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Old 17-11-2019, 00:35   #1
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Onan Diesel Geni wont start

Hi,
Our Geni is an Onan 4.5 KVA circa 2005
I always start and run main engines and generator every time we are on our boat.
This time the geni didn't start, it turns over but wont start, I changed the fuel filter just in case but no cigar.

Is it possible that the 2 glow plugs are shot?

I put a multi meter on the glow plug it shows 12.5 volts and drops to around 10V when cranking.

What else could cause this other than the glow plugs?

Any advice on what to check and how to check would be great
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Old 17-11-2019, 03:38   #2
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Re: Onan Diesel Geni wont start

You have chased all the air out up to bleeding the injectors? My onan has linking led fault code light in the start switch that can be deciphered for the sensors/required elements that will not allow it to run.
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Old 17-11-2019, 16:18   #3
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Re: Onan Diesel Geni wont start

First turn off the raw water intake to negate the possibility of getting raw water in the cylinders from dead cranking. The fuel system is the usual suspect and you need to have a smooth bubble free flow of diesel from the bleed points. Once this is established, loosen the high pressure lines at the injectors and try cranking again, you should get fuel at each nut...... no fuel here is a definite no start so try venting the bleed points again and then try cranking again. If still no fuel at the injector unions, there might be a problem with the safety shutdown circuit, possibly a failed circuit switch, there are usually 3. Low oil press switch: high temp coolant switch and mixer elbow temp switch. Also check the run solenoid and manual shutdown. If any of the switches have failed in the activated position the engine may not respond to startup override command.
Don't forget to open the seacock once you get her to fire up again.
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Old 17-11-2019, 18:00   #4
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Re: Onan Diesel Geni wont start

I have same generator of same vintage in my boat. When I bought the boat it did not run...... engine wanted to run but just would cut out. P/o had yard look at and have an estimate of 8,000 to repair saying it was the electrical head. I figured it was worthless as I can get a new one for that. When I pulled engine it turns out that all it appears to be is a broken belt amiture. Belt is on the back side..... after you check all the easy things mentioned above check the belt.

Good luck!
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Old 17-11-2019, 19:20   #5
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Onan Diesel Geni wont start

You need to check glow plugs by checking resistance, like a light bulb, if there is no resistance, itís burnt out, and yes Iíd say itís very possible and among the first thing Iíd check.
My experience with them is when one goes, it seems the other gets more power and also burns out pretty quickly, and or maybe itís that until they are all burnt out it will start, because Iíve often had all glow plugs burnt out when I had a problem.
But as was said, turn the water off now, before you flood the engine.
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Old 18-11-2019, 10:50   #6
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Re: Onan Diesel Geni wont start

first check your battery, it may turn the generator but does it have enough cranking power to start it, you can check with your volt meter
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Old 18-11-2019, 10:59   #7
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Re: Onan Diesel Geni wont start

Hard Starting Gen SetSome times best to start with Basics. It is diesel all it needs to fire is Compression ( to heat the air) (air to be heated) and fuel injected at the right time.
I olden days when a Bulldozer would not start in the cold you stuck a loosely crumpled newspaper up the Air intake (having removed the air filter) lit the newspaper with your Zippo lighter and walked around and climbed up and hit the starter switch --- and nearly always Rumble Rumble. Away you went. Novices sometimes have trouble bleeding effectively it is necessary to get ALL the air out so it is a two handed operation
one hand wriggling the little pump lever and the other hand on a wrench so that you can tighten the fitting with the wrench WHILE clean airless fuel is leaking out. OK not half a second later. Sorry to sound like a school teacher but it is the DETAILS that count!.
So (1) Have a look down the intake make sure it is clear and dry (Paper Towel)
(2) Loosen the lead at the injector ( the highest one) hand pump make sure you have fuel.
( now my personal #3) Get a piece of Sand paper and disconnect the ground strap that grounds the block both ends make them shinny metal and reconnect them .
Do the same to the connections to the starter be fussy, Ok try again,
(4) Now you have hopes that you have nearly as much voltage at the starter as you have at the battery it should start ( Those connections are sleepers they are rarely exposed and can build a totally isolating film in a couple of days for no apparent reason.
(5) Still no start - Bleed the fuel system. Personal experience is glow plugs do not matter that much unless it is down below freezing and the engine is old and the oil has drained off the rings so the compression is low = cool fuel No bang! Good luck all you need along with Air-- Fuel-- and Compression, Mike Pope
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Old 18-11-2019, 12:42   #8
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Re: Onan Diesel Geni wont start

We have a 6.5kva Onan, with a Kuboto 3-cyl. diesel. We've had a lot of issues with the fuel shut-off solonoid....if it does not open ALL THE WAY, the fuel valve does not open the eng does not get fuel, and will not start. Check the solonoid, and see if it is opening fully (just push on it when your starting). IF it moves even just a little, that's your problem. Or if it doesn't move at all, check the power and ground lines to it...we've had them vibrate loose and/or break the wire right at the crimp-on connector.....fix the connection and waalaa...she works!
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Old 18-11-2019, 12:55   #9
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Re: Onan Diesel Geni wont start

