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Old 05-23-2021, 11:32 PM   #29
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ONE of biggest problems for Gas or Diesel is the LOW PRESSURE FUEL PUMP Because THE LITTLE SLIDING Piston pump fools you by being INTERMITTENT, and when first failing, maybe not until 90-120-minutes run...(often with a variety or other symptoms such as SURGING) many owners with (some brands of RV) blame OVERHEAT/ VAPOR LOCK, which (may/may not) be an influence on (some) but not all, but it is currently a $30+/- part in (most cases) or OEM= $100+/-?. MY suspicion after disassembing my 20yo/ 200-hour pump was fuel contamination, (had white putty like substance on piston & bore wall, that I NOW suspect (right/wrong?) is maybe TEFLON dope pipe sealant from station fuel tank/ hose fitting/ piping?) Diesel LP pump gets fuel to HIGH Pressure pump for Injectors; not much read// found on problems w/ diesel HP pump? BUT LP pump similar/ same on gas and diesel, with similar failures? and ONAN TEST is "greater than x-PSI", which Most owners cannot do, (NOT "pulled line loose and it flowed fuel" as many onwer/ troubleshooters do), so easier/ cheaper and FASTER to change pump. and new pumps seem to have low fail rate? (Have read of one new fail, but... ?) I do KNOW Diesel HARD to stop if it is getting fuel and shutoff METHOD is always STOP FUEL FLOW, and Code 36 says "controls did NOT shut off engine"? LUCK
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Old 05-23-2021, 11:35 PM   #30
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p.s tale/ TIP: When I first bought Rv TS/ BRAKE Light problem, checked fuses x3 times and then spent a week chasing wires, only to recheck and FIND blown fuse that I had checked x3 times... so ROKETENGINER, are U getting my drift? Yeah, I know I am getting old, and used to be better in my youth.. :-)
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Old 05-24-2021, 03:36 PM   #31
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Originally Posted by THenne1713 View Post
p.s tale/ TIP: When I first bought Rv TS/ BRAKE Light problem, checked fuses x3 times and then spent a week chasing wires, only to recheck and FIND blown fuse that I had checked x3 times... so ROKETENGINER, are U getting my drift? Yeah, I know I am getting old, and used to be better in my youth.. :-)
I don't mean to be rude, but no I don't understand what you are getting at.

Are you saying vaporlock is the majority cause of these things?

Or the lift pump getting too hot?

Or there being FOD in the diesel fuel?
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Old 05-24-2021, 10:48 PM   #32
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OK, so (you said) you had "checked" A, B, C ... (including fuel pump) and (I said) "only to recheck and FIND blown fuse that I had checked x3 times... a week earlier" BET YOU did not check fuel pump PRESSURE? BUT (I would) spend $30 and replace FP anyway... suspect that diesel board is NOT just $30? (Believe someone said $1500 recently, but maybe wrong) and yeah, board may have a RELAY that is intermittent that controls FPUMP, but start w/ cheap items FIRST? Hope this helps? p.s. Oh, and I guess it doesn't matter WHY, if old worked for a period, and a new one will make the problem go away?
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Old 05-25-2021, 06:18 AM   #33
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Crazy question, but have you disconnected power to the generator underneath for 30 mins and wire brushed any corrosion from the cable terminal ends and mounting studs? I had an issue recently with my 7500QD and this actually fixed my issue. An aviation mechanic suggested this to me as he said this is how they clear codes on planes.
Similar situation when I was getting a 36 code on my 10hdkca I was going bonkers trying to figure it out. To net out a very long story, it was the power cable from the chassis batteries that runs for some 40+ ft to the genset. It was failing internally and would result in shutting down the electric fuel pump throwing the 36 code.
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Old 05-25-2021, 06:41 AM   #34
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If you do end up replacing the board make sure you call Flight Systems first. Their replacement boards are a fraction of the price of Cummins.

https://www.flightsystems.com/standb...-controls.html
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Old 05-25-2021, 09:43 AM   #35
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OK, so (you said) you had "checked" A, B, C ... (including fuel pump) and (I said) "only to recheck and FIND blown fuse that I had checked x3 times... a week earlier" BET YOU did not check fuel pump PRESSURE? BUT (I would) spend $30 and replace FP anyway... suspect that diesel board is NOT just $30? (Believe someone said $1500 recently, but maybe wrong) and yeah, board may have a RELAY that is intermittent that controls FPUMP, but start w/ cheap items FIRST? Hope this helps? p.s. Oh, and I guess it doesn't matter WHY, if old worked for a period, and a new one will make the problem go away?
Gotcha! Yeah they are around $600-$900, not cheap.

Right now I've ordered some relays to replace the K1, K2, K3 relays. I'm going to check for proper voltage at the generator, then I'm going to straight up wire the fuel pump to a relay and if it runs longer than 15 hrs I know its the PCB controller.

I had to wire my old onan like that (7kw; 1993 model marquis) to the hobbs meter with a relay to turn on the fuel pump.... NEVER had an issue after that. It had ~6,000 hours on it when I sold the old Bounder.
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Old 05-25-2021, 12:53 PM   #36
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Originally Posted by THenne1713 View Post
OK, so (you said) you had "checked" A, B, C ... (including fuel pump) and (I said) "only to recheck and FIND blown fuse that I had checked x3 times... a week earlier" BET YOU did not check fuel pump PRESSURE? BUT (I would) spend $30 and replace FP anyway... suspect that diesel board is NOT just $30? (Believe someone said $1500 recently, but maybe wrong) and yeah, board may have a RELAY that is intermittent that controls FPUMP, but start w/ cheap items FIRST? Hope this helps? p.s. Oh, and I guess it doesn't matter WHY, if old worked for a period, and a new one will make the problem go away?
He replaced the fuel pump in post #22.
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Old 05-26-2021, 08:01 PM   #37
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Ok, everyone. I'll close this thread out here.

I replaced the K1, K2, K3 relays with some SPDT relays. Didn't solve my problem of my fuel pump NOT priming when I try to prime it. So now I'm about 99% sure the problem is in the computer/PCB/controller.

THIS is what I did.

Using the schematic in the service manual for the HDKCA I found a 12v power source off the 'Status Indicator' LED. This light will illuminate when 1) priming 2) when generator is running 3) when starting. I tapped off that line and Tee'd a wire into it that I ran to the (+) side of the fuel pump. I soldered it and used a wire that can handle 15a of current. I also verified the wire wasn't overheating with my infrared camera.

So far this new set up has been running ~2.5 hours with the a/c's and other components pulling ~45amps. Which is more than a half load. No overheating, no surging, EGT: ~300F, Coolant: ~165F, Oil PSI: ~44PSI. I've also noticed that there's less vibration (maybe because I put in alot of seafoam and its been cleaning the injectors?). Overall, Kubota engines are bulletproof as I've always known.

My assumption is this. The 36 code is when the generator drops below 1000rpm for more than .5 seconds. My guess is the generator would run fine on a light load WITHOUT the lift pump working (because the computer told it to stop?), but as soon as the a/c compressor/coffee maker/etc. clicked on the amp draw was enough to lug the generator down, making it unable to keep up with less than optimal fuel draw and the engine would plum quit.

I can 100% say that the computer is bad and I'm going to be ordering the flight systems one here shortly. It sucks something so expensive has to go bad, but this is RVing.

In conclusion, simple & cheap first, find a service manual, common sense. And ask questions; can't forget that.

Y'all have a good one!
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