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Old 14-01-2015, 11:08   #1
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Compression Issues 3QM30(f)

Hey Cruisers,

I noticed as I came online to type this post that there is another thread going right now about a GM series and bad compression in one cylinder. I dont mean to clutter the board with repetitive posts, but my issue is a bit different. I know this is long, but hopefully I can save us some time with our troubleshooting.

Brief history on the motor: Installed in a 1970 Morgan in 1980 by an active sailor who regularly maintained and used the engine for a solid thirty years. By 2010-2012 he didnt use it as much and I bought it from him in 2012. I've used it regularly, but never running more than a few hours per week on average. Over the last two months, I've been running this engine like mad on my trip through the ICW, probably around 200+ hours over that time period. Oil changes regularly, generally well maintained.

Symptoms: About a month ago we noticed the engine wasn't starting very well when cold, and the problem was getting worse over the next week of running it. We first thought air in the fuel lines, so we bled up to the cylinders with success each of the next few days, allowing us to get the hell out of Morgan City and further East where we thought we'd find more help. We noted a LOT of white smoke from the exhaust when the engine finally did start, and a slight sheen in the water. No black, dark gray, or blue smoke. We could hear one cylinder taking an additional 2 seconds or so to crank up to speed.

Through a couple of weeks of troubleshooting, we three rookies figured a leak in the fuel injector pump, then we figured a leak in the fuel filter, then maybe a buggered injector release valve thats allowing air in somehow. Another train of thought was maybe backwashing from the exhaust mixing elbow from running the starter so much during troubleshooting, but we really doubt it given how well she seems to run when shes going. Still another train of thought was the fuel may be flooding a cylinder (lots of white smoke) with a faulty pump or injector valve, preventing even compression and making it hard to start the motor.

* We tried decompressing one cylinder at a time and found the middle cylinder to be doing most/all of the work starting the motor. #2 works very well, but #1 and #3 are not getting compression on their own well at all.

How we've tried to fix the problem: Following the suggestions of many Yanmar mechanics, and with the help of Charlie at Bell Marine in Pensacola (this guy knows everything about Yanmars and has access to virtually all parts old and new, I very strongly recommend him), we switched the injector valves out. No luck.

* During this process, we very slightly opened up the fuel lines at the injector valves to check fuel pressure, and the aftmost cylinder is shooting more fuel that we'd like, the other two are pushing consistent drips. Also, we ran with the oil cap off for a bit to check for any smoke in the top cover. Nothing, she looked great.

Our strategy today: We're going to pull the injectors again and check the gaskets (we reused some since they didnt come out with the injector and we didn't see any damage), re-check all the valve rods and springs under the top cover for bends (none of them are sticking), and then move on to checking the fuel pump.

I really hope its a bad gasket, I expect its going to be a faulty fuel pump, and I'm terrified to think it could be some kind of hydrolock thats ruined the bottom end of the engine.

If ya made it this far reading, thanks very much for your time! Do you by chance have any suggestions or input to give?
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Old 14-01-2015, 11:26   #2
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Re: Compression Issues 3QM30(f)

How often have you had the injectors serviced and when was the last time? What is the compression on the 3 cylinders? Have you checked the spray pattern on the injectors?
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Old 14-01-2015, 11:31   #3
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Re: Compression Issues 3QM30(f)

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Originally Posted by DeepFrz View Post
How often have you had the injectors serviced and when was the last time? What is the compression on the 3 cylinders? Have you checked the spray pattern on the injectors?
Hey DeepFrz thanks for chipping in!

I havent had the injectors serviced since I've owned it, we haven't tested compression yet but are almost certain compression is low (but not 0 psi) in #1 and #3, and the Yanmar tech is going to test the spray pattern today on the injectors.

We're pretty sure the problem isn't with injectors since the problem continued after the new injectors were put in.
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Old 14-01-2015, 13:10   #4
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Re: Compression Issues 3QM30(f)

I'll point you to my little engine rebuild saga. I was Bored so Pulled the Head on my Yanmar

Mine was a 3gm, but the 3qm is similar. Better as it has sleeves.
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Old 14-01-2015, 14:16   #5
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Re: Compression Issues 3QM30(f)

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Originally Posted by sailorchic34 View Post
I'll point you to my little engine rebuild saga. I was Bored so Pulled the Head on my Yanmar

Mine was a 3gm, but the 3qm is similar. Better as it has sleeves.
Thanks for the link, Sailorchic. It looks like you really got into it with your engine, but you certainly proved capable at least from what I've read so far. I'm reeeeally hoping I dont have to go as far as you did. I'm [hopefully] likely looking at a new fuel pump as of yet, but the more I can read about other experiences the better off I'll be.
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Old 14-01-2015, 14:32   #6
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Re: Compression Issues 3QM30(f)

White smoke generally indicates water--a blown head gasket, perhaps.
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Old 14-01-2015, 18:07   #7
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Re: Compression Issues 3QM30(f)

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Originally Posted by Terra Nova View Post
White smoke generally indicates water--a blown head gasket, perhaps.

