Onan Generator Wont Start in the SNOW! 

Electric fuel pumps are designed to "push" the fuel from the tank to the engine. Relocating the pump to the tank area would greatly improve the pumps performance.

There is another fuel filter in the system. It is in the feed line to the pump, under the bleed screw. take the big nut out and there is a screen under neath.

I've some experience with onan gen sets in the RV industry. Typically the fuel supply intake for the gen set within the main tank is positioned so you can't run the tank dry with the generator. The fuel level in the tank has to be above 25% or so. It seemed like you had a solid fuel supply although there was some air. Thanks for the videos!:) I always learn something new!

Back in the Cat PC truck engine days. You would put a AMP meter on the glow plug harness and measure AMP draw to see if all glow plugs was working properly. If I recall a good system would pull around 60 AMPs on a 12 volt system, 6 cylinder engine. Also had a series parallel switch. Start on 24 volts, runs off 12 volts. Had 4, 6 volt batteries and you was suppose to rotate the batteries every six months. Glad those days are over. Since truck engines was 12 volt, somebody always managed to get 24 volt glow plugs and put them in. On a rebuild we would hook them up to a battery before installing them and test them. In a matter if seconds the tip would be cherry red.

I like your math. We have this same issue with 4 cyl Kubota engines used in Altec brush chippers. If the fuel in the tank get low and it's cold the fuel gets thicker and hard to lift. The solutions there is don't let the tank get low and/ or add an electric lift pump ahead of the mechanical one. In your case you might want to add a stronger pump due to the cold weather.

I know this wasn’t the problem with this engine but just because there is voltage at the glow plugs doesn’t mean they are working. I have a small cat engine in a screening plant that won’t start very easily in the cold. I checked the glow plugs just like you did and it turned the test light on but looking into it further I have found that all four of the glow plugs do not have any internal resistance so they are not working. Great video and I do like your trouble shooting abilities. Happy New Year from Haliburton Ontario.

Bringing the new year working on a Cummins great work

I hope you gave the crankcase oil in both engines a visual & sniff test seeing as you identified classic deferred maintenance issues.

Almost all of those little 'solenoid' type pumps generate their pressure/suction via a tiny spring, not the electric solenoid itself. Based on the most common design they have, the fuel passes directly through the piston in them via a disk or ball check valve, and then the ends of the piston are two different sizes from one end to the other. The pressure side is always of a smaller diameter (Say 1/4" diameter) than the spring side (say 3/8" to 1/2" diameter) hence why they are so bad at building suction despite being able to produce reasonable pressure.

Seems they used the generator often enough, just never did any maintenance for it. Most people just never use the generator.

Onan's can be cantankerous even under the best of circumstances Small electric pumps are designed to push, not pull. At least usually, though a small rotary impeller pump can lift a decent distance.

You are without question a very good technician! How ever, your glow plug diagnosis is inaccurate, all you have verified is that you are sending voltage to the glow plugs. You must isolate them and do a continuity test to ground, to verify the heating element is good. Those kubotas like their glow plugs, even in July. Love your videos, keep up the great work!

A good call, backed up with just the right amount of science.

Back again. Remember, the conditions set for your vacuum test have included the fuel piping down to the tank, which has not been exonerated. Hook the vacuum gauge directly to the suction port of the fuel pump without the fuel line connected to get a more reliable evaluation of the pump. This eliminates problems in the fuel line from masking the desired answer.

Very interesting - as always! Thanks Josh, for another year of very informative videos! Happy New Year from Ottawa - Canada.

People are often surprised to find out that, just because a pump can make pressure just fine, does not mean it is able to pull a vacuum well. And I have seen many reasons for a pump to lose the ability to pull a fluid. And just moving the pump lower does not mean it fixes the problem. You have now just changed to a new failure mode for the pump, or it can not produce much more pressure than it did in the original location. And I have no doubts that, with a plugged up fuel filter, that poor pump was experiencing cavitation on the inlet side.The up shot being, the cheap low pressure pump failed. It seems to have hopefully saved the main pump if it was not run dry..... but it seemed to run perfect when bottle fed so, yay for a cheap (ish) repair!