Sorry....hit the wrong key! From my experience, if it's been running, and now suddenly won't, Air in the fuel lines is a possibility, but I'd be surprised if that's the cause now. Same with the glow plugs.....as a matter of fact, we didn't know we had glow plugs installed and didn't use them for the first 16 years of ownership! We use them now, and it does seem to make for easier starting, but ours started just fine, regularly, for 16 years without them! From our experience, if this is an all of a sudden event, I'd look for a loose/broken wire, the fuel solonoid, or a popped c/b or mis-set switch in the start control logic.
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Old 18-11-2019, 13:15   #10
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Re: Onan Diesel Geni wont start

When a Diesel engine just flat wonít start Iím afraid there is no sure way of having someone say do this or do that and you will be problem solved.
Things like this can have many causes and sometimes several that have mounted up.
You need a good reference manual some help maybe but you have to start at the bottom and go up a decision tree one branch at a time. Sometimes with a knowledgeable history on a particular engine you can go straight to the most frequent cause and be lucky.
Do you have sufficient cranking voltage
Does the engine turn over
Is fuel pump putting out
Are glow plugs ok.
Are any solenoids passing power when they get power
Is computer board functioning
Is electrical generator portion putting out AC voltage. If not many engines will crank but not run.
Are all the safety switches working. Low Op, overheat switch, exhaust temp switch
Etc etc etc
Need a multimeter and a reference book. Look at YouTube for pointers on specific issues. If you canít go this route then maybe best to get on the phone and make some calls for a service tech. Watch and learn.
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Old 26-11-2019, 00:08   #11
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Re: Onan Diesel Geni wont start

Hi all ,
Thank you for the feed back/suggestions.

I have installed two new glow plugs and still not staring.

Checked the old ones with the ohm meter and they measured 1.1 ohms

Then I had a friend have a look , he cracked the top return lines from the injectors and there was little flow.
He then cracked the low section and had fuel pressure there.

How do I bleed the fuel system as there isn't a hand pump set up just electric pump that I guess should prime the system.

Thanks again for all of your advice

cheers James
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Old 26-11-2019, 03:19   #12
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Re: Onan Diesel Geni wont start

You crank it with the starter to get the HP fuel up to the injectors. As posted previously secure the SW intake first so you donít back flood the engine with SW while you are turning it over repeatedly. Stop it immediately if if starts and get the SW back on, otherwise you will likely ruin the impeller running it dry, also the gen will likely sense the lavk of water and shut down.
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Old 27-11-2019, 07:50   #13
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Re: Onan Diesel Geni wont start

Opening the return lines on top of the injectors is not a usual step in bleeding air from a diesel fuel system but venting at the injector pump supply is very useful. I'm still not clear about whether you have fuel coming out of the high pressure lines at the injectors.... you will only get this while cranking the engine holding the manual switch that over rides the automatic shutdown as for a normal start. If there is no fuel from those pipes you have no hope of getting it to run and will need to check the operation of the engine shutdown device/solenoid. If this is not the culprit, it's possible that the fuel rack in the injector pump has stuck in the shutdown position. All of the above statement assumes that the low pressure fuel supply is adequate and bubble free.
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Old 27-11-2019, 17:15   #14
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Re: Onan Diesel Geni wont start

A diesel needs fuel and air to run. In addition to the fuel shut-off solenoid I wrote about earlier, we've had a series of issues with the Onan engine-mounted fuel pump. We finally got a good one, and it's been working OK, but NAPA sells a very reasonably priced faucet electric fuel pump (free-flow without power). Bought one and installed it on the fuel line leading to the genset. If there's any question of lack of fuel, I switch that little pump on and I know there's fuel getting to the injector pump. The fact that your Onan was running, and now suddenly has these issues, I don't think glow plugs are your issue....I think you'll have better success if you can confirm your solenoid is working correctly (fully opening and staying fully open) and are sure you have a fuel supply to the injector pump (ie, the electric faucet pump).
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Old 27-11-2019, 21:19   #15
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Re: Onan Diesel Geni wont start

I had a starting problem with my generator (1 cyl Entec West ). It cranked and and cranked, but would not start. It turned out to be the fuel shutoff solenoid. The Entec generator has sensors (exhaust temp, water temp, oil pressure) that will close the fuel solenoid if those parameters are out of spec, shutting the engine down. It could be that the solenoid is working, but a sensor is malfunctioning, causing the solenoid to stay closed.

Hold a gasoline *damp* rag on the air intake (filter removed). If engine fires briefly, you very likely have a fuel problem (air, malfunctioning fuel solenoid). Be careful to not let the rag get sucked into the engine and you don't need a lot of gasoline, just damp.

If you suspect fuel delivery problem and you've ruled out air in fuel lines, can you bypass the fuel solenoid to deliver fuel?

I don't know if your generator has these sensors or if you can easily bypass that solenoid to test the closed solenoid hypothesis.
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