True, but I was thinking more along the lines if timing getting changed after it warms up or something. When the plug isn't fouled it fires right up, but only runs for a short time before flooding itself out. I guess I'm grasping because I'm running out of stuff to replace.
Onan Generator Over Fueling Issue
- Thread starter CWI-Guy
- Start date
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Yes, it does give me codes. 3-6 and 3-4 I believe. I looked them up when I was getting them and one was shutdown without command (usually fuel delivery system failure) and the other was low rpm / voltage. It's usually 3-6. The 3-4 rpm one only comes up once in a while after I get it going for a minute and it starts hunting rpm really badly.
I'm not sure the year of the generator, but it's in a 2016 Gulfstream. I believe it's the original one, so I would guess close to around there... I put a picture of the tag on an earlier post, not sure if you would know by the serial number or not.
I have not checked fuel pressure, only flow. It seems to flow well. I try to pick up a gauge and see how much pressure it's making at let you know.
DonTom
Well-known member
I hope you know to ignore the first 3 blinks as being an error. It only means you do have an error and to check the codes by hitting the "prime" switch on the genny to get the two-digit codes. IIRC, just hit "prime" once and get the two-digit codes when you have the three blinks.
Codes such as over or under frequency will shut down the genny, so you have been chasing an engine problem that probably doesn't exist at all.
The control board will shut down the genny when you have errors, so perhaps your RPMs are out of spec so the control board shuts it down to make your it doesn't damage any equipment by being way off frequency.
Be 100% sure of what those codes are and then we will go from there.
-Don- Reno, NV
Yes, the first three means error. I get three then six after hitting prime/stop. It repeats the three then six. All this started after it sat for a while so I figured the fuel went bad and followed that rabbit hole. Along with the code I was certain that was it. But now I have no clue. I'll grab another plug tomorrow and let it do its cycle just to verify again. However, it's thrown this particular code a lot. The three then four code has only happened a couple times after it starts running bad. I appreciate the help! I'll let you know what it says tomorrow afternoon...
DonTom
Well-known member
OIC, You got the only code that shows the engine shut down by itself, not from the control board at all. So ignore my previous post.
So you're on the correct path. Good luck.
-Don- Reno, NV
It starts, runs for a few minutes, hunts for a minute and dies. No smoke. Pull the plug and it is full of fuel. Not just wet, but you can pour the fuel out. I haven't put a clear line on it, but I have pulled the line and there is good flow, not sure the pressure. I'm going to try and figure that out thus weekend. Once it starts to hunt, I can pinch the fuel line a bit with pliers and it starts running better. Then it starts to starve and I let it go. There seems to be no happy medium. This is the second carb giving the exact same issue, so it leads me to believe it isn't the carb...
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DonTom
Well-known member
Could be a weak spark.
I test for spark with an adjustable thingy, not the ones that only flash and don't tell you much. The one in the above link can measure the spark voltage.
-Don- Reno, NV
Gary RV_Wizard
Site Team
Since the cylinder is literally full of fuel, it seems the needle valve in the carb is wide open and pouring in fuel under pressure. The amount of fuel you describe would seem to be more than could be explained by faulty ignition, i.e. a flooded cylinder vs a merely wet plug electrode. And you repeatedly state there is "good flow", but a 4k Onan doesn't suck that much fuel. I'm surprised there is much visible flow.
The "why" is more difficult to get a handle on. You already tried a new carb, so the remaining possibilities I can think of...
The "why" is more difficult to get a handle on. You already tried a new carb, so the remaining possibilities I can think of...
- Crud in the fuel keeps jamming the needle valve open
- Excessive fuel pump pressure overwhelms the float in the carb. I think it's supposed to be a max of 3 psi?
DonTom
Well-known member
Could the "hunting" just be the control board trying to put the RPMs back where it belongs?
-Don- Reno, NV
Gary RV_Wizard
Site Team
It's a constant speed generator so it has a simple governor intended to maintain the required rpms. As soon as that cylinder starts to falter, the governor opens the throttle further to bring the speed back up. In this case, that probably exacerbates the excess fuel problem, but it's the only thing a simple carb system can do. If it were fuel injected, the story would be different.
DonTom
Well-known member
If it were fuel injected, I doubt it would have this problem at all. IMAO, the Onans are an ancient design. 1950's technology even in their newest gennies.
-Don- Reno, NV
DonTom
Well-known member
If it ain't too much trouble, can you explain better how that "simple governor" works?
A mechanical thingy? I take it the control module only measures the frequency and shuts it down when way off.
-Don- Reno, NV
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Gary RV_Wizard
Site Team
It's a newer model Onan so probably not strictly mechanical, but I don't know if it would be measuring RPMs or throttle vacuum or whatever. The simplicity is the basic design - if the engine speed is dropping, open the throttle until it gets back where it needs to be. Or dies trying. There are Onan service manuals available to learn more.
I have the manual with no resolution that jumps out at me anyway. I did pick up a fuel pressure gauge. Haven't got to testing it yet. Maybe tomorrow, I'll update with pics of fuel pressure. I'm pretty good with small engines whether they're two or four stroke. Build motorcycles, scooters, and hot rods for fun. This engine is stunping me because all mechanical parts are doing their job (as far as I can tell). I lean towards electric because it's not my wheelhouse and I think all the mechanical side is operating properly.
Gary RV_Wizard
Site Team
The fuel pump on a small engine with a float-type carb isn't there to provide fuel pressure. It would be more accurately described as a lift pump, there to drag fuel from the remote tank and make it available at the carb inlet. Not PUSH it in, just keep an adequate supply available so the float reservoir doesn't run dry. As I recall, Onan says a MAX of about 3 psi. That's probably covered in the service manual.
udidwht
Well-known member
Once you get the manual for your model look up the choke setting procedure. I believe you stated earlier it stays open even after running awhile. As a result it's flooding.
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DonTom
Well-known member
Open? Or did you mean closed? "Open" means choke is not being used. Closed means closed to air to get a richer gas mixture.
-Don- Reno, NV
udidwht
Well-known member
The addition of air to fuel will lean the mixture out.
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