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Jess

518H 18HP Onan

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Hello, again,  I'm back on the same old horse !  Started to try one more time to get my mower running for more then 20 min. This time I pulled the flywheel and replaced the stator even though I got the same OHM reading on my original stator as the new one. I have not put the fly wheeI back on yet . Do you remermber t he torque it should be ? I don't remember after putting the new ing moduel in . I have a new rectifier on order and am weighting to put that in. It still looses spark and dies after 20 min. Could it be something in the wireing harness ?  I thought I would try and get it going again this summer . I have put so much time and money in it already

  I hate to give it up for parts after having it over 30 years .

 Hope you are having a good summer !

   Thank you for your time as always

 I don't know how to go back to all of the original post that I had regarding to this same issue ?  I hate to repeat all of my information ?

 Jess

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I was looking back over your old post.  You said you were loosing spark after 20 minutes of running.  Also, I think you replaced the ignition module and coil without any improvement.

 

Tracing this kind of problem is tricky.  What I would suggest is to make sure you have 12 Volts to the coil when the tractor quits. If yes, your problem is in the coil, module circuit.  If you do not have 12V to coil then you have a wiring, switch or relay problem.  A simple thing to try is to run a wire from the 12+ post on the battery to the positive terminal on the coil and run the tractor.  If that solves your problem then you have an issue with the wiring, switch and relay circuit.  If not then you have a coil, module, plug problem.  Easy enough to try, but if you do this, remember that your ignition switch will not stop the tractor, you will have to remove the jumper wire from battery.

 

You said you replaced the sator and are considering the rectifier.  They are part of the charging system and won't help your 20 min problem unless your battery is very low.  When it quits, will the tractor turn over.  If yes your battery is probably OK.

 

Hope this helps a bit.

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Mine would shut off ..... 9-pin connector.

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  . I just came in from putting it back together . New rectifier came today . So as of now I have installed stator ,new  rectifier, coil, ignition module plugs, wires, key switch , starter solenoid  battery , I ran a weir from the new  battery positive to the coil last time when I stated to try an figure out why this is happening. I cleaned all of the wire connectors many times . Like I have always posted , it starts right up and runs like a champ . You could almost set your watch by it  20 min and it starts to break up and dies , check spark to plugs , no spark .

    Thank you for your time

  It always cranks , when it dies, and I found out that I have to pull the jumper to get it to stop . Is there a way to bypass all of the harness and just wire it so basically it will just run or is running the jumper from the battery to the coil post doing just that ? I have owned this since new back in 1986 and other then just general maintenance when this started to happen I never had any problem with it . Always been a great machine for over 30 years .

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I remember someone had suggested the 9 pin connector some time ago . I know I had checked it back then but don’t remember what I did . It was in that harness Molex thing? How would I go about checking it ? I kind of slip a bit in my doing things 20 times over again.

     Would the jumper from the battery to the coil bypass it ?
                 Thank you

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I would do a visual examination of that 9 pin connector.  Look for burned posts and melted or black plastic.

Yes, a battery to coil jumper will bypass the 9 pin connector.

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When I had looked at the main connector to the harness it all looked good . I flushed it with some electrical cleaner and put some of that dialectic Lub on it as well .I also was curious about the new rectifier I installed today, There is one bolt that holds it down to the cover where it is mounted and 1 black wire that is also connected to that same bolt . Is this the way it’s suppose to be?  I went and checked my 520H and it has the same rectifier but no wire running to that bolt ? I don’t think that somewhere along the way I just bolted a wire to the rectifier ? But over time I might have slipped up ? I did try and just take it off and taped it up but there was no change in anything . My volt meter always reads over all the way high ?  I think the meter might be N/G as when I read across the back where the wires are hooked to it I’m getting around 14-1/2 V  . and it reads high even when I just turn the key on , not even running ? I will hook the jumper back to the battery and coil and run it till it dies again as I have not done it this year yet ,
           Thank you
  

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I was reading about the trigger ring ? Is this something that might be the problem or maybe a bad sensor of some type ?  Just grasping ?

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I'm not sure about the black wire on the rectifier.  Usually a black wire is a ground.  Running it to the bolt should be fine, but it is probably OK with it taped off.

 

Check your volt meter across the battery posts.  With the tractor off it should read about 12.5 volts DC.  With the tractor running it should be about 14 volts DC.

 

BTW, there is a nice procedure in the manual for checking the rectifier/charging system at the rectifier.

 

Hope that helps.

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That wire is the ground for the hour meter. Some Onan's have a double oil pressure switch that signals the low oil pressure light when pressure is low and grounds out the hour meter when it is up to pressure.

 

This is to prevent the hour meter from running if the key is left on with the engine off.

 

My machines are wired both ways depending on year.

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So if I trace this black wire from the rectifier bolt it should go back to the hour meter ?  All of my safety switch's check out OK . When I press the test button on the dash the lights all come on. If I had a bad sensor would this shut the tractor down after running 20 min  and not show a light on the dash ? When I let it cool down it starts right up and runs like new .  This is like 2 –1/2 years I've been trying to figure it out. When I called the only mower shop in my area last year they told me all they could do is just start replacing parts like I've been doing ! Don’t know how much more there is to replace other then sensors ?
  Not much help around here .

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Jess

 

Here is what I would do.

