# Onan HGJBB won't start after parts replaced



## ErinR (Jul 10, 2020)

I recently changed the spark plug and fuel filter of my Onan HGJBB generator according to the maintenance schedule. I've had the process demonstrated for me before, but this was the first time I did it on my own. Prior to replacing the parts the generator started and ran normally. After replacing the spark plug and fuel filter the generator won't start up. It does run at a lower power while the start button is held down (after a 30 second prime), but immediately turns off after releasing the start button, then blinks a code 15. (From the manual: "Code 15 - Under Frequency: Indicates the engine governor is unable to maintain rated frequency. Reduce the number of connected appliances"). I honestly don't think it has anything to do with the load as the breaker switches are set to off when I start the generator anyway, and that nothing at all had changed except that the spark plug and fuel filter were replaced.

I don't know how to tell which part caused the change, though when I changed the fuel filter, I did have to pull a little on the fuel line to get it at an angle I could get at the clamps, so is it possible I pulled the line from the gas tank? I doubt it only because I didn't have to adjust it that far, but I'm throwing out that's what happened. (Yes, the fuel tank is full). It seems to be more possibly the spark plug? I can't be sure if I tightened it appropriately. I don't know if I need to tighten it further or is it possible to break if I tighten to much? This might be an easy fix, but since I'm new at it I appreciate any feedback of where I might have gone wrong. Thanks!


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## tabora (Sep 6, 2018)

If all you changed were the fuel filter and spark plug...

1. Put the old spark plug back in and try it. I have quality NGK spark plugs that still are going strong after 30 years. (Just clean them every few years.)
2. Verify that the new filter is oriented correctly. They are directional; there should be an arrow indicating flow. I usually change out the fuel lines along with the filter, too.


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## ErinR (Jul 10, 2020)

tabora said:


> If all you changed were the fuel filter and spark plug...
> 
> 1. Put the old spark plug back in and try it. I have quality NGK spark plugs that still are going strong after 30 years. (Just clean them every few years.)
> 2. Verify that the new filter is oriented correctly. They are directional; there should be an arrow indicating flow. I usually change out the fuel lines along with the filter, too.


Thank you for responding. So, yes I have the fuel filter in the correct direction. Per your suggestion, I cleaned off the old spark plug and put it back in. When I start up the same is happening that I described before though I now have a code 36 ("Code 36 - Engine Stopped: Indicates that the engine stopped without receiving a command from the control")


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## iowagold (Jan 22, 2020)

welcome to the forum!
question
did you have to "pull" on the fuel line?
you might look for tight bends or a pinched fuel line or hose.
also check the oil level to make sure you have plenty of engine oil.

from there we need to know the basics and some test gear is needed
click here for the test gear page
a inline spark tester would be nice. this will let you see visual the spark to see if the spark is the issue.
next a fuel pressure gauge to see if you have at least 1 lb fuel pressure just before the carburetor.
also look at the air filter to make sure it is clean..

this is the basic testing, fuel air spark...


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## Melson (Dec 8, 2019)

I'm going to assume this is a diesel engine? If so.....
My guess is air entered the fuel system when changing the filter.
You need to bleed the air out of the system- a somewhat messy procedure, but straightforward and not difficult. 
This should be explained in the owners manual; the best procedure can vary slightly depending upon the system. 
Basically, you crack open a fuel line or fuel fitting somewhere at a high point in the fuel system. Then crank the engine until fuel spits out from the opening. While still cranking tighten and/ or close that opening while fuel is being pushed out under pressure. 
This is how you purge air from the system. As mentioned, the exact procedure can vary slightly so is best to consult your manual. And, by the way, some systems can be exceptionally stubborn and take several attempts at this. 
If you cant figure it out any diesel shop or diesel repair shop could walk you through it.


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## Melson (Dec 8, 2019)

In my above post I said "crack open a fuel line..." I should have said "crack open a fuel injector line". That's because it's usually best to purge air at a point beyond the fuel injector pump. However, that being said, sometimes you need to purge air in multiple steps: First get all air out of the line feeding the fuel injector _pump_, and, then, if still no start, purge the air at the fuel injectors themselves.


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## ToolLover (Jan 13, 2020)

Hey Melson! You must have missed the part where she said she cleaned the spark plug.
You were correct about bleeding the diesel, but that spark plug is a tell tale.
I still liked your reply though.🆗


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## tabora (Sep 6, 2018)

The RV Onans (and many larger ones) automatically shut down if the charging circuit is not generating power (Code 27), and also if the low oil sensor is activated (Code 2) or if the auto-choke sticks in the open position when starting. Try disconnecting the low oil sensor first and see if it runs. If that doesn't do it, try holding the auto-choke lever at the top of the carburetor engaged while it runs for a while. Third, just try holding the start button on for up to 30 seconds even after the engine starts and see if it stays running. That overrides the charging circuit sensor. 

I have the older model of your unit (the KV Spec A MicroLite 2.8) and the basic troubleshooting is very similar, except yours has the electronic controls. Your Code 36 usually means low fuel level, so check your fuel pump flow. Pull the fuel line off at the carb and verify that you're getting a good fuel stream when the fuel pump is energized by the priming circuit.

Here's the electronic version of your manual: https://www.norwall.com/product_pdfs/3749_hgjbb_spec_a_b_om_2018.pdf


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## Melson (Dec 8, 2019)

@ToolLover ,...boy do I feel foolish. My dad would say 'it does ya good to eat a little humble pie'.


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## ErinR (Jul 10, 2020)

Hey guys, thank you all for the time you've put into giving me some suggestions and sharing your knowledge. Melson, sorry I didn't specify but it's actually a gas generator that has a fuel line feeding from the RV's gas tank. 

So I was hoping for an easy answer (isn't everyone?) given I only changed two parts and that I'm very much a beginner to learning about generators. All this information is very appreciated but some of these troubleshooting steps are out of my current skill level and available resources. I'm starting with what's most simple: Checked the oil level and it's showing a little above the max line (it was at max before so I'm guessing the increase of hot temperatures could make the oil expand??). The fuel line doesn't appear kinked or crimped from what is visible. I tried another startup and now it stays on for less than 10 seconds while holding down the start button, putters off, then again flashed fault code 15 as it did before. 

I do like to be self-reliant and learn how to maintain my own property, though I'm trying to weigh out my beginner skill level to the possible need to go to a shop that can help me. I'm a visual learner and can pick up on things quick when demonstrated to me in person or on a video with my same model of generator (I haven't yet found a YouTube video that can walk me through my exact problem on my exact model). 

Anyway, thank you again for all the feedback! Let me know if any of you know any more steps I could easily try as a beginner or maybe if you think it's worth taking to a shop. (And please don't be sending me seperate messages asking for my contact info, that's not what I'm on this forum for) Thanks!


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## iowagold (Jan 22, 2020)

make sure the fuel pump is working.
and that you have good fuel pressure... it should be 3psi to 5 psi..
if you had to pull on the fuel line it could to have kinked back in the chassis some where..
so inspect carefully.....

it has to be something simple...
hey is there a safety interlock switch on the cover of these units tab?
some of the real large gens have those...


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## iowagold (Jan 22, 2020)

hey try tripping out the output breaker and see if it runs!!
15 is an over loaded generator code...


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## tabora (Sep 6, 2018)

iowagold said:


> hey try tripping out the output breaker and see if it runs!! 15 is an over loaded generator code...


The OP stated in post 1 that she has the output breaker off...


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