Generator hard start

[Kim Prowse]

Our Kohler 8kW generator uses a Yanmar 3TNE74C-EKM. It has a hard start issue that is very hard to diagnose. It takes 6-8 attempts to start and getting worse. When it finally starts it runs great with no smoke or unburned fuel in the exhaust. Following is a list of things that have been done in a failed attempt to diagnose the issue:
- Injectors rebuilt
- Fuel solenoid tested
- Fuel pressure tested
- Fuel pump replaced
- Fuel lines replaced
- Fuel valve packing tightened at the tank
- Primary and secondary fuel filters replaced
- 12V wiring tested
Has anyone else had this issue and what did you do to correct it? Thanks for the help.

 

[rgano]

Here is what I learned from an increasingly hard starting 3.5 KW Nextgen generator.

A diesel needs fuel, air, and compression to start and run. In my case the glow plug needs to be working properly. It sounds like you are missing compression and/or maybe the glow plug, if so equipped.

After doing pretty much what you have done in the way of troubleshooting, the factory rep suggested that I grab the big belt which drives the electrical end from the one-cylinder diesel. Guess what? There was literally no resistance which I should have gotten on the compression stroke. That could have meant a stuck valve, but it was far worse than that.

Tear down revealed severely corroded valves, their seats, and the piston top due to water intrusion which in turn was the result of a very poor Mainship factory installation of the exhaust system. I corrected the exhaust system run and got enough insurance money to completely overhaul the genny. Then the shipping company dropped and dragged the rebuilt genny on its head, and I would not accept it. The shipper ended up paying for a brand new electrical end giving me an essentially zero-hour generator.

Six months after removal of the corroded generator, it is back aboard and jumps into life better than when I bought it new in 2018.

Your genny doubtless has more complex controls which could be interfering with starting, but it certainly begins to sound like lack of compression. See if you can find a way to manually spin the crank shaft to give a clue about compression or just run a compression test.

Best of luck and hope to hear of your great success.

Oh, and welcome aboard! I am sure you will get lots more advice here about you particular generator.

 

[Comodave]

Welcome aboard.

 

[kwmeyer13]

My 34’ Pilothouse has a 3.5 Nextgen generator that was temperamental. The run solenoid was not pulling in all the time. I changed it out and that solved the problem. I have had no issues since. I realize you have a different brand but thought this problem was worth mentioning.

 

[rgano]

My 34’ Pilothouse has a 3.5 Nextgen generator that was temperamental. The run solenoid was not pulling in all the time. I changed it out and that solved the problem. I have had no issues since. I realize you have a different brand but thought this problem was worth mentioning.

I had thought MS put 5.5 NextGens in the 34s. I suppose the new buyer could specify either that or the 3.5 like I have in my smaller 30 Pilot.

 

[High Wire]

Welcome aboard. You need a compression test. That takes about an hour of diesel mechanic time or do it yourself with the proper equipment.

 

[SIBERNUT]

Should note you can't do it w a car gauge, & you'll need the correct adapter.

 

[kwmeyer13]

I had thought MS put 5.5 NextGens in the 34s. I suppose the new buyer could specify either that or the 3.5 like I have in my smaller 30 Pilot.

I think it was dealer’s choice on the size of the genny.

 

[SteveK]

The genny on my current boat would turn over no problem but would not start. PO confirmed that his tech was on the way in a few days and will have it fixed. He had not used it for at least 3 years. Kudos to my mechanical inspection tech who got it started, it has started and ran fine ever since. All it took was tapping on the valve stems to free them up from the open position they were stuck in after the engine was last stopped.

 

[Turtle Blues]

Believe that engine has glow plugs?
What is your starting sequence to hold in glow plugs before engaging starter?
Have you removed a glow plug and energized to confirm working? Tip should glow red hot?
If I'm wrong about having them please disregard.

 

[Duetto]

i'm skeptical of a major problem. if there was something really wrong, it wouldn;t run well once it started. what does the 6-8 times mean(i.e. starts and stops or cranking). we have a genset whose fuel valve died and exact replacement was no longer available. bought the "new" refit kit. where once it fired right away, now cranks a lot but starts. kit seller admits it's not quite right.

what was changed? a great genset doesn't go to a mediocre one just because.

