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Old 12-05-2020, 10:24   #1
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Yanmar 2QM20 running issues

Hi all
I am looking for some help with troubleshooting an issue with my Yanmar.

Engine ran fine until I was out cruising last summer, and then it had trouble starting and running. After spending hours trouble shooting it to no avail, and then limping home it sat for a month before I could begin troubleshooting and then discovered that it wouldn't start with out the throttle at full. It currently only starts and runs with the throttle wide open. Lots of white smoke.

I started with the fuel lines and had found no air leaks, went to my elbow and cleaned, then checked my injectors, one came out and i was able to clean it but the other I could not remove, various attempts later lead to the decision of removing the head, and I discovered some serious corrosion on the top of the combustion chamber and around the exhaust valve.
I have replaced the head and both injectors, added a 12v fuel pump, replaced/inspected all banjo bolts and washers, cleaned the exhaust manifold
and elbow. Lift pump works fine, Valve lash has been set and reset, I checked the injection timing last year, but I want to recheck it.

I am a decent mechanic, but more familiar with larger engines, and this problem is very much stumping me. One suggestion I had from a dockmate was to check the inlet screen on the injection pump. I have not done this yet.

Thoughts? Questions?
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Old 12-05-2020, 14:08   #2
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Re: Yanmar 2QM20 running issues

Wecome aboard the CF Island cruiser Have you done a compression test? What caused the salt water to get in the combustion chamber?
White smoke is unburnt diesel often caused by lack of compression. You may have broken or stuck rings.
I assume you did a valve grind. Your injection timing shouldnt change but doesn't hurt to check.
Needing full throttle to start is often a sign of low compression as well. This is general diesel info.
There is a few 2QM20 owners around on CF so you may get engine specific info. Wotname has a workshop manual or check the CF library.
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Old 12-05-2020, 17:40   #3
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Re: Yanmar 2QM20 running issues

Welcome aboard CF, Islandcruiser.

Sorry to hear about your 2QM20 troubles and I must confess they are my favourite engine

Some random thoughts about your problem.

The timing shouldn't change unless you have had the injector pump serviced/overhauled provided you haven't changed the shims when removing / refitted the injector pump.

I presume the replacement head / injectors / exhaust manifold were serviceable when fitted so they can be excluded from the fault finding process (for the moment).

You only need fuel, air and compression to start and run a diesel engine.

Air is usually not a problem unless there is a restriction in the exhaust system (unlikely given you have cleaned the elbow and manifold) or a blockage in the air cleaner (easily checked). For a test, you could try starting the engine with the exhaust disconnected after the elbow.

While fuel problems are common, you have given a lot of care to the fuel system so that makes it unlikely in this instance. A definitive test is to pull an injector leaving it connected to the injector pump and observe the spray pattern while turning the engine over by the hand crank or starter motor. Use caution and make sure the spray is directed well away from all parts of your body.

That leaves compression and perhaps this is where the problem lies. Maybe the rings have gummed up and are not seating against the cylinder wall. While a compression test is the best method, a quick and dirty test is to remove the head , rotate the pistons until they are half way between TDC and BDC. Fill with diesel and observe how fast the diesel drains into the sump. It should take hours, not minutes. Of course, you need to drain the sump afterwards!

If the rings aren't sealing well, try flushing diesel though them for a few days while moving the pistons up and down a bit. This sometimes will free them.

That should be enough to start with
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Old 12-05-2020, 17:47   #4
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Re: Yanmar 2QM20 running issues

FWIW, for some light reading, you may like to look at this thread about my seriously challenged 2QM20.

https://www.cruisersforum.com/forums...20-233366.html
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Old 12-05-2020, 18:09   #5
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Re: Yanmar 2QM20 running issues

I forgot to add...

You haven't mentioned anything about the electrical aspects - is the starter motor still spinning the engine over rapidly or has it slowed down in anyway???

If it is not turning the engine over fast enough, you will not get a start although it won't have any effect how well it runs after starting.

