Onan Diesel QD7500 won't run

[ladagobago]

Onan QD7500 Diesel been run about every month and now throws code not sure if it is 11. or 2
Fuel delivery ok 500CC in 60 seconds, Oil and Cooling OK. Primes and then pulls solenoid and Starts for about 2 seconds and stops. Tried running the fuel pump with constant 12 volt but made no difference. Check fuses all OK. Still trying to figure out how to pull the two harness plugs to he control board. …. Any ideas as to the problem would help.

[gerdutch]

Not sure if its your problem, but read an OP two weeks ago ref that Unit having Fuel injector pump problems. Sure enough i began my trip out west and mine started acting up, shutting down. run time became shorter and shorter. Found the Fuel pump in San Antonio. Picked it up and had friendly mechanic BeBe install it in Van Horn texas in an hour and half at the RV park.

Cured my problem.
Your problem sounds like it may be the fuel filter of which you may have an exsternal ine filter and the internal next to the pump. You didnt mention how many hours on the Genny and last time it was serviced.

[OCM]

Oil level?

[flyboy013]

I couldn’t find an 11 fault code in the service manual, but I did find a 2.

[ladagobago]

a

Originally Posted by gerdutch

Not sure if its your problem, but read an OP two weeks ago ref that Unit having Fuel injector pump problems. Sure enough i began my trip out west and mine started acting up, shutting down. run time became shorter and shorter. Found the Fuel pump in San Antonio. Picked it up and had friendly mechanic BeBe install it in Van Horn texas in an hour and half at the RV park.

Cured my problem.
Your problem sounds like it may be the fuel filter of which you may have an exsternal ine filter and the internal next to the pump. You didnt mention how many hours on the Genny and last time it was serviced.

There are two pumps. one is the lift and the other is mechanical injector pump. I wrote that mine has a 500 cc delivery in one minute which is twice that required. Which pump did you replace and how much was it.

[ladagobago]

Originally Posted by OCM

Oil level?

I believe I wrote that oil and water OK.

[ladagobago]

Originally Posted by flyboy013

I couldn’t find an 11 fault code in the service manual, but I did find a 2.

Attachment 328817

Thanks I saw that and want to bypass the switch but have to remove the connector to measure the resistance to that sensor. Sensor is not accesable with out removal of generator from the rear frame. This is not on a slide.

[153stars]

Both codes would allow genny to start and have delay and cause shut down . The bad pressure switch or connection I'm sure is more common.
Flight Systems have a very good troubleshooting flow chart as well as other good info.

[Mile Marker 42]

So I had a similar problem with my 7500 QD but I think the code was 25. All fluids and filters were fine. We don't use our generator except to exercise. It only has 750+ hours on it. My issue is that it always took 3 tries to start it. The first 2 it would run for a second and then shut off. The 3rd time it would start and stay running. Then, one day I went to exercise it and it ran for 10 mins and shut down. It did this 4 more tries. I posted on this site about my problem and asked if anyone had any magic tricks to clear the code on my generator. A airline mechanic said I should try to disconnect power from the generator underneath and wire brush the corrosion off the mounting studs and cable ends. He suggested I leave everything unhooked for half an hour and then rehookup. Then he suggested I hold down the start button at the generator for 60 seconds and try starting. Believe it or not, this fixed my issue. Might be worth a try on yours.

[ladagobago]

Originally Posted by Mile Marker 42

So I had a similar problem with my 7500 QD but I think the code was 25. All fluids and filters were fine. We don't use our generator except to exercise. It only has 750+ hours on it. My issue is that it always took 3 tries to start it. The first 2 it would run for a second and then shut off. The 3rd time it would start and stay running. Then, one day I went to exercise it and it ran for 10 mins and shut down. It did this 4 more tries. I posted on this site about my problem and asked if anyone had any magic tricks to clear the code on my generator. A airline mechanic said I should try to disconnect power from the generator underneath and wire brush the corrosion off the mounting studs and cable ends. He suggested I leave everything unhooked for half an hour and then rehookup. Then he suggested I hold down the start button at the generator for 60 seconds and try starting. Believe it or not, this fixed my issue. Might be worth a try on yours.

Shunting of the on board ckt breaker isolates the output from the chassis. when the engine starts, the computer flashes the system and shuts off the starter and solenoid at startup so it is not possible to hold the start switch down after it starts. In fact to restart you have to release the start switch.. I have hooked up a separate battery to power the lift pump since the DC ckt also shuts off the power to the fuel pump after 2 seconds. Even with the fuel pump on continuously the engin still shut down. The battery bank is fresh with four 6 volt deep cycle golf cart batteries so there a huge supply to crank this little motor.

[ladagobago]

Originally Posted by 153stars

Both codes would allow genny to start and have delay and cause shut down . The bad pressure switch or connection I'm sure is more common.
Flight Systems have a very good troubleshooting flow chart as well as other good info.

that is why I need to get to the two plugs. can not get to the the pressure switch with the genny in the RV. it is in the back and the procedure to get to it requires removal of the back cover, muffler system and other items.

has anyone ever removed the two connectors to the computer.????

[Mile Marker 42]

Originally Posted by ladagobago

Shunting of the on board ckt breaker isolates the output from the chassis. when the engine starts, the computer flashes the system and shuts off the starter and solenoid at startup so it is not possible to hold the start switch down after it starts. In fact to restart you have to release the start switch.. I have hooked up a separate battery to power the lift pump since the DC ckt also shuts off the power to the fuel pump after 2 seconds. Even with the fuel pump on continuously the engin still shut down. The battery bank is fresh with four 6 volt deep cycle golf cart batteries so there a huge supply to crank this little motor.

Not sure if you understood my posting, but appears you mistook what I wrote because I didn't say anything about holding down the button after restart . Might try reading it again, it might help you, but no guarantee.

[ladagobago]

Originally Posted by Mile Marker 42

Not sure if you understood my posting, but appears you mistook what I wrote because I didn't say anything about holding down the button after restart . Might try reading it again, it might help you, but no guarantee.

Guess I don't understand--- " Then he suggested I hold down the start button at the generator for 60 seconds and try starting". When I push the start button the engine starts for 2 seconds and stops. At that time the computer drops the starter and pump power so maintaining pressure on the switch for any additional time has no effect. I also tried holding it in the prime position for 60 seconds with no result in the start sequence.

[Mile Marker 42]

Originally Posted by ladagobago

Guess I don't understand--- " Then he suggested I hold down the start button at the generator for 60 seconds and try starting". When I push the start button the engine starts for 2 seconds and stops. At that time the computer drops the starter and pump power so maintaining pressure on the switch for any additional time has no effect. I also tried holding it in the prime position for 60 seconds with no result in the start sequence.

Holding down (not up)the start button for 60 seconds, and then trying to start the generator, was after you have disconnected the power to the generator underneath for 30 mins and wire brushed the terminal ends and terminal stud mounts. As I said, this was my fix. Not sure if it will help you, but may be worth a try.