Happy new year and congrats on the 200k subs!

We use those same ice cleats at the paper mill I work at. Pretty convenient 👍

Another thing to check is the return fuel check valve. Even though the lift pump is low pressure, the injection pump will increase the pressure and actually suck fuel through the lift pump. Had a Komatsu common rail system that wouldn't start. Three other mechanics looked at it before me. Turned out the return fuel check valve had a piece of dirt stuck in it. Probably from someone filling the fuel filter from a can.

Thanks, maybe I learned something about my Cummins generator in my RV. I hope I never have to find out but I wouldn't be much on that. Keep the good stuff coming.

Very interesting. When this happens where I work with equipment such as refer bobtails. We check the lift pump located near the fuel tanks.They help get the fuel up to the refer engine. These lift pumps also have built in filters too, the equipment we have where I work does. Great channel

Love your videos, I learn so much from you. Thank you.

Sounds similar to the early Dodge/Cummins 24 valve motors. The boost pump (your transfer pump) was mounted up on the Cummins well above and some eight feet away from the fuel tank. The boost pump would fail which took out the rather fragile VP44 injector pump and then you had problems. Eric, over at Vulcan Diesel, came up with a boost pump relocation kit which moved the pump right under the fuel tank. Most boost pump failures were resolved with that simple relocation trick.

Your videos make me want to be a mechanic. Then I work on a morbark tub grinder at work and remember why I am not. Love the videos man.

Great Video. Really Appreciate your time and knowledge. Have a Happy New Year.

Love the fuel troubleshooting setup you have

I have a customer with a crapload of these little Onan generators with those Kubota engines. I have fought with the fuel systems on them quite a bit. The biggest issues always seem to be the lift pump, lines, or the jetcock that people always seem to twist completely off from either opening them up too much or trying to tighten them like a freaking gorilla.

Happy New Year, Josh! When you mentioned the fuel tank location, from the been there, done that file, I knew the machine had not been spec'd properly causing the poor little fuel pump to be flogged excessively in order to perform its job. But those trouble shooting techniques still had to be conducted -- saying that because one of the commentors below said you should have done that initially. Years ago, a fellow mechanic noticed my successful repair on that issue and thought he would just replace, it turns out, a perfectly good fuel pump, perfectly good fuel filter, perfectly good air filter, and eventually a perfectly good fuel pump without discovering the base cause, which was a shop rag rapped around the pick up tube in the fuel tank. Ouch.

Ohhh thank you sir. You might have solve my problem with my Mitsubishi 8DC9 engine that is hard to start.

This is a very interesting place to put a generator in that type of bus chassis. Normally they're mounted in the skirt. I'm going to go have to measure my bus now to see if I can do the same thing.

Good job on troubleshooting the problem.

A cheaper alternative to that little diesel-powered heater is to go and find a used RV furnace. They are self-contained, most are universal mount (any side up) and runoff 12 volts which with the addition of a propane tank, battery and some flexible aluminum dryer ducting can be made into very handy portable heaters.

Whoopee! A new ape video on January 1. Happy new year buddy!

Happy New Year Josh. Best Year ahead man. More destruction. The engine was consuming oil and coolant. Oil changes were being done on time. It was not enough though. Thank you for the shout out man. I know it was awhile. 👍💪🍾🥂🎉🎊💫🌟

i am picking up an old mercedes v12 from the 90s. wish it was this simple to work on.

Personally I'd put the pump down by the tank. When onan built it they didn't plan on the tank being so far below it. Especially a problem when the fuel gets cold. I tried to look up the heater only to find the link couldn't be found.

Excellent.Love your videos

When I worked in coach care at Cummins, we had a bunch of horse trailers and campers that had gems added in offer places. The livestock trailers they were always on the roof, we had to add in li e pumps down low near the fuel tank to push it up to the stock transfer pump. Just changing pumps on the gen wouldnt last long because the the vacuum on the supply side would wear them out

The best way to check glow plugs is with a clamp-on DC ammeter. Checking for voltage isn't enough. If you don't have such a meter you must disconnect the conductor to each glowplug and (a) check for continuity with an ordinary ohmmeter or (b) touch a 12V wire to the terminal to see if there's a spark. Often you'll find some plugs are OK and some are burned out. This makes for mysterious slow-starts that are hard to explain. If one is burned out, always replace them all.

