3GM30F Service Issue

[jssailem]

That sounds eerily familiar. I think in my case the engine is tight and needs some hours of run time. But I’m also going to try and adjust the timing a wee bit. Thinking the hi pressure pump is a hair advanced putting too much fuel into the injectors/cylinders so I’m not getting full combustion at the start. Once running it may be a bit rich but that appears to be ok. I’ve not yet enough time to check fuel consumption. I’m not yet ready to try and put an exhaust sensor into the pipe to measure the exhaust.

 

[Mark Maulden]

to me, this looks like a leaky injector(s)..You shut the engine down and fuel keeps dripping into the cylinder causing a hard cold start. It immediately starts after shutdown as it hasn’t had time to drip drip drip…I had this issue last summer on my newish Beta. (400) hrs. It was starting a bit hard and had white smoke with 10 sec of glow plugs. Normally need 4-5 seconds. Found nothing wrong with the fuel system. On a whim, I pulled the injectors and took them to Northland. They actually said they were fine, however after installation, the engines fires off immediately hot and cold. No smoke. So they evidently inadvertently fixed something during the injectors disassembly/reassembly. And to this day, with a cold start, I can’t push the start button fast enough and its running.

 

[skunther]

The service manager mentioned that the injector pump may have been previously modified by another shop to order to adapt it to the low compression in the cylinders and make the them perform better. He said the rebuild was to spec, and any modifications to the pump would have been lost, possibly explaining why it now starts hard.

Has anyone heard of such a scenario? Does it sound reasonable?

 

[Davidasailor26]

I don’t know enough about fuel pumps to say for sure, but in years of reading forum posts I’ve never seen “adjust the lift pump” as a suggested fix for low compression.

 

[skunther]

I meant injector pump, not lift pump. Sorry, there doesn’t seem to be a way for me to edit the post to correct it.

 

[Davidasailor26]

I meant injector pump, not lift pump. Sorry, there doesn’t seem to be a way for me to edit the post to correct it.

I thought you might’ve. Same concern though - I’ve never seen that as a suggested mitigation for low compression. Maybe it really is and I’ve just never seen it written though.

 

[jssailem]

I would think if the lift pump is weak then you could get fuel starvation at the injector pump. This more likely would kill the engine in the same way a clogged filter kills the engine.

 

[skunther]

I would think if the lift pump is weak then you could get fuel starvation at the injector pump. This more likely would kill the engine in the same way a clogged filter kills the engine.

The engine runs fine once started. The only issue is starting.

 

[dLj]

Just an observation: I'm surprised your engine even runs at 160 to 170 psi compression levels. Those are gasoline engine compression numbers. Diesel engines are typically around the 300 psi compression level. I think the Yanmar 3GM30 should be in the 320 psi region. Now if that was 260 to 270, I would think you might have a case to continue in this quest. But at those compression numbers I think you need a ring job and possibly valves.

dj

 

[Mark Maulden]

Pull the injectors or glow plugs and put a squirt of 40 wt oil in. Replace injectors or glow plugs and see if it fires off..if it does, it would tell you rings are responsible for low compression.

 

[skunther]

I would think if the lift pump is weak then you could get fuel starvation at the injector pump. This more likely would kill the engine in the same way a clogged filter kills the engine.

Wouldn’t that kill the engine when warmed up and idling/cruising too? The engine seems to perform fine once it finally starts…

 

[jssailem]

Wouldn’t that kill the engine when warmed up and idling/cruising too?

Yes. That is why I do not agree that a lift pump is the issue.
Timing is the usual suspect. After you get the engine running the timing being a little off is less of an issue. You may be running. A bit rich. Or Lean which might show up as the engine running hotter than expected. You can test for compression or you can try to tweak the timing. I think you said the color plugs have been serviced. If the timing is not successful then compression could mean new rings are needed. That is not an easy fix.

 

[jssailem]

I think I might be inclined to struggle with the cold starting issue.

