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Discussion Starter #1
I need some help here. While I have a fairly good shade tree mechanic experience with gasoline engines, this is my first diesel engine.

My starting problem has been getting progressively worst over the years, to the point where now I have to give it full throttle to start the engine. In an effort to resolve this problem the head was rebuilt by a reputable machine shop, and the injectors were rebuilt by my local boat yard.

To start the engine I have to crank it for a while and give it full throttle. When it does start it seems to start on one cylinder, while keeping it in the higher RPM range so it does not stall, after a while the second cylinder kicks in.

While cranking at startup I get occasional kick back. During the start up and until it warms up a little there is a lot of suttee black smoke. During startup and after the engine fully warms up under way there is what the mechanic tells me is a fuel knock. When under way I am able to reach full RPM's.

Now I am being told that the compression is low, and that it might be as simple as frozen piston rings.

At this pint my main question is, if the compression is low why would I be getting fuel knock. As I understand it fuel knock and kick back is a result of early combustion of fuel, and it seems to me that if you had low compression the fuel would ignite later rather than early.

Any help is appreciated.
 

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I had the same type problem on my 1GM10, the single cylinder model of the 2GM and it was the injector timing. also I don't rebuild the injectors as they are only $100 each and the cost to rebuild is $125. did your mechanic set the timing to 15 or 25 degrees yours should be 15 and some mechanics don't know that there is a difference in the models of the 2GM series engines
low compression can be valve setting. make sure that the two end valve rockers are held in towards the center of the engine as they will slip outward during setting with the valve cover off and the valve clearance will be to tight when you reinstall the valve cover.
 

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When you push the throttle to full open, you are both introducing more air to accommodate ignition and flooding the cylinder at the same time. The chugging you are referring to as starting on one cylinder sounds like a symptom of poor atomization of the fuel/air mixture. That's how a flooded engine runs at first.

As you said in your other thread, you had the injectors rebuilt, but haven't clarified what that means. All signals are to a fuel/air problem and injectors are usually at the heart of that. They simply wear out. Other causes could be a blockage or poor fuel pump pressure, but less likely. Although, some get ridiculous with the fuel filters they use and assume that lower microns are always better. Not always true, as your system may clog too fast or overwhelm your pump. Have you checked them? What microns do you use? Also, as I mentioned in your other thread, the rebuilt injectors may have been reinstalled incorrectly, with the wrong seats, so the spray pattern would be affected.

Personally, I've had smoking issues and oil burn from low compression, but until its very low, I've not noticed this kind of starting trouble.
 

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I think OB and Minne are on the right track.. while 350 compression may be on the low side I don't think it's low enough to make starting problematic with good fuel delivery. And that means timing and proper atomization.

If you're cranking for excessive time periods try to remember to leave your RW intake closed until the engine catches. Flooding the exhaust system with RWC is never a good thing.

Having to use wide open throttle during starting seems to be SOP for some of these older Yanmars..
 

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Discussion Starter #5
did your mechanic set the timing to 15 or 25 degrees yours should be 15 and some mechanics don't know that there is a difference in the models of the 2GM series engines
low compression can be valve setting. make sure that the two end valve rockers are held in towards the center of the engine as they will slip outward during setting with the valve cover off and the valve clearance will be to tight when you reinstall the valve cover.
As you said in your other thread, you had the injectors rebuilt, but haven't clarified what that means. All signals are to a fuel/air problem and injectors are usually at the heart of that. They simply wear out. Other causes could be a blockage or poor fuel pump pressure, but less likely. Although, some get ridiculous with the fuel filters they use and assume that lower microns are always better. Not always true, as your system may clog too fast or overwhelm your pump. Have you checked them? What microns do you use? Also, as I mentioned in your other thread, the rebuilt injectors may have been reinstalled incorrectly, with the wrong seats, so the spray pattern would be affected.
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There were 3 different mechanics who worked on the engine over the years. Each time I ask around and try to find someone who really knows what they are doing. The last one (No. 4) I had look at it and took the compression, he works exclusively on diesels. But, he said he works on larger engines and he did not sound that familiar with this engine, he also said the timing is fixed at the factory. The injectors were actually rebuilt 4 seasons ago and again this last season. Unfortunately I don't know what that means since i relied on others. No improvements either time. This is why I have to take matters into my own hands. There are to meny people out there who call themselves mechanicks.

