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Old 27-05-2024, 15:19   #1
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Yanmar 3GM30F Hard Starting

After some work performed on the fuel system (rebuilt injector pump and injectors, replaced secondary fuel filter), my 3GM starts only with ether, while previously it would start within 5-7 seconds without fail, and without ether. Now there is some white smoke at startup, but once warm the engine runs well with very little smoke. It also starts right back up if I shut it off after running it for a bit.

Low compression was measured on the cold engine, uniformly low on all 3 cylinders (160, 170, 160). It started fine before the fuel system work though, which leads me to believe that low compression is not the issue.

What could be causing the hard start? I’ve seen different posts on this, but none seem to address these specific symptoms. Three things that seem common issues are:

Injector leak: If an injector is leaking into the cylinder when the engine is off and left idle, causing a hard start, wouldn’t this produce black/grey smoke at startup, not white smoke?

Air leak in system: If there is an air leak into the fuel system via a poorly sealed secondary o-ring or a stripped secondary bleed screw (mine does not have a washer), wouldn’t that result in poor running once warm? Would it result in the white smoke I’m experiencing at startup? Or could it produce my symptoms? I’ve seen some report that replacing the secondary fuel filter addressed their hard start, and I believe their issue was only with starting, not running.

Dirty fuel: If the fuel is dirty, would the engine not run poorly once started? Mine runs well. One user reported that his fuel was dirty, which caused a hard start, but after a bit the engine would warm causing the fuel to flow better.
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Old 27-05-2024, 17:34   #2
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Re: Yanmar 3GM30F Hard Starting

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Originally Posted by skunther View Post
After some work performed on the fuel system (rebuilt injector pump and injectors, replaced secondary fuel filter), my 3GM starts only with ether, while previously it would start within 5-7 seconds without fail, and without ether. Now there is some white smoke at startup, but once warm the engine runs well with very little smoke. It also starts right back up if I shut it off after running it for a bit.

Low compression was measured on the cold engine, uniformly low on all 3 cylinders (160, 170, 160). It started fine before the fuel system work though, which leads me to believe that low compression is not the issue.
.........

There is a serious disconnect here!

I would be amazed if the engine ever started normally with those compression numbers. They should be (at least) north of 390 psi...

Was the compression test out before or after the fuel system work? While your logic about assuming the fuel system work is the culprit is sound, it is only makes sense if the compression numbers were correct before the work was carried out.

Have the injectors been refitted correctly?

The symptoms kind of indicate low compression but not that low.
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Old 27-05-2024, 17:52   #3
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Re: Yanmar 3GM30F Hard Starting

Those compression pressure numbers are just high enough to allow a hot engine to start and run (but at reduced power).
They are also just high enough to allow a cold engine to start with ether.

Both these conditions match your described fault symptoms but only if the low compression was introduced when the fuel system work was done which could be the injector seals are 'wrong'.

Check the compression test and confirm if the numbers are true.
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Old 27-05-2024, 18:41   #4
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Re: Yanmar 3GM30F Hard Starting

A minor but perhaps important point, was the injection timing carried after refitting the rebuilt injection pump?
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Old 27-05-2024, 19:07   #5
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Re: Yanmar 3GM30F Hard Starting

I used to have to crank my 3GM30 when it was cold, then I learned (here) to crank with wide open throttle. Makes a world of difference -- starts almost instantly when cold.
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Old 28-05-2024, 11:58   #6
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Re: Yanmar 3GM30F Hard Starting

The same shims were used after the IP rebuild, so timing should be the same.
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Old 28-05-2024, 12:00   #7
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Re: Yanmar 3GM30F Hard Starting

Could “wrong” injector seals result in hard cold starting but smooth running and easy re-starts?
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Old 28-05-2024, 14:50   #8
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Re: Yanmar 3GM30F Hard Starting

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The same shims were used after the IP rebuild, so timing should be the same.
Nope, it’s a leap of faith to assume that every pump tech will set up the pump in precisely the same way and that your injector pump cam is totally unworn. 5-7 seconds of cranking would be of concern to me (unless its winter and you’re in Dutch Harbour). Yes , the wrong packings under the injector will cause problems , too thin or missing not so much but too thick or accidentally adding a second washer lifts the injector to a point where the nozzle spray impinges on the precom chamber walls in a way not intended by the manufacturer. This happens more often and with damaging results on direct injection engines but indirect injection is far more tolerant. Is there any smoke? Either at startup or running? Any “blow by”?
I’d be adjusting the valve clearances first and making sure that the decompressors are not interfering with the valve operation. I often roll small engines over with a breaker bar on the crankshaft pulley bolt, you can learn a lot about what is or is not happening inside an engine by quietly doing this… even the sound of the injector buzz and cylinder leakage.
Stop using ether, 3GM’s already have a history of broken ring lands, if you need to add heat to the equation use a paint strip blower gun or blowlamp, ditch the ether.
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Old 28-05-2024, 15:08   #9
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Re: Yanmar 3GM30F Hard Starting

It would be good to know when the compression tests were taken.

There are few reasons why the engine was hard to start after the work was done on the fuel system; timing being one of them but there are others. If ether was then used and especially if used incorrectly (i.e.too much etc), rings or lands may have been broken by the use of the ether complicating the fault analysis.

I suggest another compression test ASAP to confirm the previously reported numbers. If the new test confirms the earlier results (160, 170, 160), then that issue must be addressed; they are far too low.

If the new test show better figures (i.e. high 300s - low 400s), then keep looking at fuel issues.
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Old 28-05-2024, 20:37   #10
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Re: Yanmar 3GM30F Hard Starting

Compression test was performed after the injector pump and injectors were rebuilt and the engine wouldn’t start well. I will look into testing compression myself when I am able.
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Old 28-05-2024, 21:17   #11
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Re: Yanmar 3GM30F Hard Starting

Was the compression tests done before or after the ether use? If before, then suspect the injector sealing. If after then it is either injector sealing or broken rings / lands from the ether.

Was the ether used as faint whiff into the air intake or a decent spray? The faint whiff is the correct way if you really must use it but as SkipperP notes, it is best not to even try it. A decent spray will break stuff in an indirect injection compression diesel (e.g. Yanmar GM series).
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