Fuel Pump on the 520

[bo dawg 476]

Does the fuel pumps on the Onans act up before going completely bad? The engine will run great for a few mins or may run for 1/2 hour or longer, and then it will shut down like turning the key off. Hard to get back started again. But theres always gas in the filter every time I look to see.

 

Edited June 29, 2018 by bo dawg

[Shynon 7,435]

Are you sure it's the fuel pump, mine would shut off and I found it to be a bad 9 pin connector. Next time it happens open the hood and wiggle the 9 pin connector and try starting it. 

[bo dawg 476]

No I’m not sure that’s why I was wondering how a fuel pump acts before it dies. 

[cleat 4,936]

Failing ignition module could also cause this.

 

 

[Cee245 753]

Have you done any recent maintenance to your tractor?

 

I replaced the ignition coil to fix an identical issue on my 97 416h.  It has the "little brother" p216 Onan compared to the 520's p220 Onan.  

 

After replacing the ignition coil. My 416 still shut down after mowing on warm days.  

 

THAT problem was I forgot to reinstall the heat shields covering the exhaust thus causing a vapor lock.

 

Good luck

 

Cory

[lynnmor 6,762]

These things get heat sensitive with age.  Next time you have a shutdown or no start, check the spark immediately, because it may begin to function as soon as the temperature drops.  Just stick a spark plug wire on a spare plug for a quick test.

[bo dawg 476]

It was running bad, had to choke it to run so I took top of carb off and cleaned it out, full of crap. Now it runs really good at high and low idle but now I have this this problem. 

In my previous post about the carb issue, I stated that before I took the carb apart I had the key just in run position (not running) to see if lights would work and when I turned key back off it made a loud like back fire noise. Scared the crap out of me, and done it a couple more times when I would repeat turn key on turn key off. I was scared to do it. Eventually it quit doing it and then I took carb apart.

[lynnmor 6,762]

The ignition module (trigger), that I linked to above, interrupts current to the coil to cause a spark, the key switch will cause a brief interrupt as well causing the spark plugs to fire. See page 8-2 for testing ignition. manual

[cleat 4,936]

I wonder if that is why Onan puts a condenser on the positive terminal of the coil, to prevent this.

 

One of my 520's did this until I replaced the condenser and it has never done it since.

 

[lynnmor 6,762]

3 hours ago, cleat said:

I wonder if that is why Onan puts a condenser on the positive terminal of the coil, to prevent this.

 

One of my 520's did this until I replaced the condenser and it has never done it since.

 

I think that the condenser is for radio noise suppression, but if one is shorted internally, it would cause problems.  That is a good theory, and maybe it would help with misfires.  I just looked at replacing mine because of rust and couldn't believe that 99 cent part is $15.00 plus shipping now.

Edited July 3, 2018 by lynnmor

[Cee245 753]

It really sounds like you need to take the carb completely off and take it all a part and clean every port. 

I've had to do that several times with the Nikki carbs.seem very temperamental. The carbs on these Onans really need to be clean to run properly.

 

Cory

[bo dawg 476]

I took a few mins with the tester today and just done a couple volt checks at battery and then rectifier and coil. Since I'm not much of an electrical person, I think theres an issue. With the tractor off I have good volts at battery and same at the one side of coil, but the other side of coil is almost nothing. Running I get same results with other side of coil low voltage.

Now I did the same check with my other 520 that I have, which is a couple years older but same hook up. I have good voltage in/out at both post on coil. 

So does this mean the coil is bad? I don't see a condenser. 

[lynnmor 6,762]

The ignition testing procedure is in the manual.  The condenser is mounted on the air cleaner mount and connected to the + side of the coil, just follow the wire.

[bo dawg 476]

I can not find a condenser on this thing. Both wires go down in under shroud, is that where it is? Have to pull engine cover?