Generator woes- low compression across all cylinders

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Pau Hana

Commercial Member
Aug 29, 2012
Good Ol' US of A!
Vessel Name
Pau Hana
Vessel Make
1989 PT52 Overseas Yachtfisher
The patient- a KiloPak 12kW genset powered by an Isuzu 3LD1 3 cylinder diesel engine. 450 hours run time. All was working well on our last summer outing, with zero indications of trouble.

In December, I strung up the Christmas lights and then went to start the genset to test everything- but it would not fire. It would almost catch, but no start. I checked the water sep and spin on filter - all good.

On the control box (prime, preheat, start, stop buttons) I noted that the stop solenoid was not operating when the button was depressed. I pulled the solenoid and ran it to 12v direct- seemed to work perfectly. I pulled the fuel lines and confirmed fuel to the injectors.

I finally called in Hatton Marine, as they are Isuzu “experts” (I question the “expert” part…)

Hatton came in and ran essentially the same tests and wanted to replace the stop solenoid, as it was the problem…even though I stated I had tested the existing one and it seemed to test fine. I agreed to the part replacement, and after they installed it, there was still no start.

Hatton then declared that the injection pump was faulty. I sent the service advisor some info from BoatDiesel that showed the 3LD1 has 3 injection pumps. Hatton then compression tested the engine and stated that the genset was dead and needed to be replaced due to an average of 200 psi across all cylinders.

I’m open to ideas from anyone experienced with this type of problem…
It does sound like a compression problem, but possibly fuel. Are you getting grey smoke out of the exhaust while cranking.

The second question is what caused it after 500 hours. If you ran it for long periods under very light load then maybe the cylinders are glazed. If you can get it to start- use a hair dryer in the air intake, run it all day at 80% load and see if that helps.

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Is it throwing any white smoke/haze out of the exhaust while cranking? If not, I'd suspect that it may not be getting enough fuel to the injectors even if there's some. If it does throw a white haze after cranking for a few seconds, then you're likely getting enough atomized fuel to the unit. For the stop solenoid, is this a "power to run" or "power to stop" setup and is the injection pump actually making it to the run position?

If you've got a hair dryer or heat gun handy, use it to feed hot air into the intake for a minute, then crank the gen while still feeding hot air. If it's just a bit low on compression then the hotter intake air may be enough to get it to fire (and you can then assess how it runs).

You also mentioned preheat. Confirm that the glow plugs are actually getting power and check the resistance of them to make sure none have failed. Some engines that rely on glow plugs just won't start without them, especially in cooler weather. That may be even more of a suspect if supplying hot air gets it started and it seems to run fine after startup (not low on power, no unusual smoke, etc.).

Another thought: does it sound like it's cranking at a normal speed? If the battery or starter is bad and it's cranking slowly, that may be enough to cause a no-start and low compression reading. If it's cranking significantly faster than normal, that could agree with low compression.

Personally, I'd be surprised if all 3 cylinders rather suddenly went from fine to low on compression. 1 cylinder from a stuck valve, sure, but not all 3 unless the unit had enough moisture in the cylinders to rust and stick the piston rings.
If you can't trust Hatton maybe give MER a call? It's been many years but I used to tend to the care and feeding of a pair of gens powered by Isuzu 4BD1. MER was my go-to for advice and parts. As i say, it's been years and things change. Don't know if MER still does small Isuzu engines.

Another option is Klassen Engine. Long story but the 4BD1s came from Klassen, sold and installed by Canal Marine which is no longer in business.

Hatton used to be top notch, but I hear from friends still working the waterfront things have changed there.

On the subject of cylinder glazing. I'm not convinced that's a real concern. The reason being those two 4BD1s had well over 20,000 hrs when I left the boat. #1 worked hard, high electric loads as well as a hydrualic pump mounted on the front end. #2 just loafed. Usually around 5% - 10% load. Both were fine. In fact #2 seemed to be in better shape having had an easy life.
How old is the genset? Marine age is just as important as hours.

Any chance the valve train became seized or damaged due to a previous back flooding that is now rearing its head? Valve seating issues due to wear, rust or corrosion can indeed lower compression.
Cylinder glazing is real. I spoke to an Annapolis Yanmar/Northern Lights dealer about it. He says he does a nice business in the spring, rebuilding gensets that spent the winter in the Caribbean loafing along 24/7. He pulls the head and pistons, then lightly hones each cylinder to remove the glaze.