A quick test is to decompress the engine while turning it over with the starter motor. While keeping the starter operated, re compress the engine after 2 or 3 seconds. If it starts now, then starter motor is turning too slowly for a regular start.
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Old 17-05-2020, 10:20   #6
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Re: Yanmar 2QM20 running issues

Quote:
Originally Posted by Compass790 View Post
Wecome aboard the CF Island cruiser Have you done a compression test? What caused the salt water to get in the combustion chamber?
White smoke is unburnt diesel often caused by lack of compression. You may have broken or stuck rings.
I assume you did a valve grind. Your injection timing shouldnt change but doesn't hurt to check.
Needing full throttle to start is often a sign of low compression as well. This is general diesel info.
There is a few 2QM20 owners around on CF so you may get engine specific info. Wotname has a workshop manual or check the CF library.
Thanks for the replies,
Valves came new with the head pre ground, I should have written before i did a compression test and it was fine in one cylinder and a little low in the other, which I had chalked up into being from the massive pitting in the head on that side. Ive never heard that using full throttle is a sign of having low compression.
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Old 17-05-2020, 10:36   #7
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Re: Yanmar 2QM20 running issues

Quote:
Originally Posted by Wotname View Post
Welcome aboard CF, Islandcruiser.

Sorry to hear about your 2QM20 troubles and I must confess they are my favourite engine

Some random thoughts about your problem.

The timing shouldn't change unless you have had the injector pump serviced/overhauled provided you haven't changed the shims when removing / refitted the injector pump.

I presume the replacement head / injectors / exhaust manifold were serviceable when fitted so they can be excluded from the fault finding process (for the moment).

You only need fuel, air and compression to start and run a diesel engine.

Air is usually not a problem unless there is a restriction in the exhaust system (unlikely given you have cleaned the elbow and manifold) or a blockage in the air cleaner (easily checked). For a test, you could try starting the engine with the exhaust disconnected after the elbow.

While fuel problems are common, you have given a lot of care to the fuel system so that makes it unlikely in this instance. A definitive test is to pull an injector leaving it connected to the injector pump and observe the spray pattern while turning the engine over by the hand crank or starter motor. Use caution and make sure the spray is directed well away from all parts of your body.

That leaves compression and perhaps this is where the problem lies. Maybe the rings have gummed up and are not seating against the cylinder wall. While a compression test is the best method, a quick and dirty test is to remove the head , rotate the pistons until they are half way between TDC and BDC. Fill with diesel and observe how fast the diesel drains into the sump. It should take hours, not minutes. Of course, you need to drain the sump afterwards!

If the rings aren't sealing well, try flushing diesel though them for a few days while moving the pistons up and down a bit. This sometimes will free them.

That should be enough to start with
I have not yet removed and inspected the injection pump, so I don't expect it to have changed.
Replacement head and all bits were fully serviced or brand new.
Exhaust manifold and elbow were fully cleaned.
I could have low compression, I haven't done a test with the new head yet.
A bleed down test is another good idea.
They are brand new injectors so I doubt there's an issue but good idea to check for sure. What I do is use a coffee filter held under the injector, this allows you to visually check the pattern and you don't get any on you.


Quote:
Originally Posted by Wotname View Post
I forgot to add...

You haven't mentioned anything about the electrical aspects - is the starter motor still spinning the engine over rapidly or has it slowed down in anyway???

If it is not turning the engine over fast enough, you will not get a start although it won't have any effect how well it runs after starting.

A quick test is to decompress the engine while turning it over with the starter motor. While keeping the starter operated, re compress the engine after 2 or 3 seconds. If it starts now, then starter motor is turning too slowly for a regular start.
I have a new starter from when I bought the boat a few years ago and the battery sits being charged and has more then enough cranking amps for this engine.

Again the issue is it wont start and stay running with out full throttle and before I changed the head I had thought only one cylinder was actually firing.

Thanks for all the suggestions, I plan to do another compression check and check spray pattern now .