Good analysis

Very good video. Thanks. I think you found the problem. Did you consider bad suction fuel lines collapsing while pulling the fuel or maybe something blocking the end of the line inside the tank?? 🤔 I have found plastic bags and other junk inside the tanks producing intermittent "no start" or "stalling" issues.

I have a Westerbeke 10K in a boat. The little electric pump goes bad every 2 or 3 years. When I bought the last one, the counterman told me it would last a lot longer if it was pushing rather than lifting. It would be a lot of trouble to change, so I just carry a spare pump. They have been only about $50 to $60, but who knows now with the inflation we have.

Sounds like the primary pump has exceeded the partial pressure of the diesel fuel in the tank. 5 feet of hydraulic head seems like a lot to pump against. The diesel fuel is cavitating. The Onan generator primary pump may not be designed to pump from that distance. A tank pump would solve the partial pressure problem. It's not air in the line but vaporized diesel fuel.

Thanks for sharing

One thing I ran into with RV generators is the pickup tubes in the tanks are a little higher so that the main engine will still have fuel. So below 1/4 the genset won’t run.

This was awesome.

If the main fuel for the bus is below 1/4 tank, the generator will suck air. It's a safety feature so you don't run out of driving fuel

Great video 👍

I don't know if they do it with the diesel generators but it's fairly common practice for auxillary diesel cab heaters to have a shorter pickup tube in the fuel tank so The operator doesn't make the mistake of running the vehicle out of fuel by running the heater.

What that generator running.. cheers good to see you mate 👍

We a number of small engines with electric pumps we always keep the pumps low near the fuel tank

Happy new year

Snap on 17mm (FRXM17) works for those middle fuel lines. Other brands may work but that's the one I know for a fact does.

For the ones in the middle I used a special socket, kinda like an injector socket but thinner. Can’t remember the PN, I borrowed it from my coworker he used to do tons of CAT generators before coming over to big red.

Local to you cat mechanic, worked on this same bus and same generator, it wouldn’t run last time and it was the fuel shut off solenoid, funny seeing this pop up

An Onan generator won't start? Pull it harder! Sorry... look up Onanism. Great video. I just had to interrupt and say that.

You can get to those fuel lines by using an open end wrench from the top. Put something through the closed end to rotate it like it was a T handle.

You can add another pump down at the tank as a lift pump and give relief to this pump as pumps do not "suck" very well they push

I've worked on plenty onan Cummins just like that. Seen quite a few minor fuel issues like that too. We ran a 6 cyl onan off a windshield sprayer pump temporarily to replace the faulty low pressure f pump, same prob as u got here. We hooked it up backwards at first. Do mind the return fueling line when u get the new pump as that causes a no start. That's a long run of hose to pull fuel for sure. Maybe it needs two little pumps in series, and check valve(s) if none already. Solid machines of course w Cummins fully mechanical. Companies/institutions tend to buy oodles of the same brand gens when they get a huge package deal I suppose. Lots of commercial and industrial go cummins small to big. Cheers

master of physics. great look on things. these diags, gotta feel good and kinda shitty right? you found all those fittings and did the testing that needed while many parts replacers would've put a filter and fuel pump on and then shit works. either way. thanks. Glad to remind myself about the vacuum "pull" side of fluid pumping.

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Hey Excellent video. I would think generator would have its own tank. So it’s fuel pump been struggling since generator install. I don’t mind little cold weather but that’s cold.

i would also put a diode inline a one way valve to keep the full from pulling back down into the tank.

Highly recommend the Vevor heater to field techs, you can “borrow” some fuel from whatever you’re working on if needed

I suppose when you get the new pump you can test it for what vacuum it can pull but that is a long ways to lift fuel and of course the fact is the generator/engine engineer and the bus design engineer were never in the same room so these are the sorts of built in failures that are waiting to happen. Just one of those things you can advise the customer of and go from there if they want you to relocate the new pump or try leaving it as it is. This reminds me of my John Deere combines, the fuel tank is lower than the engine by a fair amount and they have a small electric pump mounted in a location that is level with the bottom of the fuel tank, also aids tremendously in priming the fuel system after changing the engine mounted fuel filter as it would be impossible otherwise.

