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vintagez

'97 520-H no spark issue

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vintagez

Hey everyone! Thanks for checking this thread out. New here and I'll post some info if there is a new member page in the site soon. But onto my issue for now.

 

I've been doing a lot of work on this 520 I rescued from an auction in West OH this past winter. After adjust valves, decarbon, fuel lines, fuel pump, tank clean and just generally cleaning it up I ran into a no spark problem. What I did was put the tractor on a battery charger that I usually use on my car. I came back to the tractor after about 45min or so and found the ignition coil very hot. At this point I believe I was getting no spark and did verify that by pulling plugs out (typically starts right up, too).I'm kind of in a pinch and even had to push mow my yard (~.4 acre) instead of working on the tractor. Anyhow, hoping to get out tomorrow night and use my multimeter to go through some tests to see if I can pin point the issue with threads I've read over from the forum. But if anyone had any quick idea based on the hot ign module after charging I would be interested to know. Thanks and I'll post updates to this to show I actually figured it out. 

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lynnmor

:text-welcomeconfetti:

 

First, the battery charging should have no effect unless there is a fault.  Did you have the ignition switch on the whole time?

 

Information

 

Demystification Guide

 

Owners Manuals

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vintagez

Thanks for the welcome, but now that I think about it I did have the ignition switch on the whole time! 

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lynnmor

The information on testing the Onan ignition components are in the Onan manual.

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vintagez

Thanks a lot, I’ll try and go through it a little later. Hoping I didn’t kill everything. Not sure if it could be a relay or not. 
 

 

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vintagez

Only have a little time to check things out but I did run a wire from the + battery terminal to the + coil post and turn the engine over to see if that would give spark. From what I could tell it did not. 
 

I also used my multimeter and measured the - battery post to the - coil post to check that the signal was going from 12 to ~ 1v as the engine turned over. From what I could see it was not doing that. I could see the 12 but then I was getting a fault. I need to pick up a good set of alligator clips for the meter and double check this probably. 

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vintagez

B3B3ED64-033D-474B-B10E-09D7E082EA91.jpeg

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lynnmor
5 hours ago, vintagez said:

Only have a little time to check things out but I did run a wire from the + battery terminal to the + coil post and turn the engine over to see if that would give spark. From what I could tell it did not. 
 

I also used my multimeter and measured the - battery post to the - coil post to check that the signal was going from 12 to ~ 1v as the engine turned over. From what I could see it was not doing that. I could see the 12 but then I was getting a fault. I need to pick up a good set of alligator clips for the meter and double check this probably. 

 

Follow the Onan manual carefully on page 8-1 when testing the trigger module, they are getting old and failing.  Since they are expensive and difficult to replace you want to be sure that is the problem.  Also, they can work OK till the engine warms up and then quit, making it nearly impossible to diagnose.

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vintagez

Well I had some time tonight to check through 8-1 in the Onan manual and picked up a set of alligator clips for my meter. 
 

I double checked and confirmed that connecting a wire from the + battery cable lead to the + coil post did not result in spark. 
 

I then connected my meter to the - coil post and to ground. I manually turned the engine over with the ignition on. I was able to see the post go from 12V down to .9V confirming that the ignition module was working. 
 

I then checked the resistances between the - and + posts on the coil. The resistance should be between 2.9 - 3.6 Ohms. Mine was right at 3.5 Ohms. So that was in spec. 
 

I then checked the resistance between the spark plug caps at the coil. I just stuck the probes inside each hole. I was reading 0. This value I believe should have been between 14-19.6kOmhs. So with that finding, I think the coil is indeed shot. 
 

Let me know what you guys think. 

Edited by vintagez

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lynnmor

Sounds like you followed the coil test and found a bad coil.

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vintagez

Just an update. I did order the coil and a set of plugs from onanparts. Hoping I can get them by early next week and see if it puts us back in business. Will keep everyone posted and I’ll be sure to snap a few pictures. 

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vintagez

Well I got the parts in and I confirmed that the resistance was the spark issue! However, I’m not getting any fuel to spray out of the carb. 
 

i had the carb off and cleaned everything as well as I could when I did the other PM. I added a new fuel pump so I had all the fuel drained out of the lines. I now have fuel in the filter and I think up to the carb. But I’m not able to get fuel to come out. Maybe I have blockage where the fuel line meets the carb? 
 

im able to get it to fire when I pour a little through the carb and into the intake and it goes full throttle (as expected since it’s a lot of fuel). 

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lynnmor
8 hours ago, vintagez said:

im able to get it to fire when I pour a little through the carb and into the intake and it goes full throttle (as expected since it’s a lot of fuel). 

 

It should not go "full throttle" unless the throttle is wide open.  Perhaps you have the linkage in the second curve instead of the first.  Test the fuel pump by removing the hose from the carburetor and directing it into a container and run the starter.  If you have fuel pumping, then the carburetor is faulty.

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vintagez

Thanks a lot Lynnmor, I did have it in the second curve. Also, I didn’t have the needle and float attached properly. So now it idles but it’s rough. After looking more it seems the gasket where the intake meets the carb is damp. I’m guessing I didn’t tighten those bolts enough which is a real shame. I hope the issue is just that though. Had this thing apart longer than intended. I’ll report back tomorrow night. Thanks for the help!! 

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lynnmor

If you have been dumping a lot of fuel into the engine, an immediate oil change is in order.  With the correct type of wrench you might be able to tighten the bolts without pulling the intake.

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vintagez

Thanks for the tip, I’ll get it changed ASAP. But I had it all back apart and even painted the exhaust while I was at it. BUT it looks the the intake/carb gasket is still getting damp and it’s still surging. But it does fire right up.

 

tomorrow night I think I’ll take it back apart and inspect the gasket (new) and triple check it’s tight. Anyone have a torque spec for it? 

it was surging at idle and didn’t seem like much fuel was getting to it, I could tell by the filter. Hoping it’s just an air leak at that gasket. 
 

thanks for the help! 

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lynnmor
4 hours ago, vintagez said:

 Anyone have a torque spec for it? 


it was surging at idle and didn’t seem like much fuel was getting to it, I could tell by the filter. Hoping it’s just an air leak at that gasket. 
 

I don't think there is a torque spec, just use common sense.

 

You can't tell much from looking at the fuel filter, often there is harmless air in it that people get concerned about.  There is a welch plug on the right side of the carburetor near the bottom, make sure it is still there.

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vintagez

Yeah that’s what I figured and did. Not sure if the gasket has a slice or something that I missed. Hard to take a photo of it but I’ll post the one I did take of the gasket. That plug is the large brass one? I did tighten it and doubled checked it when I noticed the gasket was damp. Maybe I’ll get it tonight. 
 

 

467F0166-5DF6-4630-A305-88F7F54370EB.jpeg

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Handy Don

The Welch plug is the shiny thing directly above the idle mixture screw

.carb.jpg.a447672af41dc6026b8f0e30856522e5.jpg

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vintagez

Going to make a new topic on the engine thread for the carb issue. Thank you all for the ignition coil help! 

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