test their ability to provide a ground to the primary circuit against the load of the coil. When they close it should drop to a .5 volts and .2 or less is better. What is the engine and what is it in? Yes answers about Kettering ignitions (points) should be universal but certain system have nuances that need taken into consideration. It seems engines that are 200CID or less give far less problems for a 6 volt cranking system than bigger engines with longer strokes and increased compression ratios from stock such as a Farmall M with Fire Crater pistons. What is the battery voltage you see when cranking? Checking it both at the battery and at the starter can also provide additional insight into proper amperage transfer.

Pulled the cap off and started checking spark at the points

Checking “spark” at the points is one of the most misconceived diagnosis for points. You are actually checking for an “arc” Should you see an arc there when the points are opened? Sure, but judging the effectiveness of your ignition to provide a good spark by that is a guess at best, in fact points that are working the most effectively will show a lesser “arc.” Seeing any kind of spark there only somewhat reliably tells you the primary circuit is seeing some voltage.

Wanted to see what was happening so I put the timing light on the coil wire and was seeing spark once every 2-3 rotations of the crank.

Your timing light is likely powered by the battery, is it a 6/12 volt unit? Operating on 6 volt probably is on the low end of its circuits range to function properly. Back to what is the battery voltage dropping to while cranking? If it drops quite a bit expecting the timing lights induction clamp to pickup every spark is asking a lot. An adjustable gap spark tester is the best tool for checking spark, see link. Example Adjustable spark tester Powering the timing light from a separate battery would help it to be more reliable in this case.

 

[560Dennis]

Are they actually opening at .016 gap with flat point contacts . Or the shaft has to much wear It won’t open contact.Do you have a point file to clean point's contacts ? Clean distribution brass or alunmin coonductive post .
we had off brand condenser that are to small diameter and will not ground at the thighen strap .
randon firing doesn’t make to much sense to troubleshoot there Does it.

 

[Geo-TH,In]

What you can't easily measure is the cranking voltage.
You can't measure the spark plug wire insulation breaking down and the rotor and distributor insulation breaking down under high voltage.
I suggest replacing the rotor and cap .
measuring cranking voltage and running voltage.
If that doesn't work, replace spark plug wires.
You might be making a good spark that is not getting to the plugs.

Edited:
Another test is to measure the coil current. Most are close to 4 amps.

Isn't the job of a good condenser is to minimize the spark when the points open?

 

[560Dennis]

Geo said , was good points also to consider
is the battery cables rated for 6 volt . 12 volt cables to small
battery grounded , test grounds
battery good enough with starter turn ing , load test (at auto parts suggest )
pull trigger on starter ,measure how many volts you got at coil then ?

 

[Brownie450]

You said you tested the plug wires. Are they resistance wires
or solid core? Have you checked the dist. shaft for excessive
lateral [up-down] movement---wear?
If you haven't taken the points out yet, I'd take them out & have
a look at them with a magnifying glass. Check for a nice shiny
surface on both of the contacts. Check for alignment of both
points.
Check for any dirt/ corrosion on any wire in the coil/ dist. primary
circuit. This includes pulling on wires going into a terminal lug.
Jim

 

[Jim.ME]

Went to test start an engine today and am getting intermittent spark spark. Wanted to see what was happening so I put the timing light on the coil wire and was seeing spark once every 2-3 rotations of the crank. Pulled the cap off and started checking spark at the points. The spark there is weak. I took the condensor off and the spark got weaker. I have checked resistant on the line coming into the coil and it is fine. I checked the coil and it tested ok. I replaced the coil with one off a running tractor and nothing changed. The battery reads 6.8v the coil on the low side reads 6.4 when open, the high side reads 6.2-6.3 when closed. I tested the points for resistance and they tested fine when closed. Tried a new rotor, I've tested the plug wires for resistance and they test fine. The plugs have all been pulled and cleaned. Resistance from the coil to the points tests good. I'm not very good with electrical work and have run out of ideas.

How about filling in the blanks? I don't see that you have posted what exactly you are working on for a machine? And front or side mount distributor if applicable.

 

[Ericp351]

So I've heard the name dwell meter, but I've never seen one nor would I know what do do with it exactly. Can you explain what it does and how to use it please? Thanks

Dwell meters. measure duration that points are closed, in deg's. Readings are in inverse of gap.-- that is, big gap= pts open= low dwell, et cetera. Simple, 2 wire hook up, usually coil + a ground. GM cars-points, had a window in cap to adjust Dwell in real time with a hex key. Doing that, each deg of dwell also "fine-tuned" a deg of time. You may also think of Dwell as Duty-Cycle. Good to have a Dwell mtr.,That said, not really needed on conservative tractors if you can handle a feeler + the ALL Important points-file!

