520 with Onan engine

[OPPOSITE2@AOL.COM 0]

My Onan engine is only running on the rear cylinder,(towards the driver) both cylinders have above 100 psi compression, I installed new plugs, coil, plug wires, and condenser, both plugs are getting a weak spark. I tried switching plug wires from one side to the other and still the same.Anybody have any idea why? Any help would be greatly appreciated. Thanks.

[gwest_ca-(File Mod) 11,389]

Welcome to Red Square

 

Ignition coils are step-up transformers. They take battery voltage of 12-14 volts and boost it to say 20,000 volts.

Make sure you are getting the 12-14 volts at the coil (+). Any less and it won't make the 20,000 volts required for good spark.

Good clean connections are key plus you have the infamous 9-pin connector which often requires attention.

There is also a condenser on the coil (+) which is not what we normally see.

[lynnmor 7,706]

 

Try disconnecting the condenser and see if that changes anything.  The normal location for the condenser is on the air filter support.

 

Maybe you have a valve sticking just enough to keep it from working at speed.

 

The front cylinder head is real easy to pull, perhaps you want to do that and see the amount of carbon and other conditions.

[oliver2-44 10,573]

Is this a new to you tractor, or has it been running good and just started having this problem. 

[OPPOSITE2@AOL.COM 0]

20 hours ago, gwest_ca said:

Welcome to Red Square

 

Ignition coils are step-up transformers. They take battery voltage of 12-14 volts and boost it to say 20,000 volts.

Make sure you are getting the 12-14 volts at the coil (+). Any less and it won't make the 20,000 volts required for good spark.

Good clean connections are key plus you have the infamous 9-pin connector which often requires attention.

There is also a condenser on the coil (+) which is not what we normally see.// Thanks for the reply back, should there be 12-14 volts to the coil when the key is just turned on? I did replace the 9 pin connector by doing one wire at the time.

 

[lynnmor 7,706]

At the top of this forum is a thread to help you with Onan ignition issues.

[OPPOSITE2@AOL.COM 0]

17 hours ago, lynnmor said:

 

Try disconnecting the condenser and see if that changes anything.  The normal location for the condenser is on the air filter support.

 

Maybe you have a valve sticking just enough to keep it from working at speed.

 

The front cylinder head is real easy to pull, perhaps you want to do that and see the amount of carbon and other conditions.

 

[OPPOSITE2@AOL.COM 0]

I tried everything everybody suggested but nothing worked. thanks to all that replied.

[OPPOSITE2@AOL.COM 0]

15 hours ago, oliver2-44 said:

Is this a new to you tractor, or has it been running good and just started having this problem. 

 

[OPPOSITE2@AOL.COM 0]

was running fine, just started running on one cylinder.

[OPPOSITE2@AOL.COM 0]

36 minutes ago, lynnmor said:

At the top of this forum is a thread to help you with Onan ignition issues.

Thanks for the info. Is there a way to print it so it is large enough to read?

[Handy Don 13,683]

55 minutes ago, OPPOSITE2@AOL.COM said:

Thanks for the info. Is there a way to print it so it is large enough to read?

I think most of those pages are from this manual in the files:

 

[OPPOSITE2@AOL.COM 0]

4 hours ago, OPPOSITE2@AOL.COM said:

 

When would you check the coil for voltage? while cranking or with the key on? I do have spark to both cylinders bit only the one will run.

[squonk 43,359]

That engine fires both plugs at the same time. Once at the end of the compression stroke and once at the end of the exhaust. It's unlikely the coil would kill one cylinder. I would look for a vacuum leak to the front cylinder , possibly on the intake manifold where the halves meet. A leak will lean out the mixture and cause it to misfire.

 

[OPPOSITE2@AOL.COM 0]

5 minutes ago, squonk said:

That engine fires both plugs at the same time. Once at the end of the compression stroke and once at the end of the exhaust. It's unlikely the coil would kill one cylinder. I would look for a vacuum leak to the front cylinder , possibly on the intake manifold where the halves meet. A leak will lean out the mixture and cause it to misfire.

