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Discussion Starter #1 (Edited)
Hello everyone. I have a late 80's John Deere 322 that I have had for about 12 years now or so. Tractor always ran like a top until 2 weeks ago. While I was using it, it suddenly started to miss. I drove it back to my barn and looked at it later once it cooled off. In looking at it, I discovered the middle ignition coil was cracked and actually started to melt. Okay, that would explain it, so I ordered a new one from John Deere and replaced it. Started it up and it still had a miss. I've used a spark tester, between the boot and the plug, but no spark. In further checking, I am also seeing that I am not getting any spark from the ignition coil to the right hand side as looking at the tractor from the front end.

I've checked the voltage at each of the 3 ignition coils and am seeing about 11-12 volts on each, at the orange wire.
I'm started it up, running on 1 cylinder and used a test light going from the engine ground to the negative post on the ignition coil. (flickers on the left hand ignition coil as that cylinder is working, stays on constant for the middle one and a very weak glow from the ignition coil on the right)
I know the ignition coil that I put in is good since I pulled the wires off of the one with the plug which was firing and swapped the plug wire as well, and it works.

So I know I have at least 2 good ignition coils, but am not sure why the middle one doesn't send any spark. As I mentioned, while it is running, with the test light on the negative lead of the coil, the light just stays on and doesn't flicker. I did also check the resistance between the positive lead from the ignition coil to the plug boot end and it's in the ballbark of what is listed in the manual, which in my case was around 12-14K-ohms.

The other ignition coil appears to be bad as the resistance as mentioned in the 7k - Ingnition Coil Tests - Secondary Windings, there isn't any Nothing is showing up on my meter for that one at all. So I assume it's bad and that is the one in which the test light shows a very faint glow, on the negative wire on the coil when it's running.

I'm open to any idea's or thoughts. I do have the service manual. And while I'm certainly not an expert mechanic or anything, I would like to think I can figure this out with some assistance.
 

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John,

:welcome:

Your issue is not the coils but the transistor module or the pulsars (or perhaps the wiring in that area.)Since you have the TM1591 service manual, I will reference that document. Here is an excerpt of the wiring in that area and a simple test you can do with an ohm meter on the transistor module.

322 ignition wiring diagram.JPG 322 transistor module resistance tests.jpg

The red circle in the wiring diagram highlights a connection to another part of the circuitry that enables the ignition under certain conditions when the operator is not on the seat...but since you have voltage at the + sides of the coils that is not your issue here. Below is a larger file with some theories of operation from that same TM1591 manual...please let us know what you find when you test the transistor module. A failed transistor module that keeps the coil primary on at all times could burn out the coil as you experienced.

View attachment 322, 330, 332 and 430 electrical fromTm1591.pdf


Chuck
 

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Discussion Starter #3
I do have that particular manual, but I do appreciate you pointing this out. As it would make sense, as to why that one ignition coil burned up and started to melt. I will check these connections, as it looks like I might have an easier time from underneath with the deck removed. I also looked up a price on that Transistor module as well, and boy, that thing is not cheap at all.
 

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Discussion Starter #4
Okay, I pulled the transistor module out and have it sitting on my desk, so that I can test the resistance easier. And in looking at the chart, some of the values I am getting are much higher than mentioned in the document. I do see the note which mentioned that what's most important is either there is continuity or there isn't. For example:

Black - Brown 2.0
Black - Green/White 2.0
Black - Green 1.99


Black - Black/Yellow 57.4 and keeps climbing
Black - White 2.34
Black - White/Blue .37
Black - Orange/White .336
Black - Black/White .4




Brown - Black 2.04
Brown - Green/White 4.08
Brown - Green 4.05


Brown - Black/Yellow 65 and climbing
Brown - White 4.38
Brown - White/Blue 170 and climbing
Brown - Orange/White .380
Brown - Black/White 2.04
 

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Discussion Starter #5
I also checked the resistance fir the Pulsar Coils and it looks like one might be bad as well.

The resistance came in at:

No 1 - Grn/Wht 21.3
No 2 - Brn 21.3
No 3 - Grn 6.93

JD_Pulsar_coil_test.jpg
 

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John,

From your post #4 above it looks like you may have an auto-ranging meter...the range information and lead polarity used is not clear from the numbers quoted. I could make a reasonable guess that line 1 (black wire to brown wire) is the first cell of the table where the black wire is connected the red lead of your meter and the brown wire is going to black lead of the meter, where the expected resistance would be 2.2k (2,200 ohms) and you found 2.0 (presumably k-ohms..)

Note that the table should yield quite a few more readings than you list, since each combination of color pairs is measured in both forward and reversed polarity. to fully complete the matrix, you need to make 90 individual measurements. Please let us know what you actually find at each table intersection -- maybe copy the chart and add your readings in another color.

The one pulsar measurement is of concern as you noted. But if you find that the transistor module is indeed bad when you have it fully characterized with your meter measurements, I would suggest changing the TM out prior to committing to replacing the pulsar in question.

Chuck
 

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Discussion Starter #7
Marking the values on the chart was an awesome idea. Much easier. Here are the complete findings. Anything with just a zero, was no reading at all or no change. A number of the readings jumped from the k-ohms to M-ohms and are identified as such.

John_Deere_Transistor_Module.jpg
 

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Discussion Starter #8
Update - I just installed the new transistor module and it's running like a champ. Expensive little part too, but I was able to find it for 275.00 from a John Deere dealer online. Thanks for the help with this as I appreciate it a lot.
 

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Glad you got it sorted out!! To paraphrase Sherlock Holmes -- once you eliminate the easy and less expensive causes, the remaining one (no matter how costly) is worth considering as the real culprit...

Chuck
 

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Thanks, Keith, for moving this to the Tech FAQ section.
 
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