Cheers
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Old 17-05-2020, 19:17   #8
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Re: Yanmar 2QM20 running issues

Sorry I didn't understand your 1st post properly in that I thought you had just removed the head not rebuilt it.
The info that the head was badly pitted is scary & I'd guess you have damaged rings & bore in that cylinder. I'd say it's likely that it's only running on one cylinder. You can test that by loosening the injection pipe nuts at the injector one at a time whilst its going & see if it stops running.
You can do this before a compression or spray pattern test. But yes do those as well.

Using full throttle for a start was necessary in our Yanmar before I put new piston,rings & liner in it, now it starts instantly at idle setting except at near freezing temps. High compression makes for easier starts.
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Old 03-06-2020, 21:48   #9
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Re: Yanmar 2QM20 running issues

Well I finally got down to the boat and did a compression test, and spray pattern.
Spray was good, compression was 200psi on both so I'm happy with that. How ever upon removing the brand new injectors I noticed that one was completely clean while the other had a blackened tip as expected. this would cofirm that only one cylinder was firing. I swapped the injectors to see if one was the issue and then I blew the fuse on the starter and didnt have a spare as I had removed them from the boat along with other things to do some painting. So I will give it another go tomorrow after bleeding the fuel.
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Old 03-06-2020, 22:17   #10
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Re: Yanmar 2QM20 running issues

How did you test the spray pattern? Did you check the pop pressure? Did you pull the injectors and use the engine HP injection pump to test the spray pattern? How fast did the compression come up to 200 psi?
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Old 03-06-2020, 22:24   #11
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Re: Yanmar 2QM20 running issues

If you didn’t use the injection pump to test the injectors it could be the injection pump. Similar to this: https://youtu.be/bHLEnfHkn-k

The yanmar injection pump is similar to the Kubota injection pump. It’s very easy to check as the video above shows.
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Old 03-06-2020, 22:45   #12
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Re: Yanmar 2QM20 running issues

If the pop pressure of one injector is above the injection pump pressure it won’t fire. That’s why I asked if you checked the pop pressures.
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Old 04-06-2020, 00:21   #13
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Re: Yanmar 2QM20 running issues

Quote:
Originally Posted by Islandcruiser View Post
Well I finally got down to the boat and did a compression test, and spray pattern.
Spray was good, compression was 200psi on both so I'm happy with that. How ever upon removing the brand new injectors I noticed that one was completely clean while the other had a blackened tip as expected. this would cofirm that only one cylinder was firing. I swapped the injectors to see if one was the issue and then I blew the fuse on the starter and didnt have a spare as I had removed them from the boat along with other things to do some painting. So I will give it another go tomorrow after bleeding the fuel.
Whilst I don't know what your compression is supposed to be, 200 psi sounds way low to me. The 2QM20 is 20:1 compression ratio. Our YSM8 is 23:1 & it's minimum compression reading is 355 psi. It's actual is 405 so I'd suspect your minimum would be around 300 psi.
Maybe someone who knows the 2QM20 can tell you
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Old 11-06-2020, 08:17   #14
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Re: Yanmar 2QM20 running issues

Well the rough math puts it at 320 with a ratio of 22/1. I have access to a pop tester and use a coffee filter around the nozzle to check for spray. Both injectors were fine. I tried running it after swaping injectors and it still runs the same. Loosened off fuel lines to verify which cylinder wasnt firing and it was the same one. So its a fuel issue for sure and that leaves the injection pump. After getting a quote it will be cheaper for me to buy a new rebuilt one so I have ordered a new pump, shims and lines from https://www.hoyetractor.com/PROD/IP-200.htm

so we shall hope it gets here quick!
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Old 11-06-2020, 15:30   #15
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Re: Yanmar 2QM20 running issues

The price is not bad for the injection pump. Think it would be 2x + from Yanmar marine dealer. Still doubt injection pump is your problem but hope I'm wrong for your sake.
I might be a bit confused here but you say that both injectors were spraying? Do you mean they both sprayed on each line or on 1 line only?
If you had good filtration & no water getting in the fuel it's unusual to have injection pump failure.
You say you cleaned elbow but you don't say how the salt water got into the cylinder?
the elbow could be clean & leaking still.
Please post result back after you try new inj. pump
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