Onan running on one cylinder-why

[namumac1]

One carb and I have moved plugs with no change.

 

[NY_Dutch]

Post deleted, I forgot the compression question was answered in the OP.

 

[DonTom]

Let's see what has been done so far.

100 PSI on each cylinder rules out a mechanical issue.

Trading plugs, wires etc., makes no difference, problem is still in same cylinder. Rules out a spark problem.

Single carb rules out a carb problem.

Seems we have checked everything.

At this point, I would want to recheck everything already done.

Can there be a plug wire arcing to the frame somewhere, a tight spot where the wire can be pinched?

Perhaps something Intermittent, such as a valve closing when you checked but not every time?

-Don- Auburn, CA

 

[Utclmjmpr]

The first post states the compression is the same,, some how the "bad" cylinder is getting too much fuel.. Either the "bad" cylinder is getting too much fuel or. that plug is some how shorting out..>>>Dan

 

[namumac1]

If the bad cylinder was getting too much fuel wouldn't the plug be wet? This is dry and sooty.

 

[DonTom]

f the bad cylinder was getting too much fuel wouldn't the plug be wet? This is dry and sooty.

Sounds like it is probably firing, but rich, which means too much fuel or not enough air.

Even if you have already changed both spark plugs, at his point, I would reverse them and see what happens.

Or is there a way a single carb can deliver too much fuel (or not enough air) to only one side?

-Don- Reno, NV

 

[namumac1]

Updated question> Would the ignition module cause this if it was faulty?

 

[DonTom]

Updated question> Would the ignition module cause this if it was faulty?

No, because it uses a waste spark. Both plugs fire from the same source at the exact same time. Just one of the sparks on each side does nothing and the other spark fires the cylinder. Opposite on each cylinder, each time. As one fires the other has a waste spark that does nothing in normal operation.

Both valves are open on the waste spark side, so the spark does nothing on each side every other plug fire.

Could it be a bad spark plug cap or wire? Try reversing those.

-Don- Auburn, CA

 

[Aaron5er]

I'm not a mechanical tech but....
What's the possibility the intake manifold is cracked close to the cylinder and not allowing suction of fuel?
Clogged intake?
Blown intake gasket?

 

[namumac1]

The compression is good and when the plug wires are reversed at the coil the misfire happens in the other cylinder.

 

[namumac1]

No, because it uses a waste spark. Both plugs fire from the same source at the exact same time. Just one of the sparks on each side does nothing and the other spark fires the cylinder. Opposite on each cylinder, each time. As one fires the other has a waste spark that does nothing in normal operation.

Both valves are open on the waste spark side, so the spark does nothing on each side every other plug fire.

Could it be a bad spark plug cap or wire? Try reversing those.

-Don- Auburn, CA

The plugs, wires, condenser and coil all replaced with no better results.

 

[DonTom]

The plugs, wires, condenser and coil all replaced with no better results.

If a cylinder has spark at the correct time, fuel, & compression it must run. That's fact.

But you say you have no spark at one side only from the same coil. Could there be a short to ground somewhere on the plug wire? Have you checked for spark on the bad side withOUT using the sparkplug as an indicator? Can you take a photo of where the spark plug is on the bad side?

Does the plug fire when outside the engine?

-Don- Auburn, CA

 

[namumac1]

Have changed the plugs twice, the wires are new. there is no bad side because it changes when the wires are reversed. If I move the plugs to the other side it makes no difference.

 

[DonTom]

there is no bad side because it changes when the wires are reversed.

Then you have a bad spark plug wire, new or not, it's not doing the job.

-Don- Auburn, CA

 

[namumac1]

Possible but it fired the same as with the old wires. I checked it with a multi meter and there is continuity.

 

[DonTom]

Possible but it fired the same as with the old wires. I checked it with a multi meter and there is continuity.

How many ohms in each wire? Check them both and compare. Be sure to move the wires a bit as you check them.

-Don- Auburn, CA

 

[namumac1]

Can't remember the reading, will have to check later cause the generator is buried. I have been around long enough to know that new parts can and are sometimes defective. I'll check that out. Thanks.

 

[Gary RV_Wizard]

Since the problem moves with the spark wire, that has to be the source of the problem, either the wire or its connections on either end. And since a new wire didn't change anything, I'd lean toward the connection at the coil end. I know you also replaced the coil, but it has to be something on that spark path.

Sometimes simply looking at it in the dark shows up a leaking spark (short to ground).

 

[namumac1]

The ignition module tested not good. The old one slid out easily but the new one is hitting on the generator cooling fins and won't slide in. Is there a trick to this? Hopefully I don't need to separate the engine and generator. Any ideas would be appreciated.

 

[DonTom]

The ignition module tested not good.

I don't see how that can be possible in a two cylinder engine that uses a waste spark. No way can the ignition module only fire the sparkplug on one side.

Either both will fire or none. It's not going to break on every other spark to make only one side fire.

-Don- Auburn, CA