Generator - Hard to Start

[Eric M]

Hi All,

Looking for some advice on my generator which has become hard to start. Here are the details:
Mid 90's vintage 5KW Northern Lights Gen set.
Controls include 2 rocker switches, one for pre-heat, one for starting/stopping.
Owners manual says to pre-heat for 10-12 seconds then start.

When I purchased the boat in Aug 07 the gen set would always start within a few seconds of pushing the starter. Over time it has gotten harder and harder to start.

Typical symptom is as follows:
Starts in 2-3 seconds, but dies quickly (<5 seconds)
Wait 10-15 seconds
Re-start in 2-3 seconds and dies again, maybe after coming up to half speed
Wait 10-15 seconds
Re-start and comes up to full speed and operates fine until shut down.

A hot re-start and it starts without issue.

I have changed both the primary and secondary fuel filters with no impact on the situation.

I am wondering if maybe one or more of the glow-plugs have failed?
I searched the archives for "glow plug" and didn't come up with anything related to this topic so wanted to ask for advice on the issue, and specifically on troubleshooting glow plugs.

Thanks in advance,
--Eric

 

[Don S/V ILLusion]

There is a lot of advice on how to test glow plugs which you can find searching the internet. Simply stated, their characteristic resistance is the easiest waty to determine their potential to sufficiently heat the cylinder(s).

 

[Rich Stidger]

Don is correct regarding the resistance of the plugs being an indication of their potential to operate. Here a a couple test methods:

A simple way to quickly check for working/dead glow plugs is to turn on a lamp that you can see near the control panel. When the Preheat switch is activated, you should see the lamp dim slightly. No dimming means that the glow plugs are not operating a all. Of course this will not tell you if one or two out of three or four glow plugs are bad. It is a all-or-nothing indication.

If none of the glow plugs seem to be activating (no dimming of the lamp at all), I would check the solenoid that switches power to the plugs. Your rocker switch will only close the solenoid and the solenoid will perform the actual switching of power to the glow plugs.

You should be able to hear/feel the solenoid pick-up when the preheat rocker is depressed. You may need an assistant to operate the rocker switch while you feel/listen for the solenoid. I think it is unlikely that ALL the glow plugs are failed, so the solenoid or wiring is a better suspect.

The glow plugs can be tested individually as follows:

The easiest way is to use a clamp-on DC ammeter and measure the current draw on each plug. The current values should all be about equal. Take the reading on each plug after energizing for the same number of seconds. The current will decrease as the plugs heat up.

If you don't have access to a clamp-on meter, disconnect the power wire to each plug. Secure the wire ends so a short won't occur. Using an ohmmeter, measure the resistance of each plug when COLD and write it down. I would expect a reading of about one ohm. Then start the generator- this may be difficult with the plug wires disconnected, so you may have to re-connect to start.

Run the genset until at normal operating temperature. Stop the genset and disconnect all the glow plug wires and secure as before. Restart the genset and while running measure the HOT resistance of each plug.

Compare the hot and cold resistances. The hot resistance should be much higher (5-10x) than the cold resistance. If either the cold or hot resistance is open, that is a bad plug.

 

[fredr]

Once the engine starts the glow plugs are not a factor.
The engine is a pre combustion chamber design and needs a charge of heated air to get started, once it runs, even for a few seconds, they have done their job.
The engine is not holding fuel in the lines over night.
You may have air getting into the fuel system when the engine sits for an extended time.
Air getting into the fuel system and allowing fuel to run back towards the fuel tank.
This could be at a hose connection, or a return fuel line.
It is very possible the fuel punp is failing to hold fuel up stream, between the fuel pump and engine.
Take the fuel lines off the lift pump and hold your thumb over the inlet. Pump the lift pump lever and see if it hold suction.

fredr

 

[Franklin]

Back when I was in the army and working on Diesel engines that used glow plugs, I'd just take out the glow plug leaving it connected to the wire. I'd spit on the tip. I'd then hold the plug with pliers and touch the pliers to a ground like the engine block and ask the operator to turn on the glow plugs. If they were working correctly, the spit would sizzle and eventually smoke as it dried.

The good thing about doing this is that you would find plugs that were on the edge of busting (tip mushrooming). Once they exploded, it was very difficult to get them out and many times we had to remove the head to get them out as the plug would bust off inside the cylinder, so I was always happy to check them and find ones going bad.

I was very surprised to find that Yanmar has built a diesel engine that doesn't need glow plugs. Why can't American companies build them like that?

 

[fredr]

Well, the Yanmar is a ... half breed, I guess.
It has a pre combustion chamber but it is more open to the cyl / piston.
The heat from compression doesn't go far into the cyl head where it looses its heat.
Pre combustion chambers accelerate combustion beause the compressed air travels through a slot, or port that has a small opening. This causes the air to increase its volocity. In the top of the combustion chamber is the nozzle, and glow plug. So the rushiing air mixes with the fuel more rapidly giving a higher RPM engine. It sounds strange but works fairly well. Yanmar has a type of pre combustion chamber yet still has high nozzle opening pressures, 2800 psi, to atomize the fuel better.
You can put a drop light , in a safe manner, on the intake and leave it there long enough to heat up the air intake manifold and the engine would start without using glow plugs. They are just a starting aid.
Although, some engines have them cycle on a little longer after the engine starts to reduce smoke in very cold temps.

fredr

fred

 

[Joseph Shirley]

I agree with Fred. I think your problem is fuel. My Kobota starts without glow plugs but my key switch allows me to run my fuel pump for 5 to 10 seconds before I turn it the other way, and crank the engine. You should be able to do something similar.

Joe S

 

[Eric M]

Thanks all for the replies - I'll post again when I discover if I am having a loss of fuel prime or glow-plug issue.

 

[AXEL]

I was having a hard time keeping my engine running at the begining of the season. The problem turned out to be a clog in the fitting on the fuel tank. I removed the fuel line from the fuel filter to the tank and blew in. It was very difficult to blow bubbles in the tank. My fuel tank has a 90 degree fitting with a shut off on top. I stuck a pipe cleaner in the fitting and cleared the clog. Problem solved! Check it out on your boat.

 

[Franklin]

If you want to know if it's a fuel problem, try bleeding the fuel line where it goes into the engine. Take the hose off and put it in a glass. Ask somebody to turn on the engine but don't start it. Assuming you have an electric pump, it should start pumping into the glass. Hold the fuel line below the fuel to check for bubbles. If you have bubbles, you are sucking air in the line before the pump. If fuel comes out strong and no bubbles, then it's not a fuel problem.

 

[Franklin]

Ooops....just went back and re-read. It does sound to me like a fuel problem after the pump as stated before because once you get it started, even for a second, the cylinder is hot enough to continue to fire. So check the fuel line between pump and engine and also the clamps. If it's anything like my generator, it's mostlikely a loose clamp where the fuel line attaches to the engine, but don't forget to check the clamp at the pump.

If the clamps and hose are good, then the engine must be letting in air someplace and it is the pump that is worn out....replace pump. Napa has the pumps at half price of the marine stores.