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Old 10-19-2020, 06:01 PM   #1
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Onan 4K - Code 36 - Low Fuel or What?

Hello--

A concern with my Onan 4000 Microquiet series.

Background....

Purchase this TH last year. Genny ran fine when purchased. 145 hours on the clock. Brought it home and drained all gas out as owner said it was several months old. Serviced genny with new plug, new fuel filter, new air filter, and changed oil. All OEM Onan parts. Put in 5 gallons of fresh fuel. Genny ran but was running up/down in the rpms. I exercised it for one hour with AC running. I believe the RPM fluctuation was a dirty carb.

Now, 6 months later, I decided to run genny but went ahead and drained fuel as it was 6 months old. Put in 5 gallons of fresh fuel and added 2-3 ounces per gallon of Seafoam to clean carb and stabilize fuel.

Genny will not start. Primed for about 15 seconds and it wants to start but will not start. Removed fuel line at carb and pressed start to see if fuel was pumping and it was pumping fine.

Attempted to start again and this time primed for one minute and it started and ran for about 5 mins then stopped. The trouble code lights indicated 3 and 6 which is 36. In my Onan manual this code states low on fuel.

I went ahead an added 5 more gallons of fuel with more Seafoam (2-3 ounces per gallon). Primed a few more times and got it to start and ran for about 10 mins. RPM were running up and down, then settled, then went back to up/down. Went to turn on AC and genny died.

Questions:

1. Do TH gennys have the protective shut off of fuel when tank reaches 1/4 full... as do motorhomes? How would I know where/if this shut off valve exists on my TH?

2. Is it possible that 10 gallons (1/3 tank) is not enough fuel to run correctly?

3. What else can it be?

Thanks!
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Old 10-19-2020, 08:17 PM   #2
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Quote:
Originally Posted by SoCalAngler View Post
Hello--

A concern with my Onan 4000 Microquiet series.

Background....

Purchase this TH last year. Genny ran fine when purchased. 145 hours on the clock. Brought it home and drained all gas out as owner said it was several months old. Serviced genny with new plug, new fuel filter, new air filter, and changed oil. All OEM Onan parts. Put in 5 gallons of fresh fuel. Genny ran but was running up/down in the rpms. I exercised it for one hour with AC running. I believe the RPM fluctuation was a dirty carb.

Now, 6 months later, I decided to run genny but went ahead and drained fuel as it was 6 months old. Put in 5 gallons of fresh fuel and added 2-3 ounces per gallon of Seafoam to clean carb and stabilize fuel.

Genny will not start. Primed for about 15 seconds and it wants to start but will not start. Removed fuel line at carb and pressed start to see if fuel was pumping and it was pumping fine.

Attempted to start again and this time primed for one minute and it started and ran for about 5 mins then stopped. The trouble code lights indicated 3 and 6 which is 36. In my Onan manual this code states low on fuel.

I went ahead an added 5 more gallons of fuel with more Seafoam (2-3 ounces per gallon). Primed a few more times and got it to start and ran for about 10 mins. RPM were running up and down, then settled, then went back to up/down. Went to turn on AC and genny died.

Questions:

1. Do TH gennys have the protective shut off of fuel when tank reaches 1/4 full... as do motorhomes? How would I know where/if this shut off valve exists on my TH?

2. Is it possible that 10 gallons (1/3 tank) is not enough fuel to run correctly?

3. What else can it be?

Thanks!
Try replacing the carb. It only takes very little to make these carbs go bad.
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Old 10-22-2020, 02:39 AM   #3
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The first thing to do on that bad boy is to plumb in a fuel cutoff valve, then run the generator dry before you put it up for storage - a week or a year. The RPM hunting will be solved - but you still need to get the carb cleaned out. May I suggest Star Tron fuel treatment - It has worked well for my past carb issues.
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Old 10-23-2020, 11:13 AM   #4
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Since the Onan OEM fuel pumps and carbs are on national backorder, I'll start with replacing the pump with one from Amazon.

BTW...The Amazon carbs do have a fuel shut off, which is a pretty nice feature.
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Old 10-25-2020, 06:28 AM   #5
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Rather than replace, why not remove and clean? Takes a little time but a good cleaning might be all needed. You might need a rebuild kit which usually has the needle valves, gaskets, etc, BUT if you take apart carefully you might be able to reuse parts.
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Old 10-25-2020, 06:30 AM   #6
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Quote:
Originally Posted by SoCalAngler View Post
Hello--

A concern with my Onan 4000 Microquiet series.

