gmac Posted May 23, 2009 Share Posted May 23, 2009 Greetings. i have an 84 new horizon with built in onan generator. Ran 20 - 30 minutes today while i ran the ac, then shut off and wouldnt start back up (the gas tank was full too ruling out the generator shutting off when the fuel tank gets to half). I left it running in the driveway to make sure it would run while driving down the road. Can anyone help? gmac Quote Link to comment Share on other sites More sharing options...
WME Posted May 23, 2009 Share Posted May 23, 2009 Check to see if there is fuel in the carb. Also try removing the gas cap and see what happens. Maybe the Onan pump is to weak to pull against the vacuum in the tank after the Onan has been running for awhile Quote Link to comment Share on other sites More sharing options...
Maineah Posted May 23, 2009 Share Posted May 23, 2009 The air filter assembly leaves a bit to be desired mine twice has worked loose and the air filter blocked the carb intake and flooded it, might check that. Have a look at the two fuses too. Quote Link to comment Share on other sites More sharing options...
Bodybagger Posted May 24, 2009 Share Posted May 24, 2009 First, was the AC running when you shut off the generator under load? If so, you may have a bridge rectifier failure. Otherwise... Your oil pressure switch is probably indicating a low oil pressure condition and it automatically will shut off. When starting it, hold the start switch in until well after it starts, say 5-10 seconds. If it runs until you let go of the switch and immediately cuts off, this confirms the diagnosis. One of the problems I have run into is that Mobil 1 will foam in these units and cause the oil pump to lose its prime. This switch prevents catastrophic engine failure in that even. Once it has foamed really good, it takes forever to re-prime. If it will start and run until you release the switch, try this simple fix. Change your oil and filter and use a conventional SAE 30 oil. That will boost your oil pressure and can overcome a weak oil pressure switch. If the problem persists, you'll need to remove the oil pressure switch and test its operation (it should trasition from closed circuit to open circuit around 3-8 psi). See http://users.california.com/~eagle/generator.html#switch Now if you genuinely have low oil pressure, you need mechanical service on your generator or you will burn up the engine. Quote Link to comment Share on other sites More sharing options...
Maineah Posted May 31, 2009 Share Posted May 31, 2009 http://www.gmcws.org/Tech/dsimmons/onan/on...#general-repair Good repair procedures and wiring. Quote Link to comment Share on other sites More sharing options...
gmac Posted June 1, 2009 Author Share Posted June 1, 2009 Thanks for the info. The ac was running when it shut off (however I didnt shut it off). Since the day I posted this, I have only been able to start the generator once for about 5 minutes, otherwise havent been able to get it started. I detached the fuel line and hit the start button, fuel pump didnt pull anything, was thinking I might need a new fuel pump and it was going out slowly..........?? What is bridge rectifier failure? How is it repaired? Thanks gmac http://users.california.com/~eagle/generator.html#switchNow if you genuinely have low oil pressure, you need mechanical service on your generator or you will burn up the engine. Quote Link to comment Share on other sites More sharing options...
Bodybagger Posted June 13, 2009 Share Posted June 13, 2009 What is bridge rectifier failure? How is it repaired? A bridge rectifier is 4 diodes arranged into one unit that takes AC voltage on 2 legs and outputs DC voltage on the other 2 legs. Diodes have a peak inverse voltage that they can withstand before breaking down. Shutting down the generator under load causes voltage spikes that can exceed the limitations of the originals. Without the bridge rectifier, your genset cannot maintain the feedback loop of converting the generator's AC into DC to feed into the rotor to regulate the voltage. Some models of control boards will shut down the generator if it is not making 120 volts. Some models of Onans have a bridge rectifier that is part of the voltage regulator circuit. Some have this bridge rectifier buried in an epoxied modular voltage regulator. Some will run without the VR and some will not run at all without the VR. Depends on the model. On some where you can get to the bridge rectifier, you can replace it with a 5 dollar one from radioshack. On the ones with the modular voltage regulator, you'll have to order an aftermarket one from Flight Systems for $200 or from a Cummins/Onan dealer for $389. Of course all this depends on what model of Onan you have. Troubleshooting these in person can be a pain. If it's not something obvious, you'll be troubleshooting electronics. Quote Link to comment Share on other sites More sharing options...
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