520-H starts then dies

[WheelHorse520H 708]

Hi all, I have a 1988 520-H. I’ve seen this problem half a dozen times but my test results are confusing. My 520 started up yesterday and ran for maybe 15 minutes, enough for me to warm it up and make two passes with the snow plow. Then it skipped a little and just died. First thing I thought of was the Ignition Control Module behind the flywheel. So I towed it back up the driveway with the 607 and thought about it more. I realized I had put in an aftermarket cheap Chinese ignition coil. (This was before I knew it was a bad idea.) So I got out the original (because it tested okay when I found out it wasn’t the coil with a previous issue) and the Chinese one, let them sit inside to warm up overnight to about 60 degrees Fahrenheit (the Onan service manual says 70 degrees but we don’t keep the house that warm as it’s better than the 20 degrees outside) and tested them. The OEM coil had proper resistance on the primary coil but the secondary coil had infinite resistance. The Chinese coil had good resistance on the primary but was at 21,180 ohms, but the manual says 19,800 is the maximum allowed resistance. I put the OEM coil in and got no spark, as expected, put the Chinese coil in and it started and ran with decent spark. Then the same thing happened and it died, this time after only about 10 minutes. So while it was hot I tested the control module and it went from better voltage down to about 6.4 volts instead of the 1 volt the manual says it should be at. I am letting it cool down and will see if the control module results change. My big question is, could the extra resistance in the coil cause the same problem as the control module overheating? How do I determine which is the problem, could they both be causing this issue?

 

Thanks in advance,

Andrew

[oliver2-44 10,711]

The first time you said it skipped a little then died, which could’ve a fuel thing. Check that the vent in your gas cap is open. Run it again with the gas cap slightly loose and see if it dies it again. The coil resistance will change with temperature. Others will be along to comment how much is OK. 

[lynnmor 7,814]

Since this has been an ongoing problem, it might be time to just empty the wallet and buy parts.  Intermittent electrical problems are hard to diagnose and sometimes impossible.  I have one Chinese coil that has been working for years, but they may have reduced quality lately.  I'm sure that you inspected the ignition switch and all connectors to the engine, if not, do that service first.

 

In extremely cold, I had an issue one time where the condensation inside the pulse hose to the fuel pump freeze solid, stopping the engine.  Just one more idea.

[bds1984 1,498]

53 minutes ago, lynnmor said:

 

 

In extremely cold, I had an issue one time where the condensation inside the pulse hose to the fuel pump freeze solid, stopping the engine.  Just one more idea.

 

That issue is often overlooked.  My mother-in-law had a furnace issue a few years ago that couldn't be diagnosed by the service tech.  The drain to for the a/c evaporator portion of the furnace was plugged and then in turn drained everywhere.  A tiny amount of moisture had made its way into the hose of an air pressure sensor circuit on the power vent which prevented the furnace from firing up past the glow-bar stage.  

Edited January 22, 2022 by bds1984

[WheelHorse520H 708]

3 hours ago, oliver2-44 said:

The coil resistance will change with temperature.

It was about 1,000 ohms above when I brought it in and it continued to get further and further away from the range. I will try the gas cap thing, the fuel pump seems to be pumping but a bit weak.

 

2 hours ago, lynnmor said:

In extremely cold, I had an issue one time where the condensation inside the pulse hose to the fuel pump freeze solid, stopping the engine.  Just one more idea.

I might look into that next.

I also tested the control module now that it’s cold and it was working correctly.

Thank you all for the suggestions.

Edited January 22, 2022 by WheelHorse520H

[WheelHorse520H 708]

I have made a mistake, the first time I tested the control module I misread the decimal place, it was and still is functioning correctly. The gas cap was just barely threaded on and the issue continued. So now I am going to investigate the clogged vacuum line for the pulse pump. If it’s not that either I think it’s the cheap  Chinese coil. If it was a clogged vacuum line would it run as long as it has been? Still going to look into it, just curious. Also worth noting the fuel filter was about half full the whole time it has been running.

 

Thanks again for all the suggestions.

[Handy Don 14,061]

1 hour ago, WheelHorse520H said:

Also worth noting the fuel filter was about half full the whole time it has been running

This is common. When the filter is "on its side" there is no easy way for the air trapped in it to get out. Some members install the filters vertically where they can but on the Onan, if you want the filter after the fuel pump as I do, it pretty much has to lay sideways. Electric fuel pumps have higher pressures and volumes than the pulse pump so they can sometimes fill the filter, as well.

[WheelHorse520H 708]

The pulse pump vacuum line was clear and open. I was working out there yesterday after it warmed up and died again and bumped the coil, I noticed it seemed to be a bit warm. I don’t know if it was just heat from the engine or if there was so much resistance that it heated up creating more resistance causing it to stall. Is this even possible? Just trying to narrow down the problem any way I can. @Handy Don when I mentioned the fuel filter, it was more of a “I think it is getting enough fuel” kind of statement. I know there is always an air bubble. Thanks for making sure we’re on the same page though.

[Handy Don 14,061]

It sounds like you are chasing the dreaded "intermittent."

Lousy weather for it, but I wondering if there's a way to get the meter on the coil quickly once it stalls. 