Background....

Purchase this TH last year. Genny ran fine when purchased. 145 hours on the clock. Brought it home and drained all gas out as owner said it was several months old. Serviced genny with new plug, new fuel filter, new air filter, and changed oil. All OEM Onan parts. Put in 5 gallons of fresh fuel. Genny ran but was running up/down in the rpms. I exercised it for one hour with AC running. I believe the RPM fluctuation was a dirty carb.

Now, 6 months later, I decided to run genny but went ahead and drained fuel as it was 6 months old. Put in 5 gallons of fresh fuel and added 2-3 ounces per gallon of Seafoam to clean carb and stabilize fuel.

Genny will not start. Primed for about 15 seconds and it wants to start but will not start. Removed fuel line at carb and pressed start to see if fuel was pumping and it was pumping fine.

Attempted to start again and this time primed for one minute and it started and ran for about 5 mins then stopped. The trouble code lights indicated 3 and 6 which is 36. In my Onan manual this code states low on fuel.

I went ahead an added 5 more gallons of fuel with more Seafoam (2-3 ounces per gallon). Primed a few more times and got it to start and ran for about 10 mins. RPM were running up and down, then settled, then went back to up/down. Went to turn on AC and genny died.

Questions:

1. Do TH gennys have the protective shut off of fuel when tank reaches 1/4 full... as do motorhomes? How would I know where/if this shut off valve exists on my TH?


2. Is it possible that 10 gallons (1/3 tank) is not enough fuel to run correctly?

3. What else can it be?

Thanks!
Generally no. The 1/4 tank pickup on a motorhome is so you don't drain the tank and strand the motorhome. A trailer doesn't have that issue.
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Old 10-26-2020, 04:30 PM   #7
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Update.....

The genny is now able to run with some surging. I ran it for 2 hours and it smoothed out some but still has some surging. It was surging continuously before. I believe the Seafoam may have helped clean up the carb to some extent.

I checked pump at carb, and it does pump fuel.

NOW....As soon as I turn on the AC it begins to stall until it dies. As soon as I remove the load it runs again.

Thoughts?
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Old 10-28-2020, 08:41 AM   #8
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Quote:
Originally Posted by SoCalAngler View Post
Update.....

The genny is now able to run with some surging. I ran it for 2 hours and it smoothed out some but still has some surging. It was surging continuously before. I believe the Seafoam may have helped clean up the carb to some extent.

I checked pump at carb, and it does pump fuel.

NOW....As soon as I turn on the AC it begins to stall until it dies. As soon as I remove the load it runs again.

Thoughts?
I'll refer back to my previous reply post #5.
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Old 10-28-2020, 09:00 AM   #9
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The symptoms point to a sticking float valve. Seafoam, fresh gas, and time have helped, but the surging and lack of power indicate the generator is still running lean. The choice is either keep running it on low load hoping for improvement or have a mechanic drop the float bowl and clean the float valve and jets.
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Old 10-29-2020, 04:36 PM   #10
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There is no rebuild kit for this carb. It requires replacement. Service manual states replacement and does not mention any serviceable parts of carb.
I believe the bowl is removable but not sure how many parts are cleanable?

I purchase an Amazon China carb and will install this Saturday......As with most Chinese made things.....fingers crossed!

Once I remove OEM carb, I'll see what can be done in terms of cleaning bowl and jets. Perhaps I can do something to it and re-install if China carb does work properly.
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2003 Ford F-350 XLT, Super Duty - Crew Cab, 2WD, 6.5' Bed, SRW, 6.8L/V10, 3.73:1, 4R100. Level with cab topper and CargoGlide 1000 in truck bed
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Old 11-13-2020, 10:12 AM   #11
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Amazon carb appears to be no good. It runs at a fast idle and then shuts down as it is supposed to do (code 14).

I'll double check linkage and see if any errors in my install. I believe I installed just as it was with OEM carb.

NOTE: I tried the Amazon carb with the chance I would get a good one.......but as the saying goes....you get what you pay for!!

If I am unable to fix, I will have a new Onan carb installed.
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2003 Ford F-350 XLT, Super Duty - Crew Cab, 2WD, 6.5' Bed, SRW, 6.8L/V10, 3.73:1, 4R100. Level with cab topper and CargoGlide 1000 in truck bed
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