My Tractor Forum banner
1 - 20 of 23 Posts

·
Registered
Joined
·
12 Posts
Discussion Starter · #1 ·
Hey all - I’ve an early-80’s 318 repowered with a newer P218.
Tractor had no spark when I bought it.
  • Had 12 volts coming to the three pin connector
  • I noted that the wire going to the coil had 12 volts when unhooked, but when hooked up - it only read at 2 volts (Capacitor??)
  • No Spark when jumping the + terminal on the coil
  • Coil had 3.8 ohms on primary towers, and only 17K ohms on the secondary. Out of spec, so I replaced.
  • Put a new coil in and it fired right up! Until today…
  • Started diagnosing the coil again, and when I jumped the NEW coil to the + terminal - it sparked. Weirdly enough, I hooked the plugs back up and the engine ran.
  • Engine sat idling for maybe 2 minutes and then died flat. NO SPARK.
-Checked resistance on NEW coil. 3.8K on primary, and only 21K on secondary. Did I somehow just fry my new coil??

Two things potentially: Is the condenser going and robbing power to the coil somehow? It’s still only reading 2V between coil + tower and battery ground.
Second: Could a bad ignition control module somehow be frying my coils?? I hooked my multimeter between the - coil post and battery ground, rotated the flywheel, and it read between 1.9 - 1.95 volts. Not in spec, unless the coil has to be working properly in order for the ICM to read correct. Please help before I start loading the parts cannon!
Wheel Tire Vehicle Motor vehicle Tractor



-
 

·
Kish JD 318/420/430
Joined
·
4,781 Posts
Where is the condensor hookup to on the coil? As a check disconnect the condensor and see if it starts. If it does the condensor is failing (leakage - allowing current to pass to ground. Check seat safety switch (must have more than 50 pounds to close the switch in the seat) and the ground speed safety switch (in neutral position) and brake safety switch if a post 1990 year build date. It could also be a bad electronic ignition module (located behind the flywheel).
 

·
Registered
Joined
·
12 Posts
Discussion Starter · #3 ·
Thanks for your quick insight - the white powered wire, red ICM wire, and black condenser wire are hooked up to the (+) post on the coil. Only the Black ICM wire is hooked up to the (-) post on the coil.

I removed the condenser wire from the post and was still reading only 2-2.5 volts On the (+) terminal.
I tried pulling the red ICM wire from the positive post and to my surprise, I then had 12v at the (+) terminal.

I pulled all the wires off and pressed the white 12v supply directly to the red ICM wire and achieved the same results - it immediately pulled the reading down to 2 volts.

So, I’m assuming the ICM is to blame. However - would the ICM somehow fry my coil also? The resistance of a coil that was new less than an hour ago is now out of spec.
Thanks!


Motor vehicle Electrical wiring Gas Automotive exterior Cable
 

·
Registered
Joined
·
12 Posts
Discussion Starter · #5 ·
Based on the manual your secondary windings are not in spec. Ohms should be 34.02 - 41.6 K-ohms at 68 degrees.
Agreed! I'm trying to decipher whether an issue with my ICM could have fried a new coil, or whether my new coil just went bad within an hour.
At no point have i been able to read 12v to the positive terminal of the coil while the ICM wire was there also. Even when the tractor was running.
Thanks!
 

·
Kish JD 318/420/430
Joined
·
4,781 Posts
Coil readings depend on if it's the old original or a replacement coil. I have a old replacement style coil here the primary side reads 3.2 ohms (weird to be that low, but maybe OK) and the secondary reads 21 K ohms. But it all matches with what you posted in #1
Always measure coils with nothing else attached, the other stuff can give wrong readings.
 

·
Three of my friends
Joined
·
9,653 Posts
check the ground under the battery.
 

·
Three of my friends
Joined
·
9,653 Posts
Delete
 

·
Registered
Joined
·
12 Posts
Discussion Starter · #10 ·
Coil readings depend on if it's the old original or a replacement coil. I have a old replacement style coil here the primary side reads 3.2 ohms (weird to be that low, but maybe OK) and the secondary reads 21 K ohms. But it all matches with what you posted in #1
Always measure coils with nothing else attached, the other stuff can give wrong readings.
Brilliant. You’ve just reminded me that my coil is, in fact, within spec :ROFLMAO:
Going to check the condenser shortly.

Also worth noting that i had the back of the dash tower off and was pulling on the dash / wires trying to get the control lever out. That wouldn’t explain the sudden stop while running though.
 

·
Registered
Joined
·
12 Posts
Discussion Starter · #11 ·
Went out to the garage - gave the tractor a cursory crane and IMMEDIATELY had spark, for no apparent reason. Weak, but there. Took the condenser off and bench tested - had my multimeter needle jumping in both directions as it should.
I installed the replacement condenser that came with my coil since I had it.
Turned it over, and seemed to be getting a much stronger spark.
I was also getting 12V to the coil, which is the real mystery to me as I yesterday the red ICM wire was robbing voltage not the condenser wire

It runs beautifully for now, but I still have a hunch it’s going to act up again and point towards The ICM being the ghost behind the curtain - thanks all for now!
 