I have found that a lot of electric fuel pumps are very poor on the suction side. I would suggest putting on a new fuel pump and relocate the fuel pump down by the fuel tank. We have noticed this on motor homes with a long draw on the suction side of the fuel pump. Hello from north east Montana. 10 miles from the Canadian border.

I've replaced a few of those pumps, almost alwa6s the pump and at least they are cheap

In my experience those little electric pumps are a lot better at pushing fuel than trying to pull it. Most fitting instructions I've read say to mount low and as close to the fuel source as possible...

Infact this is the first time I see this left pump with Cummins, I always deal with mechanical left pump .

Brilliant engines thos Kubotas but they do like a good fuel supply and being idi they really need glow plugs to start even in warm weather

Elementary my dear Watson.... Vacume

Must be a fuel pump made by Lucas. That's one of the things they manufactured that didn't suck.

11:50 remind me cracking old fuel line getting air suction in line just following it all way to tank and check for any broken line need replaced it so it will stop any air getting in it

2-4 psi seems rather low too. That would be ok for a carburetor. For a diesel I'd want to see closer to 10 psi.

The little fuel pump that sucks is a Ketering (Solenoid) style that has nothing more than a plunger inside a coil that turns ona dnoff quickly to move the plunger. These are very simple pumps designed for low-head appliacations and in many cases like this, poor choice. What you have missed is there is a crack in the fuel line somewhere neart the engine/pump as it dide pull some air into the line that was under vacuum. The best solution would be to re-engineer it to fix the screw-up of the muppet who put a genny that high up and away from the fuel. What is needed is something like a Carter fuel pump (5-7PSI) or better still, the Carter Black (13-15PSI) which both can do 100GPH however, these build good pressure and great for any diesel that relies on mechanical or solenoid style pumps. Put the Carter down near fuel tank witha intake screen filter (the Just-in-Case filter), feed fresh line all the way to the fuel filter on the genny then fresh line from filter to Injector pump. Herem I would put in a small T-piece with restricted size nipple that has a smaller bit of hose going to the return line off the injectors. This now means the lift pump can push pressurised fuel to the system and a "controlled leak" will purge air back to the tank before it settles down into the IP. Sight Glass up at controller leak T-piece would also be handy for water detection.

I have a Westerbeke generator on my boat that has the same symptoms. It ran slowly for about a minute, then died. Hasn't restarted since. Fuel doesn't squirt from the injector fittings, it seeps while cranking. Filters have been changed. I was going to pull the injector pump. I'll try the fuel pump next, instead. Provide a closer fuel supply first, and see what happens.

I do prefer the TK FUEL pump for the CB units that go on the truck units, not for the trailer units.

😎👍

I wonder if the inflow of fuel at the fuel tank is obstructed with gunk. Is there a pre-filter from the tank?

I have that same Onan 10HDKAG generator on my firetruck, and it’s top mounted about 6’ above the fuel tank also. The Woodward solenoid is strictly for the fuel shutdown control the governor is actually the other lever that’s fixed for 1800rpm operation. I agree with low vacuum on the suction side, Did the pump fix your issue?

Not sure your glow plug test with test light confirms the glow plugs are heating up. 3:15 in the show now. Test light test will show that power is available at the glow plug but a current flow test of the circuit is really needed, correct?

Is there not a check valve inline with the fuel supply to keep it from falling back to tank ?

