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floridaroom5

Gasoline In Generator Crankcase: Onan 5500

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Good morning. We just had a new control board and carb installed on our Onan 5500 a month ago, I ran the generator for an hour or so then shut it down when we arrived at Jekyll Island Campground.

When we returned home and parked the MH in the driveway for cleanup I noticed an oil leak under the MH from the generator area. I pull the cover and checked the oil in the generator and it was running out of the fill port when the cap was removed.

I drained oil from the crankcase and noticed the smell of gasoline in the oil. The MH is a 2013 Bounder 35K. and the generator has approximately 150 hrs.

Any ideas on possible causes.

Thank you.

Thomas

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That is a good indication of a bad fuel pump diaphragm. If the pump is attached to the engine and operates with a lever from an internal cam inside this is where the fuel will come from. Only a guess. If it has an electric pump mounted externally it is not the source.

Bill Edwards

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Thank you, another WAG, would the main fuel tank vent not working properly and pressurizing the system cause gasoline to enter the genset crankcase. I have tried talking with the Ford techs and no one can tell me the system should be pressurized or not.

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What year is your coach? here is how it works; If there was a problem with the coach your service engine soon light should illuminate. My guess is its a problem with the generator. When you fill up the coach do you top off the tank? I have heard of problems when that happens, it can introduce fuel where its not supposed to be. Just in case you wanted to under stand the system better here is how it works.

Overview

The EVAP system prevents fuel vapor build up in the sealed fuel tank. Fuel vapors trapped in the sealed tank are vented through the vapor valve assembly on top of the tank. The vapors leave the valve assembly through a single vapor line and continue to the EVAP canister for storage until the vapors are purged to the engine for burning.

All applications required to meet on board diagnostics (OBD) regulations use the enhanced EVAP system. Some applications also incorporate an on board refueling vapor recovery (ORVR) system. Refer to the Workshop Manual Section 303-13, Evaporative Emissions for vehicle specific information on the description and operation of the evaporative emission system.

Enhanced Evaporative Emission (EVAP) System

The enhanced EVAP system consists of a fuel tank, fuel filler cap or capless fuel tank filler pipe, fuel tank mounted or inline fuel vapor control valve, fuel vapor vent valve, EVAP canister, fuel tank mounted or fuel pump mounted or inline fuel tank pressure (FTP) sensor, EVAP purge valve, EVAP check valve (if equipped), intake manifold hose assembly, EVAP canister vent valve, PCM and connecting wires, and fuel vapor hoses. The enhanced EVAP system, including all the fuel vapor hoses, can be checked when a leak is detected by the PCM.

1. The enhanced EVAP system uses inputs from the engine coolant temperature (ECT) sensor or cylinder head temperature (CHT) sensor, the intake air temperature (IAT) sensor, the mass airflow (MAF) sensor (if equipped), the FTP sensor and vehicle speed to provide information about engine operating conditions to the PCM. The PCM uses the fuel level input (FLI) and FTP sensor signals to determine activation of the EVAP leak check monitor based on the presence of vapor generation or fuel sloshing.
2. The PCM determines the desired amount of purge vapor flow to the intake manifold for a given engine condition. The PCM then outputs the required signal to the EVAP purge valve. The PCM uses the enhanced EVAP system inputs to evacuate the system using the EVAP purge valve, seal the enhanced EVAP system from the atmosphere using the EVAP canister vent valve, and uses the FTP sensor to observe total vacuum lost for a period of time.
3. The EVAP canister vent valve seals the enhanced EVAP system to atmosphere during the EVAP leak check monitor.
4. The PCM outputs a duty cycle between 0% and 100% to control the EVAP purge valve.
5. The FTP sensor monitors the fuel tank pressure during engine operation and continuously transmits an input signal to the PCM. During the EVAP monitor testing, the FTP sensor monitors the fuel tank pressure or vacuum bleed up.On some vehicles, a vapor blocking valve is used to isolate the fuel tank from the rest of the EVAP system for more efficient canister purging.
6. A valve inside the fuel tank mounted fuel vapor tube assembly prevents liquid fuel from entering the EVAP canister and the EVAP purge valve under any vehicle altitude, handling, or rollover condition.
7. On turbocharged engines, the EVAP check valve prevents boost pressure from entering the EVAP system.
8. On turbocharged engines, the turbocharger creates boost pressure in the intake manifold.
9. On turbocharged engines, an EVAP ejector is used to create a vacuum in the purge line during boost conditions. When in boost conditions a percentage of the boost pressure is applied to the EVAP ejector to create a vacuum. This vacuum draws purge vapors through the EVAP ejector into the intake air system upstream of the turbocharger.

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11 minutes ago, floridaroom5 said:

Thank you, another WAG, would the main fuel tank vent not working properly and pressurizing the system cause gasoline to enter the genset crankcase. I have tried talking with the Ford techs and no one can tell me the system should be pressurized or not.

Thomas, To meet EPA requirements, the fuel tanks are required to have a vapor  recovery system cycle. This system is often vacuum or electrical control so the vapor is cycled back into the engine intake manifold.

When you remove the gas filler cap and there is pressure in the tank, one can often smell or even feel the pressure release.

Rich

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Hear is my SWAG. There is enough fuel pressure to overcome the float/needle valve and letting fuel to run into the cylinders and into the crankcase. Perhaps the electric fuel pump isn't shutting off or you are getting some kind of pressure from the RV system. 

Bill

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Who replaced the carb? If done by a professional, I would return to that facility with complaint. Could be wrong carb., or a faulty one, especially if this is the first time that same symtoms have appeared.

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I would also expect that the carburetor needle valve is not seating properly.  Make sure that that you pull the spark plugs and       rotate the engine before starting to make sure you don't have a cylinder full of fluid () that could cause a hydraulic block.

Jim

 

 

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I  would suspect the carb installation. If not done correctly, it can introduce fuel into the crankcase. I had this happen to mine in my 5th wheel before I sold it. I had a mechanic friend that told he could replace the carb for me. Bottom line the generator ran pretty well, but it filled up the crankcase with fuel. I took it to Onan and they replaced the carb a second time. It was perfect after that. 

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if fuel pump is not electric....then 90% of the time this is fuel pump.  pump uses a diaphragm and check valves to use the crankcase pressure fluctuations to pump fuel. diaphragm ruptures and fuel leaks into crank case.  replacement here...

https://flipmfg.com/products/fuel-pump-2-pack-fits-cummins-onan-generator-149-1982-149-1544-149-2191

 

might be better to consider upgrading to electric pump.... onan has changed newer ones to electric

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Thanks for all the info, we returned from our trip to Michigan and I did not run the gen set at all while on the road. Yesterday I returned the Bounder to the RV shop that replaced the carb and made the aware of the issue. The carb came from the local Onan dealer and they will replace it with and new one. My concern is I ran that gen set for about 2 hours prior to realizing there was a problem with the fuel in crankcase, what are the chances this has caused other damage to the generator. Thank you, Thomas. 

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I had the same problem with an older Onan 6 KW gen-set. It was a two cylinder engine, and one cylinder was not firing. This cylinder still continues to draw in fuel, but it will run into the crankcase instead of being burned and going out through the exhaust. I found the oil level a full inch above the FULL mark!

I am much more familiar with small one cylinder engines, and when that cylinder stops firing - the engine stops. I learned a lesson from this - when a two cylinder engine runs on only one cylinder it is not really that noticeable.

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