 

[Lepke]

If a diesel has to crank for a long time, it's usually low compression. Air when it's compressed rises in temperature. Each compression revolution raises the air temp and warms the piston and sleeves. When it gets to about 500°F the cylinder will fire. A new high compression engine might fire on the first revolution. An old engine maybe 10 or more turns. The problem is worse in cold temps because your starting from a lower temp but still need 500°. A slow cranking engine doesn't raise the temp as well as a fast cranking engine. Have a good battery. A couple solutions are glow plugs or if available, #1 diesel that has a lower ignition temp. One fix is to point a hair dryer into the intake while cranking. Another is add a block or pan heater. If you start from a higher temp it's easier to achieve 500°.
Low compression can be from wear, but also from glazing the cylinders from long hours under a light load. Small engines run at higher rpm making glazing easier. In America an 8kw will run at 1800 or 3600 rpm. Heavy duty generators run at 1200 rpm and can run under light loads for decades.

 

[Andy G]

I have little knowledge about generators. We have a 7KW Gen Set & have noticed that it is also taking more cranks to get it to spring into life, and like the OP's generator once it gets going it runs faultlessly. Is this a general sign of old age?

How many generating hours can you expect out of a reasonably well maintained unit?

 

[rgano]

i'm skeptical of a major problem. if there was something really wrong, it wouldn;t run well once it started. what does the 6-8 times mean(i.e. starts and stops or cranking). we have a genset whose fuel valve died and exact replacement was no longer available. bought the "new" refit kit. where once it fired right away, now cranks a lot but starts. kit seller admits it's not quite right.

what was changed? a great genset doesn't go to a mediocre one just because.

I would have been of the same opinion until my catastrophe (poor exhaust system) as noted in my post above. My very corroded generator ran quite well under load with no smoke or overheating, ONCE it started. The starting gradually got to the point the OP is experiencing with his genny which is requiring multiple efforts to start. And then one day, it simply refused to run due to no compression due to the corrosion which took about four years to develop with ever increasingly dire oil sample reports from Blackstone every 20-40 hours of operation. I bet I have one of the most well-documented cases of this problem in the history on man!

 

[mysweetLord]

Your engine has glow plugs but Kohler did not wire them in for operation unless spec’d that way.
Check that the fuel return pipe, inside the tank is immersed in fuel.
Air can migrate back if it’s not in fuel.
Other than that, rig up a short section of clear tubing and temporarily install it in the suction side of the sets fuel supply.
Looping a high spot, so air can accumulate may reveal surprising results.
This may take several days or visits to the boat in order to get a good test.
If all that fails, install a temporary test fuel tank right next to the engine. Isolate the vessels fuel system. That will definitely get you in the ballpark re: prob on boat or engine.
God bless ya

 

[Southern Boater]

……….. It takes 6-8 attempts to start and getting worse.

If you have a “water trap” or “pond box” muffler, the same thing, different names, be careful when doing repetitive starts, just winding it over. Unless the engine starts within a reasonable time frame and forces accumulated cooling water out of the muffler, there is potential for back flooding.
These genset mufflers have small capacity and can fill and run back up into the exhaust elbow/manifold creating sea water ingress into the valve train and hydraulic lock the engine, or just create corrosion if left

I undo the bung at the bottom of the muffler and and let the water drain into the bilge if doing multiple starts and knowing the engine is not going to start.

 

[Trawlerman]

You wrote "Our Kohler 8kW generator uses a Yanmar 3TNE74C-EKM. It has a hard start issue that is very hard to diagnose. It takes 6-8 attempts to start and getting worse."
But did not describe what the process is like. Do you crank and crank and nothing fires, or what? If, for example, each time it cranks a bit each time you try starting but then quits cranking, the issue is almost surely the start solenoid. The donut shaped ring that makes the contact closure for the starter current gets pitted after time, and needs replacement. On the other hand if this is not the case, then what do you do at the end of each "attempt"? The only other possibility that I can think of is that there may be a relay that feeds the preheaters that is intermittent. More info is needed to really give a decent potential diagnosis. Hope you find the answer and please let us know when you do.

 

[Trawlerdream]

Had the same problem on our MS390. Generator only has 150 h after 23 years. Previous owner said it always had been hard to start. It required 2 x 8 second cranking.

I wired in the existing glow plugs. I use the glow plugs for 10-15 sec before
Attempting to start. And now the generator starts after 1-2 sec of cranking. And that is temps around 36-40.