LONG time viewer here! I have a GMC C8500 with a 3126 and MT653. Awesome truck but 2022 was not its year. So quick question! I have had an intermittent stalling issue. No smoke, no stumble, just like I turned the key off. Sometimes when coasting with the converter locked it will refire, sometimes running for hours, other times immediate stall then no start for 10+ minutes. When unplugging the IAP, it used to de-rate but run perfectly for months without stalling, but it would only start with the IAP plugged in which is opposite what most would think. Now it stalls whether IAP is plugged in or unplugged. Every 10sec-10 min. Does this sound IPR related, like the failed iap when unplugged worked until the IPR failed? Here's why I don't think HPOP. When it runs right, it runs flawlessly. Sometimes for 12hrs at a time. Great power, quiet, no smoke, great fuel economy. Fresh oil change and fuel filter. Tank is clean. Seems to "lightswitch" on/off to be fuel related. When it quits, it's immediate. Silent. Like key switched off. My company grew last year much quicker than expected and the backup trucks aren't done yet, I need 2 more weeks out of this until I can take it down for maintenance. What're your thoughts? Only person I know who would have worthwhile input!

I hated working on Onan generators when I was in the army

How does all that air being sucked in the fuel line get purged? I think you have an air leak on that fuel line and when you pull suction on it you're pulling air into the fuel as well.

Had same problem with the APU.(new inline fuel filter and big one) and Installed a new manual pump ( not designed for electric), still nothing ( fuel wouldn t move in clean line) . then I installed an electric one to help pushing the fuel and take all air out - still nothing , then I disconnected the lines that goes to the Inj and no fuel came out .. I found they both were cloged at the bottom of the line (close to the pump ). After uncloging, I pushed the fuel with the electric pump and now finally hot fuel traveling thru the line toward injectors ... still no start , but I noticed the glow plug light was " on" on the APu module/controller. It looks like now I have to see if that's the problem.. is getting frustrated since some bolt broke due the rust and winter salt( APU sitting on the buttom of truck )

install another low pressure pump near the fuel tank and that will solve any future problems .

From the beginning of this video, I was thinking I’ve never seen a generator mounted up so high on a vehicle. If it were me, I’d replace the pump and relocate it much lower so that it pumps up to the engine and filter.

Missed this vote. Keep shop noise

And change the fuel line as the rubber collapses and restricts giving the electric pump a hard time

Weird that Cummins used glow plugs instead of an intake heater.

Check valve

I guess the people that had that bus don’t really care about maintenance much. And It always seems the same people with that attitude wonder why something stops working.

2:50 have you pulled it out and run jumper cable to it to see if heat up (no) so there you dinner lol 2nd that valve controls motor not supposed pull back on fuel injecter pump because that is cutting fuel off to engine when u turn it off it will pull level back cut fuel off you are missing out alot on engine which you didnt know about im engineers i have worked on ton of motor in my life for over 20 years never stop working on them because i still love doing it no matter what i come cross seeing this misunderstanding how engine work i going point you out take it out and test it before you say (they are working) and valve is killer switch should not pull in when starting engine

Break the lines at injectors

Is there any way to contact you about a fuel pressure issue?

There should be another pump at the tank.

Still 2 minutes from the end, so I don't know the outcome. My experiences are from the vacuum pumping industry, and I can emphatically state that little leaks in a vacuum system are very serious to proper operation. Any introduced air, when placed under vacuum, immediately expands and causes all ,kinds of problems. If this fuel system were a circulating type, like vehicles generally are, small leaks would be self-purging, as the amount of consumed fuel is only a small fraction of the circulating fuel.The dead-end fuel system must purge through the injectors. Just FYI, I would view the vacuum bottle and an external pump as an invalid test because the vacuum pump capacity may greatly exceed the fuel pump capacity and the vacuum bottle gives an air disengagement space not present in the fuel system. Conclusions drawn from this test could be just as easily misleading as helpful because of unequal conditions. This aside, I would view the bubbles in the fuel line as cause for investigation in that direction, especially with a rubber supply hose As fuel system components are generally less expensive than lost work time, and hose especially so, I would replace everything from the lift pump back to the tank and then give it a good capacity test with something like an oil burner pump or one of those Harbor Freight drill pumps while watching for bubbles. Also, current present at the terminals of the glow plugs is NOT a definitive indicator of working glow plugs. Disconnecting the glow plug power supply and doing a continuity test is much more reliable as shorted plugs are much less common than open plugs. NMow, back to the video for the conclusion!

Fuel cap blocked?

pumps always push better than they pull.