John Deere MT no spark.

Hey there ! I?m new to this website and new to owning a tractor. I got the tractor given to me from my mother in law. It does run but I am running into some issues and it won?t start Now. I have a John Deere MT. I have spark from the coil wire when I put it against the metal of the tractor. I did put a new cap, rotor , condenser, points , plugs and wires on it. Also a new coil. I got it to run but it seemed rough and backfiring a little through the muffler. After I shut if off. I tried to start it the next day and it just won?t start. I set all my gaps to what the manual says. Basically I have no spark to the spark plugs. But has spark at the points. This might be a silly question but , if I take my test light and put it in the coil where the wire goes should it light up ? If so , then mine doesn?t. But when I put the wire in and hold it up to the block it has spark. Any advice is much appreciated.
 
Swinney, good questions, you ask


1) "This might be a silly question but , if I take my test light and put it in the coil where the wire goes should it light up ?

Problem with that test is if you have a typical what I suspect low voltage 6/12 test light, the coils top HV output tower is several thousand volts (when good points conduct coil current then open) and may well NOT yield any visible short term HV light output like 12 steady DC volts would produce and may damage the test light !!!!!!!!!!!


2) But when I put the wire in and hold it up to the block it has spark.

That's what I would expect if all is working, you're looking for a good visible bright blue spark to frame at approx. 3/16 inch NOT any faint thin wimpy hard to see yellow spark

If you have a good bright blue spark out the coils top HV tower (via a wire to frame ground gap) when the coil fires but NOT any spark out of any of the plug wires to ground or across a good correct connected plug gap, THE PROBLEM MUST BE THE COIL WIRE,,,,,,,,, OR THE DIST CAP,,,,,,OR ROTOR,,,,,,,,,,OR THE WRONG CAP OR WRONG TIMING whereby the rotor tip isnt lined up with an internal cap pickup when the points break open.

I have seen INCORRECT DISTRIBUTOR CAPS cause that or they weren't installed correct either of which isn't allowing the rotor tip to be in line with a caps internal pickup when the points open and the coil fires

With the cap off and ign off slowly turn the engine over until the points just break open ands stop,,,,,,,look at the cap and where it would be if installed and see if the rotor tip is lined up with where one of the caps pickups are located,,,,,,,,when the points break open the rotor tip should be close to one of the caps internal pickups...IF ITS THE RIGHT CAP AND INSTALLED CORRECTLY

If you have no fire at all you can work through my Ignition Troubleshooting Procedure linked below BUT if you get a good bright spark out the coils top HV tower the points etc is working but no fire out any of the caps terminals I suspect the cap or rotor or wires or wrong cap or a distributor or timing problem.........

NOTE ALSO when you say it runs rough ARE THE PLUGS AND WIRES IN THE CORRECT FIRING ORDER SEQUENCE ????????? If not she may run bad or not at all depending on how many if any wires are correct BUT THAT WOULDNT CAUSE NO FIRE OUT THE COIL AT ALL IF ALL ELSE WAS OKAY

I take it the distributor is installed correctly ??????????

For this discussion I'm assuming you have the correct voltage coil (for example not a 12 volt coil on a 6 volt tractor etc) and the points and condensor are all okay ARE THEY ???????????? I AM ASSUMING you get a good spark out the coils top HV tower but no fire to any of the plug wires or plugs IF THATS INCORRECT LET ME KNOW AND I WILL PROVIDE A DIFFERENT RESPONSE !!!

Wrong cap or not installed right,,,,,,,,,,rotor or cap problem,,,,,,,,,,,incorrect plug wire on cap firing order,,,,,,,,,,timing or distributor problem,,,,,,,,,, ???????????????


Let me know, post back your findings and any questions


John T Retired Electrical Engineer
John Ts Ignition Troubleshooting Procedure
 
"[b:654c4848f0][i:654c4848f0]<font color="#6699ff">if I take my test light and put it in the coil where the wire goes should it light up ?[/i:654c4848f0][/b:654c4848f0]</font>"

No.

Take a look at these videos that demonstrates/discusses the spark from the secondary winding in the coil.

<a href="https://www.youtube.com/watch?v=W94iksaQwUo">How Ignition System Works</a>

<a href="https://www.youtube.com/watch?v=5kvj_d72WTo">This is how you can test a ignition coil</a>

?[b:654c4848f0][i:654c4848f0]<font color="#6699ff">I have spark from the coil wire when I put it against the metal of the tractor.[/i:654c4848f0][/b:654c4848f0]</font>?

You might consider using an in-line ignition spark tester.

a178470.jpg" width="650"


a178471.jpg" width="650"


[b:654c4848f0][i:654c4848f0]NOTE: Please be mindful of common safety steps; expressed or not[/i:654c4848f0][/b:654c4848f0].

Using the in-line spark plug tester, attach the open end to the spark plug.

Attach the probe end to the spark plug wire.

a178472.jpg" width="650"


Turn the ignition switch [b:654c4848f0]ON[/b:654c4848f0] and engage the starting motor.

If the in-line ignition spark tester light flashes, then the spark plug wire is good; otherwise check the spark plug.

If the in-line ignition spark tester light does not flash, then check the spark plug wire.

Using the in-line spark plug tester, attach the open end to the distributor cap.

Attach the probe end into the spark plug wire.

a178473.jpg" width="650"


Turn the ignition switch ON and engage the starting motor.

If the in-line ignition spark tester light flashes, then the distributor cap is good; otherwise check the spark plug wire.

If the in-line ignition spark tester light does not flash, then check the rotor.

Make sure the tip of the rotor is making good contact with the top terminal inside the distributor cap.

a178475.jpg" width="650"


Hope this helps.
 
NICE pics James, as they say, A PICTURE IS WORTH A THOUSAND WORDS those in line HV spark testers are a good thing, I usually just used a good grounded spark plug to get you by in a pinch lol

John T
 
Had a Model 70 that sat for a year and would not start.

Put in a new pair of spark plugs, but still no start.

Checked all that could be tested with the light tester.

Had power to the points.

Connected the in-line ignition tester between spark plug and spark plug wire.

Tractor started and the light started flashing.

Enjoyed the small light show for a while and tried to photograph the light, but no success.
a178506.jpg" width="650"
 
I hear that James, perhaps a video may have captured the flashes ??? Regardless, those inline HV testers are a handy tool. Again great to see the pics you so often post... As I recall a few of the WRONG Two Cylinder Distributor Caps can still fit (or maybe 180 out???) BUT the internal pickups aren't in the correct location !!!!!!!!! That (if true, no warranty lol) could account for a good coil spark but none out the plug wires, Oh well, we may get him started in the right direction.

John T
 
Getting a new cap tomorrow and also installing a new switch and complete harness. The wires were bare inside Of the dash of the tractor. It was a mess. Plus all new gauges. The cap looked identical to the old one. But I will see if that makes a difference. Fingers crossed. I appreciate all the help and pictures from you guys. It makes this experience for me a lot better.
 
Ok so I got the harness and gauges installed. As well as a new switch. I got the tractor to start and run. But it?s smoking pretty bad which it didn?t before. And it?s running really rough. I didn?t see any marks that say ? spark? or ?tdc? on fly wheel. Idk where to start. But needless to say I got spark and it?s running now.
 

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