Onan generator 7500

[Randy Keaveny]

I noticed no lights or display on the genset while trying to start.   The pre heat button on the unit itself use to light up prior to starting.   I thought.    Anyone

Randy

[Eric Maclean]

Randy
Does the unit start normally or is it hard to start in cooler weather?

[Randy Keaveny]

Right now it won't start at all. I'm going to change fuel filter and see if that helps.  But. I'm at a loss right now.

[Eric Maclean]

Randy
 does it crank over and not start or does it not do anything?
When you push the switch to the prime position do you hear the fuel pump run?

[Eric Maclean]

Randy
At the gen set if you push the switch to prime you should hear the electrical fuel pump ticking as it pumps fuel through the fuel system.
When you push and hold the switch to the start position the light in the switch should flash on and off while the unit is preheating the glow plugs this will take longer in cold weather , once the glow plugs have preheated then the engine will crank and once the engine has started the light should come on solid and stay on until you shut it down.

Randy under the small cover above the switch on the gen set there should be three fuses if the light does not light up the F1 fuse may be blown.
If F2 is blown the glow plugs won't work and the gen set will be hard to start.
And if F3 is blown the starter will not function.
In the coach assist section of the forum there is a service manual for the Onan 7500 quiet diesel generator on page 70 and or 71 you should find the troubleshooting for your problem.

Fuses
F1= control power b+.   15 amp
F2= starter power           15 amp
F3= glow plugs power.   25 amp

Keep us apprized of your progress
Eric

[Randy Keaveny]

So fuses all good.  Coolant full. Oil full.  But. Still cranks  no start.  Fuel level is now just under half.  Just seems strange that I burned that much fuel just sitting here.  Running engine couple times. Heater Fir a few days.  And genset just to exercise.
I do now have a red light on switch Fir pre heat and start.  It's just flashing really fast.  Guess I'll try to change fuel filter. See if that helps


Thanks
Randy

[Eric Maclean]

Randy
The fast flashing light in the switch might be a fault code if there are breaks in the flashes creating a pattern.
Read the troubleshooting section in the Onan service manual to understand how to retrieve fault codes and go from there.

If all the fuses are good and the light flashes for several seconds before the engine cranks the controller is working as designed
The problem would be either glow plug operation or more than likely fuel related .
As for fuel filter being plugged the gen set runs from the same tank as the engine usually if you have a fuel problem ( dirt or water) the first filters to pick it up is the vehicle engine filters as that engine moves a whole lot more fuel than the gen set and picks its fuel up lower in tbe tank.

First thing to do is remove the fuel return line from the back of the set and run the priming pump to see if you get fuel returning to the tank if no fuel try a fuel container connected to the feed line to eliminate the fuel suction line and or tank
Pickup as the problem .

[Randy Keaveny]

Ok. Got it running with bleeding and new fuel filter. But only ran for about 3 minutes tops.  Then died.  Flashing 3 times.  That's all I can get out of it.   3 flashes.

[Eric Maclean]

Randy
According to the troubleshooting the 3 flashes indicate a second level fault and by pushing the switch in the stop position the system should then flash a fault code which you can troubleshoot from.

[Randy Keaveny]

Ya I can't get it to do it again.  20 degrees out. So. I'll try again tomorrow. See if there's bubbles in the return line again.    Thought I had her when I changed filter and she fired right up.

[David T. Richelderfer]

Sounds like the diesel has waxed up the fuel filter.  You filled the tank with a winter blend of diesel or used a winter additive?

[Randy Keaveny]

I did not. But.  Just added 50 gals of fresh fuel. It acts like it  loses prime but has plenty of fuel.   Engine starts.  Heater is working.   I'll prob bleed again tomorrow.  See what happens

[Eric Maclean]

Randy
If you are experiencing fuel waxing you could try heating the warming the fuel filter with a heat gun or hair dryer and running the priming pump to get fuel to move through the injector pump it may take several tries to get fresh fuel through tge system

You could also run the coach engine in an attempt to raise the temperature of the fuel in the tank but with 100 gallons of fuel in that tank it would take all day with the engine running ( probably only feasible if your on the road ).

A good fuel conditioner would help as well.

It may also be losing prime by sucking air through a bad supply hose may still be worth trying to run it from a fuel container with warm fuel rather than the tank supply line.

[David T. Richelderfer]

If you did not "winterize" your diesel fuel, then almost certainly at 20F it will start solidifying by forming small wax particles.  The wax particles will plug the fuel filter after a few minutes of the engine running.  If the fuel in your coach's tank has a high percentage of bio, say 10% or higher, then waxing can occur at temperatures of 35F, perhaps even at higher temperatures if the bio percentage approaches 20%.

In addition to other suggestions, you could also try placing a heat lamp, or several of them, under the engine, fuel lines, and tank to warm them up to encourage the wax particles to "melt" and reconstitute back into the fuel solution.  Once warmed up, change the fuel filter again, and try to start the engine.  And as soon as possible, winterize the fuel system by using an additive or adding #1 diesel (stove oil) to the tank and run it through the system (through the lines, filters, and into the engine) before shutting down the engine.