 

There is no misfire on the front cylinder, It never ignites the fuel & just blows it out the exhaust. I checked the ohms between the primary + & - on the coil, it is within specs. not getting any reading for the secondary resistance from the old coil or the new aftermarket one installed. Maybe the new one is bad also? I tried switching plug wires from the front to the back thinking the coil was bad but still only the rear cylinder will run.    

[squonk 43,359]

12 minutes ago, OPPOSITE2@AOL.COM said:

There is no misfire on the front cylinder, It never ignites the fuel & just blows it out the exhaust. I checked the ohms between the primary + & - on the coil, it is within specs. not getting any reading for the secondary resistance from the old coil or the new aftermarket one installed. Maybe the new one is bad also? I tried switching plug wires from the front to the back thinking the coil was bad but still only the rear cylinder will run.    

If the intake leaks bad enough it will not fire the cylinder. Check the intake runner. They are known to leak

 

Edited May 11, 2023 by squonk

[Handy Don 13,683]

Try switching the plugs, and not just the wires?

If it isn’t spark, then it is definitely a fuel/air issue.

[OPPOSITE2@AOL.COM 0]

19 minutes ago, Handy Don said:

Try switching the plugs, and not just the wires?

If it isn’t spark, then it is definitely a fuel/air issue.

I tried switching the plugs, tried the old plugs, changed oil & filter, getting plenty of fuel because it gets pushed out of the exhaust.

[Handy Don 13,683]

4 minutes ago, OPPOSITE2@AOL.COM said:

I tried switching the plugs, tried the old plugs, changed oil & filter, getting plenty of fuel because it gets pushed out of the exhaust.

Did you switch the plug wires themselves or only switch holes at the coil. I’d want to eliminate a bad wire (or a wire shorting to ground instead of giving you a spark) as a possibility if you haven’t already.

The issue is probably fuel/air -- the concentration of fuel in the intake air, not that there is no fuel.

Edited May 11, 2023 by Handy Don

[lynnmor 7,706]

The 520-H models have a horsepower meter that is simply a vacuum gauge.   A vacuum hose runs from a fitting in the intake manifold to that meter, often they are not connected or in poor condition.  While looking at hoses, there is a small hose from the bottom of the air filter base to a vacuum switch behind the dash, if the nipple is broken off the switch the hose needs to be plugged.

[OPPOSITE2@AOL.COM 0]

3 hours ago, lynnmor said:

The 520-H models have a horsepower meter that is simply a vacuum gauge.   A vacuum hose runs from a fitting in the intake manifold to that meter, often they are not connected or in poor condition.  While looking at hoses, there is a small hose from the bottom of the air filter base to a vacuum switch behind the dash, if the nipple is broken off the switch the hose needs to be plugged.

 

I see the hose for the horsepower meter, it is hooked up, I see the hose under the air cleaner but see no vacuum switch behind the dash. What does it look like?

[Handy Don 13,683]

8 minutes ago, OPPOSITE2@AOL.COM said:

I see the hose for the horsepower meter, it is hooked up, I see the hose under the air cleaner but see no vacuum switch behind the dash. What does it look like?

Kinda like this.

The switch is capable of detecting low or high pressure, depending on the nipple that’s connected. On the Onan, it is looking for low (i.e. partial vacuum) that indicates that the air filter is clogged.

 

Edited May 12, 2023 by Handy Don

[OPPOSITE2@AOL.COM 0]

6 minutes ago, Handy Don said:

Kinda like this.

The switch is capable of detecting low or high pressure, depending on the nipple that’s connected. On the Onan, it is looking for low (i.e. partial vacuum) that indicates that the air filter is clogged.

 

 

6 minutes ago, Handy Don said:

Kinda like this.

The switch is capable of detecting low or high pressure, depending on the nipple that’s connected. On the Onan, it is looking for low (i.e. partial vacuum) that indicates that the air filter is clogged.

 

I see nothing that looks like that. should I get one or just plug the hose end?

[lynnmor 7,706]

Plug the hose, they are hard to find and expensive.

Edited May 12, 2023 by lynnmor

[squonk 43,359]

That missing switch and open hose could be contributing to your problem. K&B a vendor here has that switch for $35 shipped.

 

 

Edited May 12, 2023 by squonk