Or raw, unburned fuel, anytime I start a tractor or backhoe in the winter cold they start out one cylinder hitting after cranking for several seconds, lots of white smoke and then the other cylinders hitting, smoke goes away pretty quick and things warm up


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Old 14-01-2015, 18:20   #8
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Re: Compression Issues 3QM30(f)

I'd check compression first. If you have an issue here then address that first before dealing with the fuel system.

Messing about with diesel injectors and reusing gaskets is a red flag. Diesels need precise fuel metering. This isn't something you can faff about with. When in doubt get the pump tested properly and get the injectors bench tested. Once they're good give them clean fuel and they'll be fine.

Make sure you don't have fuel issues on the suction side of the lift pump or filter issues. Is the lift pump ok.

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Old 15-01-2015, 11:31   #9
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Re: Compression Issues 3QM30(f)

We checked the injectors while connected to the engine. They're 3 brand new injectors and all three looked to be shooting more of a straight stream than a wide cone of atomized fuel. According to the book this is likely a result of low fuel pressure. We're not sure this is whats causing the issue, but is it possible? Brand new injectors, all showing the same low-pressure symptoms.

Is it possible that the fuel pump could be pushing just short of ideal pressure, preventing combustion in some cylinders? Then, when the engine turns over again, there is now twice as much not-atomiozed fuel in these cylinders, again preventing combustion because its over filled. Each time the engine turns over its pumping more liquid fuel into the cylinders...?

For whatever reason, #2 is always able to start. When #2 heats up #1 and #3 enough, they kick in as well, which is when all the white smoke and sheen of diesel fuel on the water comes out.

I'm pretty sure we're not burning water or oil, just excess fuel. We're getting the injectors tested today, and we're going to check compression on each cylinder as well. I expect compression to be a bit low, but not crazy low. If thats the case, we'll likely attack the fuel system at the lift pump and the injector pump.

I'll update later today. Thanks everyone for your input thus far!

EDIT: It occurred to me that about a month or so ago, around when this problem was just starting and we were bleeding fuel lines since we thought we had air in them, we saw a "squirt" of fuel shoot out of the side of the injector pump. Maybe theres a busted hose or connection....? would that cause a leak, low pressure, and therefore poor starting?
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Old 15-01-2015, 12:26   #10
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Re: Compression Issues 3QM30(f)

Your pump may need re-building, if your injectors are new, and if they are the correct one, odds of getting three new, bad injectors?
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Old 15-01-2015, 13:18   #11
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Re: Compression Issues 3QM30(f)

It's easy to check fuel pressure.
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Old 16-01-2015, 21:36   #12
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Re: Compression Issues 3QM30(f)

Today was a bummer of a day.

After getting the injectors checked out they were all fine. We re-checked the fuel pump and its fine. When we went to install the injectors we found coolant in the forward injector that had seeped into the cylinder while the engine sat the last 36 hours or so. We've never seen this before, but its likely that we'd never had the injectors pulled that long after the engine had sat, so whatever coolant had leaked into #3 was probably shot out when we test started it before pulling injectors. Its pulling in very little coolant, but seeing any leak at all means we have some very serious issues. Possibly a cracked head on the forward (#3) cylinder.

We also noticed a knock in the rear (#1) cylinder. We think that could be some slack between the rod and the piston head, but we're not sure.

Eliminating compression from the #2 cylinder kills the engine, which means the middle cylinder is doing most of the work and #1 and #3 arent even getting enough compression to continue to run alone even after running for a while.

I fear the engine might be too far gone to make it worth keeping. I hate to say it, but I'm now forced to embrace the reality that I may have to repower the boat within the year. I don't know how long we can go on this engine before things get too bad to run it.
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Old 16-01-2015, 21:44   #13
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Re: Compression Issues 3QM30(f)

That's about what I figured from the white smoke. Blown head gasket, at least.
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Old 16-01-2015, 21:50   #14
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Re: Compression Issues 3QM30(f)

Sounds like a quick removal of the head is now indicated. If there is no obvious gasket issue, then a visual check for cracks in the head in the region of the offending cylinder, followed if necessary with a trip to the shop for a pressure check/cleanup etc.

Continuing to run it at this stage is not going to help you in the long run... could lead to further expensive damage. Time to face the facts, mate.... aarrghhhh!

Sympathy forwarded!

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Old 21-01-2015, 13:57   #15
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Re: Compression Issues 3QM30(f)

I'm the guy who started another thread with the aforementioned compression issue on a 3GM.

Sorry to hear about your woes pal, we have a lot of the same issues and it leads me to think perhaps much of what I am doing is wasted cash that could be put toward a new engine.

Nevertheless, what I have learned in the past 6 months about marine diesel engines and what makes them run I feel is priceless as it is a fundamental aspect of my hobby.

Like Jim Cate said, pull the head off and have a look at it, even if its just for experience building. Maybe, just maybe, you can get away with a new head gasket for a fraction of the price of a new engine.

Best of luck
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