The fuel filters I have always changed myself. There is a water separator mounted up stream of the engine, and the filter on the engine. Even though I don't have the numbers on hand I don't believe that is the problem since I get the same numbers every year to replace them, and the engine used to run better.

I will check the valve adjustments, mixing tube, and I will get a brand new set of injectors and seats, worst case scenario I end up with a spare set. Also, it has been suggested in my other thread to change out all the fuel components.
The Fuel Feed Pomp works fine. Personally, I am leaning towards the Fuel Injection Pump or timing.

I don't know how to trouble shoot the Injection Pump. The Yanmar manual is not very helpful when it comes to trouble shooting.
 

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Full throttle at start-up is normal for my Volvo diesel motor.
Remember though guys, there is no throttle (per se) in a diesel motor in contrast to the throttle gates of a gasoline engine.
For a diesel, full throttle just helps enrich the first few firing strokes.... it squirts more fuel in.
Throttle back the moment it starts.
 

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Am I correct in thinking that the Yanmar doesn't have glow plugs? I'd expect this to result in difficult starting and having to use full throttle to start. Can't understand why they thought it would be OK to not install them.
 

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Am I correct in thinking that the Yanmar doesn't have glow plugs? I'd expect this to result in difficult starting and having to use full throttle to start. Can't understand why they thought it would be OK to not install them.
I have no glow plugs on my Volvo and it starts right up, in idle, every time. Knock on wood! I had to move it a couple of years back on a 30 deg day in March and it fired up normally after sitting on the hard for months.

The bloody turbo, however, gives me fits.
 

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Am I correct in thinking that the Yanmar doesn't have glow plugs? I'd expect this to result in difficult starting and having to use full throttle to start. Can't understand why they thought it would be OK to not install them.
I have the same motor as the OP. I always do a cold start at 3/4 throttle, throttling back to idle immediately after start, as directed in the manual. It's over 20 years old, does not have glow plugs, and has never had a starting problem (in the moderate SF Bay Area climate). Kicks on the first crank every time! Once warm, it starts immediately from idle position.
Sounds like a good Yanmar mechanic is in order for the OP. If he is in the Bay Area, List Marine will sort it out in short order. I'll bet they will also tell him to cruise at 3000 RPM when it is running properly. Makes for a happy 2GM20!
 

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Discussion Starter #10
Am I correct in thinking that the Yanmar doesn't have glow plugs? I'd expect this to result in difficult starting and having to use full throttle to start. Can't understand why they thought it would be OK to not install them.
Agreed, it does not have glow plugs, and it probably should, it would help if it did. But, about 8 years ago it used to start with almost no throttle. Whatever is going on is not normal.
 

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Discussion Starter #11
I have the same motor as the OP. I always do a cold start at 3/4 throttle, throttling back to idle immediately after start, as directed in the manual. It's over 20 years old, does not have glow plugs, and has never had a starting problem (in the moderate SF Bay Area climate). Kicks on the first crank every time! Once warm, it starts immediately from idle position.
Sounds like a good Yanmar mechanic is in order for the OP. If he is in the Bay Area, List Marine will sort it out in short order. I'll bet they will also tell him to cruise at 3000 RPM when it is running properly. Makes for a happy 2GM20!
Opposite end of the country. I am in NY Long Island Peconic Bays area, pretty much the same climate. My engine at this point stalls after start if I pill back to idle immediately, I have to keep it in the 2000 to 2500 revs until it smoothes out. And, when warm when its running it sounds like there is a man with a hammer in the engine (mechanics called this fuel knock).
 

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Discussion Starter #12
I think OB and Minne are on the right track.. while 350 compression may be on the low side I don't think it's low enough to make starting problematic with good fuel delivery. And that means timing and proper atomization.

If you're cranking for excessive time periods try to remember to leave your RW intake closed until the engine catches. Flooding the exhaust system with RWC is never a good thing.

Having to use wide open throttle during starting seems to be SOP for some of these older Yanmars..
Ok, I am listening, does this apply to fresh water culled engines?
 

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Discussion Starter #13
I looked into compression, and I see that the manual says the Compression Ratio should be at 23, multiplied by atmospheric pressure 14.7, this equals 338 PSI. Surprisingly 350 is above that. The Mechanic did say he took the compression with a warm engine. He also said that the rings might be stuck/frozen, this might make a difference with a cold start. It looks like he might be on the right track.
 

