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Testing spark to spark plug
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pernest
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PostPosted: Fri Nov 25, 2022 9:10 am    Post subject: Testing spark to spark plug Reply with quote

I understand that you can test a coil by pulling the wire to the Dist and holding it near a ground for spark but can you test each spark wire by moving the Dist rotor past each rotor contact (fully assembled dist) via cranking the generator pulley to check for spark in the same manner?

Sorry for the awkward description above. I just want to rule out ignition problems before going to fuel issues.
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67rustavenger Premium Member
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PostPosted: Fri Nov 25, 2022 9:54 am    Post subject: Re: Testing spark to spark plug Reply with quote

You can.
But a word of caution.
If your engine easily starts. Turning the gen pulley to test for spark while the ignition is in the run position. There is a chance the engine can start.
That would be a very bad situation. Be careful.

You can pull a sparkplug lead from the distributor while the engine is running. To see which cylinder is not firing.
Pull the wire and if there is no change in RPM/running. You have found the dead cylinder.

I use one of these tools to test spark, on individual sparkplugs.
https://www.amazon.com/Deal%E3%80%91OriGlam-Adjust...amp;sr=8-7
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pernest
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PostPosted: Fri Nov 25, 2022 11:39 am    Post subject: Re: Testing spark to spark plug Reply with quote

Thanks for the word of caution.

The engine was running fine up to when I discovered a problem which required shroud removal.

After reinstalling the shroud, I could not get the engine to operate -- it cranked but would not fire. I realized that I might have misdirected the spark wires so I corrected that with many rechecks. Eventually got the engine to run but only very poorly. No idle.

Want to explore all ignition problems before going to fuel matters. No. 1 is at 2:00 on my distributor and I have accounted for this in routing the wires.

Your caution about danger will be well heeded. Thanks again!
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67rustavenger Premium Member
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PostPosted: Fri Nov 25, 2022 12:41 pm    Post subject: Re: Testing spark to spark plug Reply with quote

With the engine at TDC remove the dist cap and not the position of the rotor.
If you indeed have it at TDC. That will be your #1 lead position. follow the #1 lead from the plug to the cap. Make sure that you're dead sure it's correct.
Move onto the next three in order 4, 3, 2.

Usually what I get backwards is, the position of the three and four leads. Embarassed
The engine will run that way. Just poorly!
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Cusser
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PostPosted: Fri Nov 25, 2022 1:04 pm    Post subject: Re: Testing spark to spark plug Reply with quote

I like a spark test tool like below. I just used mine to diagnose a no-spark condition on my 1988 Mazda truck.

https://www.harborfreight.com/search?q=spark%20test
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ashman40
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PostPosted: Fri Nov 25, 2022 1:24 pm    Post subject: Re: Testing spark to spark plug Reply with quote

I recommend taking 67rustavenger's steps 1-step further to confirm your have the plug wires in the correct position...
    Start by removing all the plug wires from the distributor cap.
    Remove the wires from the spark plugs.
    Pull all wires out from the engine and using a permanent marker or paint pen, mark both ends of each plug wire with the cylinder# for that wire. The long wires will be #1 and #2. The short wires will be #3 and #4. By marking both ends with the same# you can tell from the distributor end of the wire exactly which wire you are working with. I cannot tell you how many times I mixed up the #1 and #2 wires as they pass under the generator stand.
    Re-run the spark plug wires to their respective cylinders. Leave the cap end disconnected for now.
    Remove the spark plugs from the head and install them into the end of the plug wires. Leave the plugs out for now as we will test them outside the heads.
    Rotate your crank pulley until the TDC mark lines up with the case split. At this point either #1 or #3 piston is at TDC. From the crank pulley alone you cannot tell which.
    Remove your #1/#2 valve cover on the right side of the engine.
    While you look at the #1 rocker arms (right front most rocker arms), rock the crank pulley back and forth around the TDC mark. The #1 rocker arms should NOT move. Push and pull on the #1 intake and exhaust rocker arms and there should be the slightest of play. 0.006" if they are gapped correctly. This confirms the #1 valves are closed.
    If you find the #1 rocker arms are moving when you rock the crank pulley back and forth... you are at #3 TDC, not #1. Rotate the crank pulley 360deg until the TDC mark is once again lined up with the case split. Retest and now #1 rockers should not move when the crank pulley is rocked. You are now at #1 TDC.
    Look at the distributor rotor and where the tip is pointing. This position around the cap is where the #1 spark plug wire is placed. You know this because the #1 piston is at the end of its compression stroke (valves closed and piston at TDC) and it is expecting a spark to be delivered by the distributor to the #1 spark plug. This is done by placing the #1 plug wire into the distributor cap post over the tip of the rotor.
    Install the distributor cap. It is notched and can only be installed 1 way.
    Install the "#1" plug wire into the post over the rotor tip. You are ensuring the distributor delivers the spark to the #1 cylinder.
    Install the remaining plug wires in the CW order 1-4-3-2 using the numbering on the end of the plug wires.

