Onan Generator wil not Prime

[jeffo]

I have a 2013 Onan 5500 gas generator. I was going to exercise it today and when I hit the prime I cannot hear the pump running. It turns over fine but will not start. I assume it not getting any gas. Not sure if the pump you hear when you prime is the fuel pump that also feeds the carb after it is started. I checked all the wires that I can see, all look fine. Not sure where the primer pump is? It ran fine last month and the gas tank is full.

[jeffo]

Its a small diaphragm type pump. It is not making any sound at all now, You can normally near it from inside the RV. An Onan pump is 94.00 and a Airtex pump is 38.00. I think I will try the Airtex It is very easy to change if it does not last. However they get good reviews.

[azrving]

Is a Bendix type pump that sort of chatters until it builds pressure? Crack a line and check for pressure.

[jeffo]

I checked the voltage to the pump and I am getting 14.5 when the rocker switch is in the prime position. I read somewhere to tap the pump with a screw driver handle but it did not work. I guess I will replace the pump.

[Bobbo]

Does it do the same thing if you press and hold the start button that is located on the body of the generator itself?

[azrving]

jeffo wrote:
On mine the faults are read by counting the flashes on the rocker switch. I am not reading any faults. My manual does mention an over cranking fault (if engine does not start after 30 seconds) but no mention of over priming. Tomorrow I will check the voltage to the fuel pump, it should be fused somewhere. Thanks for posting the link to the service manual. It should be a big help tracking this down.

You're welcome. It looks like a very high tech genny. They keep changing like everything else. I would exercise it often too. It's probably not something you would want to start paying to have fixed. I have worked on whole house stand by units that self exercise every week for 15 to 20 minutes. AND that's with running on Nat gas or propane not todays funky gasoline.

[Alfred622]

To the OP... did you see the link to the service manual rjxj posted -

check Chapter 8 of that manual.

[jeffo]

On mine the faults are read by counting the flashes on the rocker switch. I am not reading any faults. My manual does mention an over cranking fault (if engine does not start after 30 seconds) but no mention of over priming. Tomorrow I will check the voltage to the fuel pump, it should be fused somewhere. Thanks for posting the link to the service manual. It should be a big help tracking this down.

[azrving]

OK. Huummm that was in the service manual and says hold the stop down for more than 3 seconds. I did notice a code for over prime which 30 seconds may do. The ecm goes into a protective state if it senses over prime. I dont know what the display is like but does it show any codes? If it has gone into over prime it may need to clear the fault. I didn't read enough to know if a certain amount of time passes it will clear on it's own.

[jeffo]

Yes, except my operator manual says to hold the rocker switch down for 30 seconds then up to start. When I hold the rocker switch in the down position to prime I normally hear the fuel pump running but now it does not seem to run.

[azrving]

Let me get a little more info. Did you do it this way? You probably did but I ran across this part so thought I'd check.



Press and hold
the stop switch for more than 3 seconds to cause the
fuel pump to prime the fuel system.


Startup:
Press and hold the start switch until the
genset starts. The controller:
1. Enables cranking.
2. Energizes the fuel pump E2 (gasoline models
only).
3. Depending on model:
A. Enables fuel injection
B. Energizes
the gasoline carburetor fuel
cut-
off solenoid E3 and choke heater
C. Energizes LPG fuel cutoff solenoid E3.
4. Flashes the field (F1-F2).
5. Flashes the status indicator light during crank-
ing.
6. Disconnects the starter when engine speed is
greater
than 1300 rpm and turns the status indi-
cator light on solid.
7. Turns on Switched B+ (remote pin J8-F).
8. Enables
output voltage two seconds after oper-
ating speed is reached.
9. Turns off field flash

[azrving]

jeffo wrote:
5.5 HGJAB. Not sure what the spec # is. I will try to find it tomorrow.

I'll look further. That may be enough

Service Manual

[jeffo]

5.5 HGJAB. Not sure what the spec # is. I will try to find it tomorrow.

[azrving]

With a quick look at the service manual it appears that it would start the pump. Need the model and spec number off your unit to actually look at a schematic and read their operation description as to what is doing what as you start it.