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Ok, I am listening, does this apply to fresh water cooled engines?
Yes.. in either case the RW is pumped through the engine (RWC) or a heat exchanger(FWC) and then is injected into the exhaust system to keep the noise level down and to cool the exhaust run out to the transom.

The water is driven out of the exhaust system by the running engine's exhuast gases. If the engine never catches, the rotating RWpump will fill the muffler, eventually possibly backing up into the exhaust manifold where it will find an open exhaust valve and run back into that cylinder. This can cause 'hydrolocking', where the engine won't turn because it can't compress the liquid pocket in the cylinder.

I'm still leaning toward a faulty injector, certainly it's the top candidate for the 'hammer' sound while running.
 

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Cold start procedures for a 3GM30F(an indirect injection diesel) is similar..full throttle as described in the workshop manual which retards timing. Decrease throttle after diesel starts.

DO NOT use any starting type of sprays/fluids as this procedure may result in bent con rods. I personally know what bent rods look like...:eek:
 

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Yes.. in either case the RW is pumped through the engine (RWC) or a heat exchanger(FWC) and then is injected into the exhaust system to keep the noise level down and to cool the exhaust run out to the transom.

The water is driven out of the exhaust system by the running engine's exhuast gases. If the engine never catches, the rotating RWpump will fill the muffler, eventually possibly backing up into the exhaust manifold where it will find an open exhaust valve and run back into that cylinder. This can cause 'hydrolocking', where the engine won't turn because it can't compress the liquid pocket in the cylinder.

I'm still leaning toward a faulty injector, certainly it's the top candidate for the 'hammer' sound while running.
You just gave an excellent reason why I need to fix the starting issue. Water in the head at the valves and hydrolocking can result in some costly damage, aside from getting stuck somewhere and losing a good part of the season. Thanks, for the input.

I agree about the injectors. The way I understand it the injectors are the only thing that could be allowing too much fuel to get in the engine and cause fuel knock. If the Injection pup was failing that would result in not enough fuel. Are my assumptions right?
 

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I agree about the injectors. The way I understand it the injectors are the only thing that could be allowing too much fuel to get in the engine and cause fuel knock. If the Injection pup was failing that would result in not enough fuel. Are my assumptions right?
That's been my experience.

On our last rebuild I ordered a full set of 'reconditioned' injectors. During the break-in period we got some fuel knock that scared the H out of me because it sounded like metal-to-metal contact.. gladly discovered eventually that one of the 'new' injectors was breaking over at under 500 psi = wet fuel = serious knock. Replaced injector and off to the races.
 

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Discussion Starter #18
That's been my experience.

On our last rebuild I ordered a full set of 'reconditioned' injectors. During the break-in period we got some fuel knock that scared the H out of me because it sounded like metal-to-metal contact.. gladly discovered eventually that one of the 'new' injectors was breaking over at under 500 psi = wet fuel = serious knock. Replaced injector and off to the races.
That is exactly what my knock sounds like right now.
You and a number of other people are saying the same thing about rebuilt injectors. Surprising that anyone even bothers with them.
 

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Discussion Starter #19 (Edited)
Cold start procedures for a 3GM30F(an indirect injection diesel) is similar..full throttle as described in the workshop manual which retards timing. Decrease throttle after diesel starts.

DO NOT use any starting type of sprays/fluids as this procedure may result in bent con rods. I personally know what bent rods look like...:eek:
If your engine was built after 1997 that might explain the difference. My manual covers the 1, 2 & 3GM models.
Normal start positing is at medium speed.
The exception is starting in cold weather the throttle should be in high speed with the decompression handle in the decompression position, start cranking and push the lever to the compression position, after it starts pull back to medium speed. There seems to be a conflict because there is a "caution" which states to pull back to idle immediately when the engine is started at high speed. We all know you should not rev a cold engine any more than necessary . The injection timing being delayed at high speed is also there.

I would actually be happy if the engine started right away on a 80 degree day, and came right back to idle without stalling.
 

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Discussion Starter #20
Ran some tests, cranking and playing with the decompression lever with a cold engine does not feel like it changes anything, it only feels like the compression builds up after the engine warms up. This just might be explaining the hard start problem.
 
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