You are done. All plug wires are in their correct position around the distributor. We did this without any assumptions. We confirmed the engine was in a position ready for the spark to be delivered to cylinder #1 and then arranged the distributor so it delivered the spark to the correct wire/spark plug.
You can now set your point gap/dwell and then static time your distributor to 7BTDC at this point just to get it started.


Testing spark to the spark plugs... (the following works for points but might damage electronic points/ignition modules. Use at your own risk!)
    Remove the small gauge green or black points wire running from the distributor to the ignition coil #1 (-) terminal.
    Test that there is 12v at the ignition coil #15 (+) terminal when the key is in the ON/RUN position.
    Remove the distributor cap and rotate the crank pulley CW until the point contacts are open.
    Rotate the crank pulley CCW until the point contacts just close.
    Install the distributor cap noting which post and spark plug wire# the rotor is directly under.
    Using your battery jumper cables, connect one end of the black cable to a good ground point. With the other end of the black cable clamp it to the body of the spark plug connected to the cylinder head end of the plug wire the rotor is under. The jumper cables will ground the spark plug.
    With the ignition ON and providing 12v to the ignition coil, touch the green wire to the #1 terminal of the coil. Hold it there for a couple seconds and then remove it from the #1 terminal. Upon removing the wire you should see a spark jump between the spark plug electrodes. Do this a few times to test. The spark should be blue-white in color.
    Rotate the crank pulley 180deg CW. If necessary, confirm the points are once again closed.
    Repeat the test with the next plug wire# 90deg CW on the distributor cap. Clamping the jumper cable to that # spark plug.
    Repeat for all 4 spark plugs.

This test confirms the coil is able to send a spark to each spark plug. If the spark quality is different for one spark plug test the resistance over the spark plug wire and thru the center electrode of the spark plug. Resistor spark plugs and wires will have higher than zero resistance thru the conductors to reduce radio noise. Longer plug wires will have higher resistance, but similar length wires should have about the same resistance so compare the resistance between the wires of same length.
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pernest
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PostPosted: Fri Nov 25, 2022 5:31 pm    Post subject: Re: Testing spark to spark plug Reply with quote

Having recently adjusted the valves and noting the number 1 cylinder at the 2:00 position, Iím certain that Iíve got the spark wires correct in 1-4-3-2 sequence. Will check strength of spark to each cylinder.

Itís possible that the poorly running engine is fuel related. Will let yíall know what I eventually find. Thanks for the great feedback!
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pernest
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PostPosted: Fri Nov 25, 2022 7:28 pm    Post subject: Re: Testing spark to spark plug Reply with quote

Having recently adjusted the valves and noting the number 1 cylinder at the 2:00 position, Iím certain that Iíve got the spark wires correct in 1-4-3-2 sequence. Will check strength of spark to each cylinder.

Itís possible that the poorly running engine is fuel related. Will let yíall know what I eventually find. Thanks for the great feedback!
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PostPosted: Sun Nov 27, 2022 7:23 am    Post subject: Re: Testing spark to spark plug Reply with quote

this is all you need to test for spark, bend the tabs to adjust. One wire goes to the ignition wire then ground the other wire end to 'metal' that way no chance of accidental engine start while testing.

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pernest
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PostPosted: Sun Nov 27, 2022 10:27 am    Post subject: Re: Testing spark to spark plug Reply with quote

Iím now ďpretty certainĒ that Iím wired correct as far as Dist to cylinders. Used a In-Line spark checker, cranked the rotor just before each firing position in the Dist, closed the cap and cranked the rotor just past each firing position to see if the light flashed. The test showed that the spark wires all matched up. Did a compression check and all cylinders were 100 # or just over. Still canít get the beast to start quickly and run well. Will advise.
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pernest
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PostPosted: Mon Dec 05, 2022 6:35 pm    Post subject: Re: Testing spark to spark plug Reply with quote

Took care of the issue requiring shroud removal, reinstalled shroud, cleaned carb, cleaned Dist (adjust pts and lightly oiled top plate), did static timing, and found that coil was okay when engine came to energetic life! Wow, installing the shroud/ generator with engine in car ó not easy!
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Cusser
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PostPosted: Mon Dec 05, 2022 6:49 pm    Post subject: Re: Testing spark to spark plug Reply with quote

pernest wrote:
Wow, installing the shroud/ generator with engine in car ó not easy!


I've done it, on both my 1970 and on my 1971 VW Convertible....
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