·
Kish JD 318/420/430
Joined
·
4,781 Posts
I think that you disturb some wiring going to the TDCM, the plug connections are known to get corrosion after such a long time. I think you will need to clean the connection in the plugs sooner or later.
 

·
Premium Member
Joined
·
7,676 Posts
My 420 had a main breaker that the studs where so corroded it would die after 30 minutes. Used a test light to see where I was loosing power


Sent from my iPhone using Tapatalk Pro
 

·
Registered
Joined
·
12 Posts
Discussion Starter · #14 ·
Update: replaced the ICM + spark ring last night (it tested bad - was fluctuating between 1.5 and 0 volts) - still no spark, and voltage to the "+" coil is still dropping to 2 volts when i hook up the white ICM wire.
I jumped the "+" coil to battery "+" last night and briefly had spark and 12 volts at the coil. I haven't been able to replicate this scenario - still only 2 volts at coil and no spark as of this morning, even when jumping. Will be tooking at the TDCM connections next..
 

·
Three of my friends
Joined
·
9,653 Posts
Have you checked the ground wires under the battery,there’s 3 wires that go into on for a ground
 

·
Registered
JD317, JD318, JD430GT
Joined
·
810 Posts
Here is a test to try...

Disconnect the 12V supply wire from the coil (I believe that is the white wire). Check voltage (guessing it might be 12V). Connect that wire to a light bulb (like your headlights) and check the voltage. It should remain at 12V. If it does not stay at 12V, it tells me that you have a bad connection somewhere. When no current is being pulled, you get 12V. As soon as current flows, the bad connection robs the voltage.
 

·
Registered
Joined
·
12 Posts
Discussion Starter · #17 ·
All - I pulled the battery out - cleaned all the TCDM connections, cleaned the ground wire connection, and still no spark.
I'm at a complete loss at this point. The biggest question mark is why my ICM is robbing voltage to the coil when it's connected. I just tested resistance across the circuit breaker posts - .3 OHMS - spec says no resistance - is that enough to be out of spec?
 

·
Registered
Joined
·
702 Posts
Looks like you might have posted around the same time as CantKeepUp, so i'm not sure if you saw that post or not, but it contains valuable info..

Voltage drops when current flows across resistance. When you hook up the ICM it is not 'robbing' voltage. The voltage is being consumed upstream of that, by a high resistance in the wiring. Since nothing is apparently overheating to any dangerous smelly smoky extent, it is probably safe to plug the ICM in, let the voltage at the ICM drop to 2, and then look for the voltage drop upstream either by feeling around for heat buildup (the bad connection will get warm, but if it's inside a large component like ignition switch it may not be externally detectable by hand), or by checking voltage from point to point until you find an area where it drops roughly from 12 to 2, and then zero in on it.

However, that's not to say the ICM itself isn't bad. Voltage drop across a given resistance rises proportionally to current flow. If voltage doesnt change, the way to increase current flow is to lower resistance. If the ICM has lower resistance in that circuit than it should (like if that part of it was shorted to ground), it would increase the total current flow AND shift where the voltage is being dropped, from primarily inside/after the ICM (when that part of the circuit held most of the resistance), to primarily outside/before the ICM (outside/before now represents a greater proportion of total circuit resistance because the ICM presents less).

So you still might have a shorted ICM. But you shouldn't be able to drop 10v in the wiring anyway. Any current level that would make an otherwise good connection drop 10v should be instantly popping fuses. If you are flowing current below fuse rating AND dropping 10v in the wiring, the wiring is bad and should be diagnosed regardless of the ICM being good or bad.
 

·
Registered
JD317, JD318, JD430GT
Joined
·
810 Posts
You can think of voltage as water pressure and current as water flow in your garden hose. If you turn the water spicket nearly off, you will just get drips and no real pressure out of the hose end. If you close off the end of your hose and let it closed overnight, the "drips" will eventually fill the hose to the same pressure in your house. However, if you open the end of the hose, you will get a very short spurt of high pressure water flow, but then it will quickly be back to drips and low pressure.

If you have a bad connection somewhere in the wiring, it is like the closed spicket. It resists almost all flow (it is high resistance). If nothing is connected to the end of the wire (no place for current to flow), then the voltage (pressure) will rise up to 12V. As soon as you give it someplace to flow, you go back to low current and low voltage.

This does not mean that you will have high current somewhere else that will or should blow a fuse or melt a wire. That happens when you have a low resistance connection to ground.

So I suspect you have a bad connection.

One thing that might say otherwise....I think you said that you took 12V battery to the coil and had 12V. But now if you do the same thing, are you saying that you are back to 2V? Going straight from the battery should bypass any bad connection.
 

·
Three of my friends
Joined
·
9,653 Posts
I wonder if you have a bad safety switch,just bad enough to let a small amount of power through
 
1 - 20 of 23 Posts
Top