Hello, Writing to see if anyone has this issue and solution. My generator run great! When it runs. The problem I am having is it shuts down after about 1 hour of driving. It will shut down after about 3 hours of running while sitting.I had a tech look at it a while back and he told me I had air in the line. I replaced the lines, the fuel filters, and the fuel pump. Still having the problem.I am also wondering about the vacuum in my fuel tank. I have noticed when I take off the fuel cap that there is a lot of vacuum in the tank. This has me wondering if the amount of vacuum is to much for the fuel pump? The genset runs really good when driving until something changes. Like when I come to a stop or take a turn. That action has me thinking the vacuum is the problem as well. I am thinking that when the RV makes a turn or something, the vacuum increases a great deal due to the fuel being force to one side or another. Thoughts please...This is a strange one!Thanks,

If you have vacuum in the tank the vent system isn't working. While camped, remove the tank filler cap and see if the unit shuts down.

Freighguy, First off, may I ask what you've determined what "code 36" is? I've not heard of it. I, and many others on here who also own the 7.5QD model diesel gens have experienced the code "33" but, not a code 36. Code 33 on most is an "over heat" condition. And, the cause, or list of causes for the code 33 are several possibilities. But, I don't have my Onan trouble shooting book here in front of me to determine what a code 36 is. Now, it does sound like your fuel tank is not venting properly. If you are sure it's "vacuum" and not pressure, which, would be not good in either case, than some investigation into the cause of that is warranted. And, no, movement of the fuel in the tank causes no pressure/vacuum differences while driving. Besides, while driving your engine is using fuel too and, if you were experiencing a vacuum build up in the tank, I'd suspect that your engine would eventually shut down too due to the transfer pump not being able to over come the vacuum. But this is all speculation. So, if your hoses are good, and your fuel pump on the gen is good, and the filter is good, the first thing I'd maybe have a look at is the fuel tank on the rig to make sure the venting system is working properly.Scott

The manual says:ENGINE STOPPED FAULT—CODE NO. 36 (Engine stopped without command by controller) Corrective Action:1. Check fuel level. (Note: The genset fuel pickup is probably higher than the vehicle engine pickup.)2. Prime the engine fuel system by holding the control switch down in its Stop position for at least 1 minute.3. Check the engine air filter and remove any blockage.4. Check for mechanical damage.By doing google searches I have many people with this problem and code. Seem to be a general code to cover several potential issues.

I have seen the fault code 36 a couple of times due to a low fuel level below ¼. The generator was not running at the time of the low fuel but after filling the tank the generator stuttered and died the next time I tried to start it. Holding the prime/stop switch down for a minute cleared the problem after a couple of 1 minute primes.

You need to vent the fuel tank. It's a wonder the main engine doesn't stall too.

Onan 7500 HDKA getting code 36 | Good Sam Community

Freightguy
Explorer
Jun 11, 2013
RedG wrote:
Freightguy wrote:
***UPDATE***
I when on a 2 hours trip and I loosed my fuel caps to allow venting. I figured that if my problem is the fuel tank vent then the generator would run fine. It did run longer than normal but then it quit and threw out code 14. Then when the weekend was over we got on the road again and did the same thing but this time it threw out code 13 when it quit. So now I have seen codes, 35, 36, 14 & 13. All these codes refer back to the control board. So I am thinking control board. Any thoughts.

My thoughts are that you're probably smarter than most of the responders and will get this resolved on your own.......

I think I like you!
RedG
Explorer
Jun 11, 2013
Freightguy wrote:
***UPDATE***
I when on a 2 hours trip and I loosed my fuel caps to allow venting. I figured that if my problem is the fuel tank vent then the generator would run fine. It did run longer than normal but then it quit and threw out code 14. Then when the weekend was over we got on the road again and did the same thing but this time it threw out code 13 when it quit. So now I have seen codes, 35, 36, 14 & 13. All these codes refer back to the control board. So I am thinking control board. Any thoughts.

My thoughts are that you're probably smarter than most of the responders and will get this resolved on your own.......
Freightguy
Explorer
Jun 11, 2013
***UPDATE***
I when on a 2 hours trip and I loosed my fuel caps to allow venting. I figured that if my problem is the fuel tank vent then the generator would run fine. It did run longer than normal but then it quit and threw out code 14. Then when the weekend was over we got on the road again and did the same thing but this time it threw out code 13 when it quit. So now I have seen codes, 35, 36, 14 & 13. All these codes refer back to the control board. So I am thinking control board. Any thoughts.
Freightguy
Explorer
May 31, 2013
Fritz, as I mentioned before I change the filter you are referring to each time I do my oil change. However, there is another "in line" filter located on the feed line from the tank about 2 feet before the line goes into the generator. I change both of these with each oil change. Also, as I mentioned before I have also replaced the fuel lines from the tank to the genset and the fuel pump.
PFGuil49
Explorer
May 31, 2013
Freightguy,
You should have only one fuel filter on your Onan 7500. This is a separate filter from the 2 fuel filters for the main diesel engine. When you open the access door under the generator, the fuel filter will be secured against the front wall. It is square and looks like a mini oil cooler with a smooth surface. It should have 2 stainless lines (1 inlet and 1 outlet) with a nut in the center of the filter to secure it. My buddy had the same problem you're having with the 36 code. It turned out to be what Tntman described above.

Fitz
Freightguy
Explorer
May 30, 2013
Tntman wrote:
My Onan coded 36. went to Cummins/Onan, Houston Tx. 36 in my case was a clogged fuel filter inside the gen-set. These folks fixed the fuel filter problem, changed my oil and filter and charged me a little over $400.
You can change the fuel filter yourself with patience and getting into tight places. There is a steel fuel line that the mechanic? broke another $28. The steel line must be loosened to remove the old fuel filter.

Thanks, but I have already replace the lines from the tank and I change both filters each time I change the oil. I have also replaced the fuel pump. I am really leaning toward to much vacuum in the tank right. Probably due to a clogged tank vent. Next time I take a trip I am going to run with the fuel cap loose and see what happens.
Tntman
Explorer
May 30, 2013
My Onan coded 36. went to Cummins/Onan, Houston Tx. 36 in my case was a clogged fuel filter inside the gen-set. These folks fixed the fuel filter problem, changed my oil and filter and charged me a little over $400.
You can change the fuel filter yourself with patience and getting into tight places. There is a steel fuel line that the mechanic? broke another $28. The steel line must be loosened to remove the old fuel filter.
wilpower
Explorer
May 29, 2013
Freightguy wrote:
So are the fuel caps supposed to be doing the venting?

No, there should be a vent line on top of the fuel tank. It may be kinked or clogged.
Freightguy
Explorer
May 29, 2013
So are the fuel caps supposed to be doing the venting?
dkreuzen
Explorer
May 29, 2013
You need to vent the fuel tank. It's a wonder the main engine doesn't stall too.

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Onan 7500 HDKA getting code 36

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