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Old 01-13-2022, 05:09 AM   #1
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Onan 7500 cranks for 5 seconds only

Hi everyone, I am a new owner of a 2000 alpine coach and a first time class A owner. I purchased this RV with a few known issues I will just address my main one at the moment and that is my generator. So here is all I have done to try to get it to run.

I am getting fault code 32 which is slow crank under 180 rpms I believe, however it sounds like its cranking normal. When I start the motorhome engine it does crank a little faster but not by much. I have checked my voltage at the house batteries and at the generator and both are reading 12.6v. I even put a jump pack on the generator itself and I'm still only getting the cranking for 5 seconds then it shuts down. so no matter how many times or how long I hold the start button it will only crank for 5 seconds and then turn off. I checked the 3 fuses and they are all good. I then cleaned all the terminals both on the battery side and the generator side including the ground for the generator and still same issue. I also flow tested the fuel pump using the return line on the back of the generator and I'm getting about half of a water bottle of fuel in a one minute time frame. i replaced the air filter with a new one and tried to do an oil change but the drain bolt acts as if its welded on that's how tight it is on there. i also ordered a new fuel filter but that wont get here for about a week. I should mention that this coach sat from 2005 and i think the previous owner did some maintenance on it back in 2018 however that was just tires and brakes. What i am suspect of is the injection pump. the reason is when I crack the fuel line at the injection pump coming off the fuel filter its getting fuel when i crank, however when I crack the injector no fuel is coming out at all. I'm not to familiar with the injectors but there are 3 nuts on them i believe one for the high pressure line, the next one for the return line and the last one is the injector itself I believe, someone correct me if I'm wrong. well the reason i bring it up is because when i take off the high pressure line off the injector and then loosen the nut that follows for the fuel return line and then crank the engine i can see fuel coming out of there. I really don't want to take this thing to the shop if i can fix it myself. any help would be greatly appreciated. thank you
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Old 01-13-2022, 10:10 AM   #2
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Have you load test the batteries? voltage doesn't mean that there is amperage needed to actually crank.
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Old 01-13-2022, 10:16 AM   #3
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No but they are new and I jumped the generator directly at the generator and later tried having the coach engine on with same results
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Old 01-13-2022, 10:46 AM   #4
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No but they are new and I jumped the generator directly at the generator and later tried having the coach engine on with same results
A fairly common issue with our Onan gensets is corrosion of the rear 12v battery connections--inside/outside the cabinet. Even if you jumped the genset at these terminals--you may have compromised connections. You may see 12+ volts but not be getting sufficient amp draw to properly crank the engine.
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Old 01-13-2022, 12:06 PM   #5
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No but they are new and I jumped the generator directly at the generator and later tried having the coach engine on with same results
Good, just wanted to make sure you weren't trying to use the old batteries.
Also as Old scout said along the same lines, I found a connection on the back of the gen that was lose on mine.
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Old 01-13-2022, 02:11 PM   #6
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Has anyone considered that the rpm sense on the generator could be defective?
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Old 01-13-2022, 03:16 PM   #7
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i was not aware that they even had an rpm sensor
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Old 01-13-2022, 03:44 PM   #8
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A fairly common issue with our Onan gensets is corrosion of the rear 12v battery connections--inside/outside the cabinet. Even if you jumped the genset at these terminals--you may have compromised connections. You may see 12+ volts but not be getting sufficient amp draw to properly crank the engine.
This is a commonly overlooked but fairly popular issue with this generator. I would disconnect those cables completely and wire brush the cable ends and stud mounts. If it doesn't fix your issue, at lest you have knocked this off your maintenance list. Here is the diagnostic:

LOW CRANKING SPEED FAULTóCODE NO. 32
(Cranking speed less than 180 rpm for more than 2 seconds)
Corrective Action:
1. Replace Fuse F2 (starter solenoid) if blown (Page 7).
2. Clean and tighten the positive (+) and negative (Ė) battery cable connections at the battery and at
the genset (Page 17).
3. Recharge or replace the battery. Refer to the battery manufacturerís recommendations.
4. Replace the engine oil with oil of proper viscosity for the ambient temperature (Page 16). (High oil
viscosity can slow cranking speed.)

I'd be checking your voltages at the terminals of the generator.
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Old 01-13-2022, 05:17 PM   #9
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PS--corrosion on rear 12v posts can be on the cables inside the cabinet too--so cleaning only the outside cable connections may not solve the problem.
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Old 01-14-2022, 01:43 PM   #10
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Well I want to update you guys, I went back and re cleaned all the terminals and I also took apart the injection pump and the injectors and cleaned everything. Put it all back and the generator was finally showing that It wants to start and I even was getting smoke from the exhaust. Well that excitement didn't last. After trying to start it a few times the rotor felt like it was getting harder and harder to spin. I then noticed It was missing a few pieces of magnet so I'm suspicious that thats what Is why I'm having a hard time. At this point I want to figure out how to get the side cover off without removing the generator from the slide.
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Old 01-14-2022, 10:24 PM   #11
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Well here is what I found so far
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Old 01-14-2022, 10:26 PM   #12
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Well I found out that 3 of the magnets came loose and were just being dragged by the engine when I would try and start it. I wanted to know if this could cause a start and then almost and instant stop when trying to start the engine?
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Old 01-14-2022, 11:34 PM   #13
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Well I found out that 3 of the magnets came loose and were just being dragged by the engine when I would try and start it. I wanted to know if this could cause a start and then almost and instant stop when trying to start the engine?
I own a 7500QD but am not a magnet expert. I would think it would start with broken magnets unless the broken pieces spun off and damaged something or wedged themselves and are keeping the engine from spinning over. Can you turn the engine over by hand? Search this site as there are many posts related to your issue. You should fully open the generator and see what is going on.
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Old 01-15-2022, 12:20 AM   #14
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The generator starts without a problem now that I took the rotor off, however it dies almost instantly
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