# John Deere 316 coil question



## Powermatic66 (7 mo ago)

Hello all, new to your forum. I’m attempting to diagnose an elusive ignition problem on my p218g powered 316. It runs great for 5-10 min, then dies. I’ve replaced the ignition switch, replaced condenser (measured open) , replaced voltage regulator (measured over 17 volts unhooked, but 0 when plugged in correctly. I’ve swapped tdm with another used one from a running tractor.
My question is….can I use an ignition coil from a b43e on my p218g just to see if I’m having breakdown when the coil gets hot? I know they have different parts # due to points/ electronic ignition. I’ve also cleaned all connections and inspected the wiring for shorts/ open connections. Thanks in advance, Jeremy


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## FredM (Nov 18, 2015)

I can't answer the question about the other coil, but if you have a good fuel supply and your engine is failing as you say, then your ignition coil has had it, it is going open circuit when it gets hot or even shorting out between the windings.


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## Bob Driver (Nov 1, 2017)

Coils come in all different resistance specs.... As you know the P218G is an electronic ignition and the B43 is old school points. I don't really know, but the resistance through the primary and secondary windings probably aren't the same. The B43 coil would probably work to check a "No-Spark" condition, but I would think it will heat up pretty quick running with the P218G electronic triggering. Electronic coils get an impulse from a triggering device, standard points just switch the ground side of the coil on/off to fire it. Only way to know for sure would be to compare the two coils primary/secondary resistance with a DVOM, because you're probably going to have a hard time finding the resistance specs for your P218G coil on the internet to do a stand alone test on just it. That dual lead P218G coil usually only runs around $20 on Ebay.... Sten's # 166-0820


Coil test with DVOM


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## Powermatic66 (7 mo ago)

Well, replaced the coil, and that’s not the problem. Tractor starts and runs great when cold. Then after about 5-10 minutes of mowing, dies and won’t start until it cools down a bit. Can the ignition module act flaky with heat? I hate shooting the parts cannon at this thing! Especially when the module is $200! Thanks for all the input!


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## Bob Driver (Nov 1, 2017)

Man that's an Onan..... There's the usual "parts cannon", then there's Onan. That's more like shooting million$ cruise missiles at it, they aren't even laser guided with that electronic ignition, and you have to wait for Raytheon to build some parts for that missile.

Are you sure it's and ignition problem when it quits and not fuel. Does it die immediately(like you turned the key off), or does it kind of sputter/shutter and the die? Instant is usually ignition, sputter/shutter is usually fuel (bad pump, collapsing 30+ year old fuel line, semi-plugged filter/tank screen)

To determine fuel, or ignition, I'd run a couple of spark plug testers in it. When it acts up, crank the engine to see if the spark has dropped out. You already know it's not the ignition coil, so that would point to the crap under the flywheel. 

Harbor Freight Ignition Tester


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## Dan1050 (Jan 3, 2020)

I just went through the same problem recently with my 318 (Onan B43). It would sputter and die after 5 - 10 minutes and restart the next day and repeat. I cleaned the carburator, and pulled the fuel pump out (you don't have to pull the engine, if you're patient and carefull, you can remove the back screw through a hole in the fire wall) and took it apart and cleaned the sediment out of it. In doing so, I discovered that the vacuum/pulse line from the crankcase to the fuel pump diaphragm was cracked and brittle. All this after pursuing the electrcal parts cannon route. Hpoe this helps.


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## Bob Driver (Nov 1, 2017)

Dan1050 said:


> I just went through the same problem recently with my 318 (Onan B43). It would sputter and die after 5 - 10 minutes and restart the next day and repeat. I cleaned the carburator, and pulled the fuel pump out (you don't have to pull the engine, if you're patient and carefull, you can remove the back screw through a hole in the fire wall) and took it apart and cleaned the sediment out of it. In doing so, I discovered that the vacuum/pulse line from the crankcase to the fuel pump diaphragm was cracked and brittle. All this after pursuing the electrcal parts cannon route. Hpoe this helps.


Once again, correctly determining if it's fuel, or ignition, reduces by 1/2 the number of rounds you have to fire through the parts cannon. First thing you need to know when accurately firing any cannon is the azimuth to the target.


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## Powermatic66 (7 mo ago)

Thanks again for the replies. I dies instantly. I’ve quickly pulled the plugs and no spark, and I’m pretty sure I still had +12v on the positive post of the coil. I wondered if I could hook up a small 12v lamp between the pos and neg of the coil and monitor the “flashing “ while the mower is running. This might tell me if I’m missing the trigger voltage from the ignition module when it dies. Thanks again, and hope everyone is staying cool.


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## Powermatic66 (7 mo ago)

Just an update on my ignition problem. I ended up catching the problem checking the ignition module before and after the tractor warmed up. When cold, module measured between 1 and 12 vdc. Then ran the engine until it quite. Quickly pulled the plugs and checked it again. This time it was stuck on 12vdc. Continued to bar the engine over until it cooled down, and the correct signal came back. Ordered a new module, ring, and insulator directly from Cummins for $180 including tax and free shipping. Thanks again for you input.


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## Bob Driver (Nov 1, 2017)

_"directly from Cummins for $180 including tax and free shipping" _

Yep.... That's definitely an Onan part. My all-time favorite Onan ignition part is their 166-0842 ignition rotor. They use it on generators and it mounts to a stub on the crankshaft that drives the generator unit. They'll develop a hairline crack on the mounting collar. Idles fine, but when the engine speeds up, the crack widens from centrifugal force, and throws the timing off. Ignition tester still flashes, just at the wrong time. You gotta be old school to know Onan has a timing port in their blower shroud, even on their electronic ignitions..... You'll be lucky to see the crack on the collar and of course you have to split off the generator section from the engine to change that cheap plastic rotor they sell for $40+


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## Dan1050 (Jan 3, 2020)

Bob Driver said:


> Once again, correctly determining if it's fuel, or ignition, reduces by 1/2 the number of rounds you have to fire through the parts cannon. First thing you need to know when accurately firing any cannon is the azimuth to the target.


You are correct. What fooled me was when I cranked the engine, there was plenty of fuel getting to the carburator (I pulled the fuel line off the carb and pumped the fuel into a container). I pulled the top off the carb to check the float and the bowl was full of fuel. Live and learn.


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## Bob Driver (Nov 1, 2017)

Accurate trouble-shooting skills takes years to hone. It's what separates the skill levels/pay grades on a shop floor. Although I have seen 20 year master mechanics that weren't worth a damn at it, but they were experts at building transmissions and engines. People can bitch all they want about modern electronic engines, but a scanner/laptop has made it a whole lot easier to trouble-shoot problems. Modern engines, transmissions, ABS systems are way more complex and sensors are way to expensive to be guessing. 

That's added a whole new dimension to training mechanics. It now takes a few years to train a guy to get good with a scanner/laptop diagnostic software. Older guys (50+) usually don't want to go through the learning process, so it's a huge opportunity for a younger guy to move up quickly in a shop. If they are coming out of a decent voc-tech program, you don't have to explain how all the sensors function. 

Best mechanic trouble-shooting line of all time in a movie came from Karl Childers in Sling Blade..... "It's outta gas"


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