Distributer cap on 318 sparking

   / Distributer cap on 318 sparking #1  

Gravel7

New member
Joined
Feb 19, 2011
Messages
18
Tractor
Deere 318
Hello,
My 318 has been missing/stumbling a bit. Sometimes worse than others. I noticed a spark arching from the left plug wire to the small nut on the left of the cap. I tested and got no spark at the left cylinder. Other side looks and sparks great. The left plug must fire most of the time though because it starts right up and will run strong, then start to stumble a bit, then fine, then stumble pretty bad, etc. Here is a picture. The trouble one is blackened. And the wire for that spot is blackened and has some fabric or insulation threads or something in it.
Does this mean the cap must be replaced or might I be able to clean it up and get a new plug wire? Any idea why this happened?
Thanks for any help!
 

Attachments

  • image-1083782825.jpg
    image-1083782825.jpg
    526.7 KB · Views: 357
   / Distributer cap on 318 sparking #2  
I had a 317, so not exactly the same. But I sorta recall there's no actual distributor cap. Pretty sure you'd have to replace the whole ignition coil. If you do that, I'd get a new pair of plug wires at the same time.

//greg//
 
   / Distributer cap on 318 sparking #3  
Which engine do you have?
 
   / Distributer cap on 318 sparking
  • Thread Starter
#4  
I have a P218G with 470 hours. I was hoping the top of the coil would pop off like a cap, but no.

Yesterday I went to the dealer, got new plugs, wires and a coil. It came to $190. I was think about trying to clean that burnt contact up and seeing how she behaved with just new plugs & wires. The dealer was convinced the coil needed replacement. I decided to just do it.

After I put new brakes on my sons do kart I installed the new parts on the 318. Success!! She's running so nicely. I had cleaned the carb and changed the fuel filter and line from the filter to carb as part of the trouble shooting. I should have checked spark first... Such an easier place to begin. But, the carb appreciates the cleaning anyway.....had been many years.

I wonder what happened to begin with? Did the coil just have enough and fail. I am hoping that there isn't some other issue that needs correcting that made the coil go. I don't have a total understanding of the ignition system and don't want to buy another coil.
 
   / Distributer cap on 318 sparking #5  
I would replace the spark plug wires first. Thats more than likely the problem.
 
   / Distributer cap on 318 sparking #6  
Ok, well the first thing would have been to try swapping plug wires if they'd reach. If not, get one or both new wires. If that didn't work, then the coil was likely bad.

Just so you know for future reference, both cylinders fire at the same time on those engines. Its just that one of the cylinders is on the ignition stroke and the other is on the exhaust stroke so the spark doesn't do anything. It's a great design; nice and simple.

Glad it's all set.
 
   / Distributer cap on 318 sparking #7  
I wonder what happened to begin with?
Ravages of age. On-road ignition components have to be replaced in time as well. In your case, it was almost certainly a compromised spark plug boot that - over time - permitted dust and moisture to accumulate in that side of the coil. If you peel back the boot at the coil end of the plug wire, you'll also probably see rust underneath the black. The metal on the wire end rusts away, leaving more room for moisture, creating better condition for spark gapping. A self-propagating situation.

You can test the coil by cleaning the carbon out of the coil hole and temporarily installing a known good plug wire. You might get lucky and get by cheaply with just one new plug wire. Technically though, you'll end up with two different spark resistance values - which is why they should always be replaced in matching pairs/sets. But it's my bet that the coil's on its last legs too. That being said, you can save money by purchasing aftermarket parts from someone other than the dealer.

//greg//
 
   / Distributer cap on 318 sparking #8  
Just so you know for future reference, both cylinders fire at the same time on those engines. Its just that one of the cylinders is on the ignition stroke and the other is on the exhaust stroke so the spark doesn't do anything. .
Didn't know that. My 317 had the infamous Kohler, as opposed to this Onan. I can see where the Onan spark wouldn't have anything to burn on the exhaust stroke. But doesn't that also mean the spark timing is such that the coil must spark twice per four-stroke evolution. I mean, after sparking on the exhaust stroke - it clearly has to spark again on the compression stroke. Right?

//greg//
 
   / Distributer cap on 318 sparking #9  
greg_g said:
Didn't know that. My 317 had the infamous Kohler, as opposed to this Onan. I can see where the Onan spark wouldn't have anything to burn on the exhaust stroke. But doesn't that also mean the spark timing is such that the coil must spark twice per four-stroke evolution. I mean, after sparking on the exhaust stroke - it clearly has to spark again on the compression stroke. Right?

//greg//

Yep, but it's a simple and effective design. No distributor. I would like to understand why the P218 was ever discontinued. Fabulous engine. And on a fabulous tractor too!
 
 
Top