Even if the rings are shot (and why they would be after 450 hours is beyond me), an overbore and new pistons should solve it at half the cost of a new genset. Or maybe just a honing and new rings.

Tony Athens, the Cummins guru on recommends the 8 hour at 80% fix. He says it works about 80% of the time.

My first experience with a no start GEN was on the purchase survey of the current boat. I was following the mechanical surveyor progress which came to the GEN. The owner quickly said it will crank but not start and he has his mechanic estimating $1200 repair costs so a running GEN is included in the purchase.

Time for lunch, the mech surveyor said he has his and will continue, so I said start the GEN. We returned to hear the GEN running. It has been running each time since then. No parts, no extra charge. I asked if he used a hammer, he nodded.

Peter you tested the stop solonoid after pulling it and it appeared to work. Did you test it connected to oem wires with someone pressing the stop button with key ON?
No matter you have replaced it and it still does not start.
As the owner was present I did not ask mech to show what he did, and only suspect he tapped on the pump housing to unstick it. WAG, something is stuck in shut off mode from lack of use.
It has started each time since but Note to self, start it on a regular basis.
Did anyone check to see if fuel was actually coming out of the injectors while cranking?
Peter, here is a easy peasy test.

While cranking spray a little starting fluid into the air cleaner

See if the engine fires.

If it fires you have a fuel problem.

if it does not fire the low compression diagnosis might be correct
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I'd pull the head and inspect the gasket, Valves, bores, camshaft.
That is assuming you're getting fuel pressure at the injectors.

The WD40 test is a good one also. Better to use than starting fluid.
Low compression or not, you should be able to start it with heat. I've started some very old, warn engines with terrible compression by heating with a block heater. A pan heater probably won't be hot enough.
Sometimes low compression engines won't start with ether, but will start w/o ether when the block is warm. A block heater would probably need to be on for 3-4 hours.
In the winter some engines in very cold weather with have their rings contract and show very low compression. Somehow getting the engine started with heat, etc., and getting it under a load for a few hours will reset the rings.
Low compression or not, you should be able to start it with heat. I've started some very old, warn engines with terrible compression by heating with a block heater. A pan heater probably won't be hot enough.
Sometimes low compression engines won't start with ether, but will start w/o ether when the block is warm. A block heater would probably need to be on for 3-4 hours.
In the winter some engines in very cold weather with have their rings contract and show very low compression. Somehow getting the engine started with heat, etc., and getting it under a load for a few hours will reset the rings.
I wonder if that explains why my GEN is heated from the starboard engine. The setup does not look after factory install. Kepp the block warm, great tip.
My westerbeke died exactly the same way. Too many parts were No Longer Available to do a viable rebuild. I tore the engine down after putting in a new Phasor gen. The piston rings were fused to the pistons with carbon and one wrist pin was nearly seized. Sold it for parts. What I learned was how important proper loading was. The previous owner started the generator when he left the dock and only shut it down when he came back using a few amps for the refrigerator.
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Couple of things:

On most generators there is a circuit that bypasses the shutdown circuit for low oil pressure or high coolant temperature (some times other parameters are included). When the circuit senses low oil pressure it makes the stop solenoid turn the generator off. Because there's no oil pressure when you try to start the generator, there is a 30 second or so time delay that bypasses the shutdown circuit. Maybe there's a problem with the bypass circuit and it's also shutting down an electric lift pump.

On my generator, I can disconnect the positive lead on the electric lift pump and bring a wire from the positive side of the battery to run the lift pump. I do this when changing the separator element and the fuel filter. The added benefit is once the fuel has filled the separator, filter, and through the injector pump, I can hear the fuel splashing as it falls back into the fuel tank.

My recommendation is to provide power to the electric lift pump (if so equipped), verify fuel flow, and then try starting the generator. If it runs, you still have to address the initial start time delay circuit.

200psi on all cylinders?

I can't imagine that they all got equally old overnight by enough to make the engine go from starting and running well to not starting at all. Not unless you were feeding blasting media directly into the air intake. Nevermind with just 450hrs. I'm just not that imaginative.