 

[skunther]

to me, this looks like a leaky injector(s)..You shut the engine down and fuel keeps dripping into the cylinder causing a hard cold start. It immediately starts after shutdown as it hasn’t had time to drip drip drip…I had this issue last summer on my newish Beta. (400) hrs. It was starting a bit hard and had white smoke with 10 sec of glow plugs. Normally need 4-5 seconds. Found nothing wrong with the fuel system. On a whim, I pulled the injectors and took them to Northland. They actually said they were fine, however after installation, the engines fires off immediately hot and cold. No smoke. So they evidently inadvertently fixed something during the injectors disassembly/reassembly. And to this day, with a cold start, I can’t push the start button fast enough and its running.

Wouldn’t a leaky injector cause black smoke at startup? I’m currently getting a bit of whitish (and slightly blueish) smoke at cold startup.

 

[Mark Maulden]

Wouldn’t a leaky injector cause black smoke at startup? I’m currently getting a bit of whitish (and slightly blueish) smoke at cold startup.

Not necessarily. It’s a quick project for elimination or success..

 

[Scott T-Bird]

I can't tell if @skunther is concerned about low compression or not. If it were me and I learned that the engine has low compression (how low for sure) I would be focused on that issue, not the hard starting. Low compression would seem to me to be the most concerning issue and I would have to start there, before worrying about hard starting. But it seems that perhaps skunther doesn't really believe the shop guys who tell him that compression is low.

If that's the case, then I would get a second opinion from a shop that is unrelated to the first. I would first want to know, without question, if compression is low, and if so, how low and where do I go from there? It sounds to me that the explanations that he has received so far are bogus. If the engine is in good condition, then finding the cure for hard starting should be a simple process by elimination that any competent shop should be able to resolve. Coming up with nebulous explanations such as "if this, then that" sounds like a cover up to me.

 

[dmax]

Low compression is a root cause of hard starting - hard starting is a symptom of low compression.

 

[skunther]

Thanks. I have on YBW received replies that indicate compression is a nebulous thing, and this is why Yanmar doesn’t publish compression specs for this engine. More relevant, they have said, is that the compression be relatively consistent between cylinders, which in my case it is. I hold to the belief that if the engine started well before work was performed, and nothing else changed, then something was done during the work to cause the issue. If the engine started fine before work was performed, with the same compression, then clearly compression is not the issue, no?

The shop has suggested an engine replacement to deal with the compression issue. A rebuild they said is unreliable and costs nearly as much as a replacement. I don’t have an extra $20k lying around, so I am trying to explore other options.

Air leak somewhere in the fuel system seems a common culprit for these types of starting issues. I plan to try priming the system and see if it starts better.

The engine has 2600 hours on it and seems to otherwise run fine. I will do a compression test myself, or maybe better a leak down test down the road if I’m unable to get any traction on the issue with other approaches.

 

[dLj]

Compression specs for that engine can be derived from Yanmar's published data on the engines specs. It is however, a fairly complicated set of formulas requiring actual measurements of you specific engines cylinders, head, gaskets and such. Consistent compression across the cylinders means that you don't have a catastrophic failure in one cylinder such as a broken or burned valve, ring and the like.

One of the problems of stating if your engine is low in compression is that we don't know how they did the test. The actual way they did it can matter. However, basic diesel engine requirements for good starting and performance begin at around 300 psi. Your specific engine brand new should show compression between about 390 psi and 490 psi. Of course those numbers are based on running the test correctly. Those numbers come out of a Yanmar manual for this engine.

160 to 170 psi compression is very low. either they did not do the test correctly or your engine has low compression.

From all you descriptions, my first reaction would be that you may have sticky rings. That the compression ring has stuck compressed and is not providing the proper seating to generate the required compression. This could easily happen as during all of the work you've had done may have allowed those rings to get stuck during the down time of not being run. That would then make it so now the engine will not start due to low compression. I would be tempted to pull the injectors, put a small amount of 30 weight oil in each cylinder, put the injectors back in and see if it starts. The oil will help the rings to seal long enough to start the engine and then running the engine may loosen them up and get them back running.

dj

 

[dmax]

Sure, it may be something else that is causing the hard starting, but those compression numbers are low for a diesel, which uses compression to ignite the fuel. Understanding that is a good approach.