It is definitely possible to generate a lot of heat across a corroded connection with the electrical power available on a 520-H, right? So in my mind having that happen inside a coil is worth considering. BTW, coils rarely fail due to broken internal wires (from what I've read in my research) but rather due to heat-caused insulation breakdown that causes short circuits in the windings. I don't think it is an accident that the coil on the P2xx engines is situated in the cooling airflow.

[WheelHorse520H 708]

1 hour ago, Handy Don said:

Lousy weather for it,

No truer words have been said…

 

1 hour ago, Handy Don said:

wondering if there's a way to get the meter on the coil quickly once it stalls. 

Probably, if I connect it with jumper leads, let it die, shut off the ignition (disconnect the battery?) and test it. 

 

1 hour ago, Handy Don said:

BTW, coils rarely fail due to broken internal wires (from what I've read in my research) but rather due to heat-caused insulation breakdown that causes short circuits in the windings. I don't think it is an accident that the coil on the P2xx engines is situated in the cooling airflow.

I hadn’t thought about the airflow but the old coil sat down in the airflow but the new one sits in a bracket above the airflow, maybe how the problem originated.

 

The only reason I thought the coil was the extra resistance would cause unwanted and unnecessary heat, therefore creating unnecessary resistance, and more heat…so on so forth. I could be wrong though, that’s just how I see it.

[WheelHorse520H 708]

Okay, as soon as it dies the primary had 4.1 ohms … a bit out of spec, and the secondary had 21,870 ohms. Wwwaaayyy out of spec. I am going to order a new coil soon I think.

[RED-Z06 2,567]

Maybe a bad condenser?

[WheelHorse520H 708]

20 hours ago, RED-Z06 said:

Maybe a bad condenser?

Do you know how to test that? Is it to just see if it has any continuity between the wire and the case? If so I already did that and it seems okay.

[RED-Z06 2,567]

3 hours ago, WheelHorse520H said:

Do you know how to test that? Is it to just see if it has any continuity between the wire and the case? If so I already did that and it seems okay.

https://www.hunker.com/12226169/how-to-test-a-condenser-in-a-small-engine

[WheelHorse520H 708]

Does this work with a DVOM because I see one step talks  about the needle on the meter? I only have a DVOM.

[RED-Z06 2,567]

11 minutes ago, WheelHorse520H said:

Does this work with a DVOM because I see one step talks  about the needle on the meter? I only have a DVOM.

Never tried it with a dvom, testing these is probably the only reason a shop would keep around an analog anymore.

[RED-Z06 2,567]

 

[pfrederi 18,664]

I test my condensers by replacing them...They ain't that expensive.  If problem is resolved trash the original still an issue mark it good and save it...

[RED-Z06 2,567]

1 hour ago, pfrederi said:

I test my condensers by replacing them...They ain't that expensive.  If problem is resolved trash the original still an issue mark it good and save it...

Generally what i do also...theyll make you chase your tail..once you get burned (figuratively) by one you just swap em 

[lynnmor 7,814]

The condenser on an Onan may not be necessary for the ignition to work.  It is said to suppress spikes and it may be there to suppress radio interference.  I have never read about the exact purpose and it isn't part of the ignition troubleshooting in the Onan service manual.  The condenser is connected to the battery side of the coil and to ground.  I have never replaced one.  The price is about $16 each.

[Jeff-C175 7,206]

2 hours ago, lynnmor said:

It is said to suppress spikes and it may be there to suppress radio interference.

 

I always thought it's main purpose was to minimize arcing at, and thus increasing the life of, the points.

It also plays a part in 'shaping' the waveform of the spark itself.

I believe the technical term is "damped sine wave".

It's about the REACTANCE of the capacitor versus the reactance of the INDUCTOR (the coil primary)

 

Out of all the engines that I've ever owned, I can't recall once having a bad condensor.

When we were youngsters, as part of a 'tune up' we generally replaced the condensor whether it was bad or not.  

 

Not sure the engine would run without the condensor though... at least not very well.

 

 

 

Edited January 28, 2022 by Jeff-C175

[RED-Z06 2,567]

48 minutes ago, Jeff-C175 said:

 

I always thought it's main purpose was to minimize arcing at, and thus increasing the life of, the points.

It also plays a part in 'shaping' the waveform of the spark itself.

I believe the technical term is "damped sine wave".

It's about the REACTANCE of the capacitor versus the reactance of the INDUCTOR (the coil primary)

 

Out of all the engines that I've ever owned, I can't recall once having a bad condensor.

When we were youngsters, as part of a 'tune up' we generally replaced the condensor whether it was bad or not.  

 

Not sure the engine would run without the condensor though... at least not very well.

 

 

 

Its always been my experience that if the condenser fails you get a poorly running engine that quickly loses spark due to blown points.

 

Which begs the question why a breakerless Hall Effect ignition has one..

[Jeff-C175 7,206]

8 minutes ago, RED-Z06 said:

why a breakerless Hall Effect ignition has one.

 

Probably to 'damp' the sine wave.

 

 

[kpinnc 14,630]

Can't speak for Onan, but I've seen a bad condenser make a K301 run like garbage, if it would crank at all.

 

I had also never seen one fail at the time. I couldn't believe what a difference it made.

[Bill D 2,247]

Make a jumper with alligator clips.  Jump directly from the positive of the battery to the positive on the coil.  See if your problem goes away.  I had a 416 with overheated fuse holders.  It ran fine for a little while, then cut out when the connections got hot.