If you found uneven compression, I could believe a cylinder or even two went bad. Maybe the head gasket failed between two cylinders. But three for three? Seems unlikely. Not unless there was an overheating episode or water ingestion.

If it were already high hours and huffing black smoke, I could more easily believe they just timed out. But I just am having a hard time with this being the most likely case given the fact picture.

Both starting the engine and performing a compression test rely upon the starter reaching some threshold rpm. A compression test will show low on all cylinders if the compression cycle isn't fast enough as compared to the natural leak rate.

Occam's Razor says to start by suspecting the starter. Check the batteries the wiring, the connections, and then take the starter to an electrical shop and get it tested for free. A failure of the starter to turn the engine fast enough would explain both the sudden failure to start and the suddenly low-but-even compression test result.

The next thing I'd do would be to test the cooling system for leaks, especially the head gasket:


I have this one, but it shows unavailable:

Finally, I'd do, or get done, a leakdown test. Unlike a compression test, it uses an external, independent compressor or pressurized tank of gas to pressurize the cylinders. This will isolate a bad engine, e.g. leaking rings, bad cylinders, etc, from a problem generating the required test conditions for a compression test, e.g. starter, battery, battery cables, etc.

Lastly I'd triple check fuel supply and preheat. Maybe its been low compression for years and, even if imperfect, its a red herring. That leaves fuel and air on the list...

Happy hunting!
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Would there be a compression release for starting which needs x rpm before it can start? The question of whether the battery was strong enough to spin fast enough made me think of this.
Thanks for the ideas- I’ll get on it and report back.
I probably don't need to write gets written a lot...but for completeness...don't forget to check the negative conductor and related current-carrying wires, connectors, interfaces, etc. The ground can (steal the) bite!
Sounds like they missed a few steps in their troubleshooting before condemning the entire dang engine. And each subsequent diagnosis is not great. I even question the compression test

Somewhere in the manual or via tech support they should have the target RPM for start (found in the manual- 250 rpm min). A cheap optical tach and tape will verify. That would rule out/in starter and batt issues.

Leakdown test is the very next step after cranking compression is suspect. That will tell you if it is bypassing rings, intake valve, exhaust valve, head gasket.

A borescope in the cylinders may be in order.

I would also pull the glow plugs and hang them and test that they glow bright red before and during cranking. I assume its now cold where you are. Some gens are really hard to start or impossible to start without glow plugs operating. I just found the manual and it states that this engine needs glow plugs to start in cold weather If the glow plugs havent been confirmed to operate during preheat/prime as well as during start I would do that first.
Then I would hang the injectors and check for good spay pattern.
Glow plugs?

Does it have glow plugs? Mine I had to grind on it for 5 minutes to get her started (I just bought the boat). The relay and glow plugs were bad. It then took about a minute on passing the relay but testing the glow plugs they are bad too. Good luck. My gen has 5000 hours on it.
If Hatton said the stop solenoid was bad and it wasn't, then declared that the injection pump was faulty and it wasn't, I would NOT believe their compression tests. I would give a shot of starting fluid just to see what happens, would also crack the feed lines to the injectors to make sure there was fuel (no bubbles).

Make sure to check the electric lift pump. I found mine quit working and gen would not start. Replaced with 35.00 pump off amazon and now it starts right away with no pre heat. I think my lift pump had a hole in the diaphragm for years as it was always hard starting until it wouldn't go anymore. I took the old one apart and the rubber diaphragm was toast. That engine you have is good for 20,000 + hrs. CarBole 12D Micro Electric Diesel Fuel Pump Universal 5/16 inch Inlet and Outlet 12V 1-2A 35GPH 4-7 PSI
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Hi Pau Hana
Did you ever solve this genset problem?
My two cents would be that since it happened suddenly it is unlikely to be a mechanical issue, rather some kind of electrical connection. I would also start with this avenue of troubleshooting since it is much easier to get to than all the mechanical sources of trouble.

If you could get a manual for your generator, you might find it tells you what is the start-up sequence regarding sensors and sensor overrides, what is powered and what is not powered in terms of solenoids and pumps.

My experience after many years of these things is that one of the sensors has gone bad

Good luck.

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