 

[PJH]

So I've heard the name dwell meter, but I've never seen one nor would I know what do do with it exactly. Can you explain what it does and how to use it please? Thanks

Dwell meters were especially nice with the old GM distributors that had the little "window" on the side of the distributor cap. You could reach through the window and adjust the point gap (dwell angle) with the engine running. I still have a dwell meter, but it hasn't been used for 35 years. I've never thought of using it on a tractor engine.

 

[PJH]

Dwell meters. measure duration that points are closed, in deg's. Readings are in inverse of gap.-- that is, big gap= pts open= low dwell, et cetera. Simple, 2 wire hook up, usually coil + a ground. GM cars-points, had a window in cap to adjust Dwell in real time with a hex key. Doing that, each deg of dwell also "fine-tuned" a deg of time. You may also think of Dwell as Duty-Cycle. Good to have a Dwell mtr.,That said, not really needed on conservative tractors if you can handle a feeler + the ALL Important points-file!

Sorry Eric for basically duplicating your post. I should have read it through.

 

[wore out]

Went to test start an engine today and am getting intermittent spark spark. Wanted to see what was happening so I put the timing light on the coil wire and was seeing spark once every 2-3 rotations of the crank. Pulled the cap off and started checking spark at the points. The spark there is weak. I took the condensor off and the spark got weaker. I have checked resistant on the line coming into the coil and it is fine. I checked the coil and it tested ok. I replaced the coil with one off a running tractor and nothing changed. The battery reads 6.8v the coil on the low side reads 6.4 when open, the high side reads 6.2-6.3 when closed. I tested the points for resistance and they tested fine when closed. Tried a new rotor, I've tested the plug wires for resistance and they test fine. The plugs have all been pulled and cleaned. Resistance from the coil to the points tests good. I'm not very good with electrical work and have run out of ideas.

Intermittent spark is caused, probably over 95% of the time, by breaker points that don't consistently/reliably make "good" contact each and every time they close.

 

[da.bees]

I'm going off script and say intermittent spark to plugs screams bad condenser. Replace it before you go bald from pulling hair.

 

[TheBartman47]

A good condenser is supposed to reduce excessive arcing on the points contacts. Arcing burns out or builds up carbon deposits on the points and so prevents making good contact thereby not energizing the coil.
A condenser is basically a capacitor, and a coil is an inductor - electrical opposites of each other and so balance each other out. In a capacitor, voltage lags behind current, and in an inductor voltage leads before current.

 

[kencombs]

I may be wrong, again, but I think your points are not making contact. When they are closed the circuit should be grounded and read essentially no voltage from the coil to ground through your meter.Then show battery voltage when they open.

Clean and/or replace them would be my first move. Or, use a test light from the coil to ground and crank the engine it should flash off and on. Failure to do that indicates a poor connection across the points.

 

[13fx]

Went to test start an engine today and am getting intermittent spark spark. Wanted to see what was happening so I put the timing light on the coil wire and was seeing spark once every 2-3 rotations of the crank. Pulled the cap off and started checking spark at the points. The spark there is weak. I took the condensor off and the spark got weaker. I have checked resistant on the line coming into the coil and it is fine. I checked the coil and it tested ok. I replaced the coil with one off a running tractor and nothing changed. The battery reads 6.8v the coil on the low side reads 6.4 when open, the high side reads 6.2-6.3 when closed. I tested the points for resistance and they tested fine when closed. Tried a new rotor, I've tested the plug wires for resistance and they test fine. The plugs have all been pulled and cleaned. Resistance from the coil to the points tests good. I'm not very good with electrical work and have run out of ideas.

So this is a Ford 134 with a side mounted distributor. I have tried a different rotor, a different cap, a different condenser, a different coil and non of that has changed. The points are not new, but I had them put and cleaned them up. The points are not pitted, the contact points on the arm is nice and shiny, the contact points on the base is a dull grey metal that won't shine up. I'm definitely not ruling out the possibility it could be bad points still, but every time I open them manually they throw spark. I have cleaned up almost every metal contract area that I can think of.

 

[Jim.ME]

So this is a Ford 134 with a side mounted distributor. I have tried a different rotor, a different cap, a different condenser, a different coil and non of that has changed. The points are not new, but I had them put and cleaned them up. The points are not pitted, the contact points on the arm is nice and shiny, the contact points on the base is a dull grey metal that won't shine up. I'm definitely not ruling out the possibility it could be bad points still, but every time I open them manually they throw spark. I have cleaned up almost every metal contract area that I can think of.

Do you have a test light? Transmission in neutral. Ground the lead to the block. Put the probe on the coil terminal with the wire that goes to the distributor. Ignition on. Crank the engine over with the starter. Does the test light blink on and off as the engine turns over?

 

[MARK ROBKE]

I was thinking bad distributer cap, after all the parts that were changed, but not the cap (unless I missed that).Mark