Disconnect the pink wire from the voltmeter. Replace it with a jumper wire long enough to reach the yellow wire on the seat switch but don't connect it to the seat switch yet. Connect it to the coil (+) terminal.

This way you will instantly know if you have power to the ignition coil when the engine quits or you may see it faulter before it quits.

 

If in fact you loose voltage at the coil when the engine quits move the jumper from the coil (+) to the yellow wire at the seat switch. (The reason for the long wire)

Run it again. This time if it quits and you still have voltage on the yellow wire that circuit in the 9-pin connector has failed.

 

Next step

Remove the jumper from the voltmeter and hook the pink wire back up so the voltmeter works. Take this end of the jumper and connect it to the coil (+) terminal. This will bypass the ignition circuit in the 9-pin connector. Try again.

 

Garry

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  I will give it a try this morning , I don't think I have a yellow wire to my seat switch . I know my 520 does .

                    Thank you

  Jesse

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Actually, connect the volt gauge directly to the + on the ignition coil itself with a jumper will tell you if it has power at all times.

 

My 520-HC was doing exactly as you describe and a new ignition module fixed it.

 

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The ignition module was the one of the first things I replaced at a cost of almost $200 bucks , some of these parts are out there !

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I hope you did not get a bad one for that price.

 

Did you reinstall the plastic shim/spacer under it ?

 

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Yes  I did ,It was a thick black plastic ring /spacer  What is a trigger ring ? I'm working on it now and I just took the 2 wires off of the volt meter and hooked 2 jumpers to the battery post and the meter still reads all the way over (high)  I now have a jumper hooked from where the pink wire was on the meter to the positive pot on the coil and am going to and run it till it dies . Which I know it will as always . When I turned the key to on with the jumper to the coil I got the same reading to the meter (High) would it make a difference if those 2 wires to the meter were reversed ?

   I don't know how this thing hasn't blown up yet ! If there was a way I could post a video to this when it happens I would. I am not very tech savvy .

  I don't think there was anything wrong with my original ignition module as this problem has continued . I bought the new one from a reputable seller that had sold a bunch of them at that time .

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Volt gauge should read battery voltage of 12-13 volts when connected to the battery or the coil with the key on.

 

If it reads different or pegged, gauge is bad.

 

Polarity is important and should be marked on the back of the gauge.

To really make it simple, connect a test light to the coil positive and it should stay on when the engine is running.

 

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This is where I'm at right now. When it died  the other day I  tried switching back from the Harley coil to the original Onan coil to see if it would restart . It did not so I figured I would just go back to my original coil as it was still mounted in the whole where they are and I had the Harley coil mounted above it so I couldn’t get to the Onan without taking it off. Since it didn’t make any difference I left the Harley off and am back to working with my Onan coil. My volt meter on my 518H has 4 studs coming out of the back the black wire looking at it from the front of the gauge is mounted to the top right stud and the pink wire is mounted to the bottom left stud. Like I said the gauge is always pegged . I don’t see any positive or neg mark on the back , maybe if I take it out of the mounting bracket there is something?  I looked at my 520 Volt gauge and the black wire is mounted to the top left  stud and there is a pink and a yellow mounted to the bottom left stud ?  This morning I disconnected the pink wire from the Volt meter and ran a jumper to the positive side of the coil. When I turned the key on it was still pegged . When it's running it reads around 14 -1/2 volts to the meter So I ran and mowed with it and it ran for almost 45 min !!!  That is the longest I have had it running . When it died it started to backfire as it does just before it dies but the volt meter never changed ?  Stayed pegged !  My fuel filter stays full and I know I'm getting fuel to the carb. Like I said when it runs , it’s great and purrs . Now if I weight like 40 min it will start right up and run like new ?  I don’t know should  I run a jumper from the battery positive and the coil positive again .  But I do know it wont start until it cools down ?  Maybe it ran longer today because the weather is rainy and cooler ?
 
8 hours ago, gwest_ca said:

Jess

 

Here is what I would do.

Disconnect the pink wire from the voltmeter. Replace it with a jumper wire long enough to reach the yellow wire on the seat switch but don't connect it to the seat switch yet. Connect it to the coil (+) terminal.

This way you will instantly know if you have power to the ignition coil when the engine quits or you may see it faulter before it quits.

 

If in fact you loose voltage at the coil when the engine quits move the jumper from the coil (+) to the yellow wire at the seat switch. (The reason for the long wire)

Run it again. This time if it quits and you still have voltage on the yellow wire that circuit in the 9-pin connector has failed.

 

Next step

Remove the jumper from the voltmeter and hook the pink wire back up so the voltmeter works. Take this end of the jumper and connect it to the coil (+) terminal. This will bypass the ignition circuit in the 9-pin connector. Try again.

 

Garry

 

Do you mean connect a jumper from the yellow wire on the seat switch to the positive side of the coil ?

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Also when It died this time I read from the battery Neg post to the + coil post and I had 13 Volts with the key turned on?

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2 hours ago, Jess said:

 

Do you mean connect a jumper from the yellow wire on the seat switch to the positive side of the coil ?

 

Yes. That would bypass the ignition circuit around the 9-pin connector.

 

Garry

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If I just run a jumper from the Bat pos to the coil pos would that do the same thing ?

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jess

in my opinion using the harley coil

could have FRIED you new ignition module.

thank you. boomer ( the used onan engine parts guy,

also NOS and new )

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