Yanmar 3GM30CF Hard Start

[Characracker]

Hi Everyone,

I’m brand new to the forum and I’m hoping to get some advice on a hard start issue that I’ve been having with my 2003 Yanmar 3GM30CF with 2500h on the clock.

History of motor
I’ve had the boat for 3 years now and the engine has been pretty reliable, although I’ve always found it a little hard to start (especially in winter). It seems to start up fine (at idle speed), but within a few seconds it would stall. At 1/3 throttle it starts up without any issues and you can throttle back to idle within 10 seconds or so before stalling.

What the motor is doing now
Recently though, the engine has been extremely hard to start from cold. It’s been particularly bad since the last service I did on it (although I’m not 100% sure if it coincides). To be able to reliably start the motor now, I need to have 2/3 throttle and crank the motor for a good 10 seconds for it to start spluttering to life. While it’s starting you can see black smoke coming from the exhaust. Eventually it kicks in properly and the engine revs up. You need to keep the revs quite high for another 10 seconds or so before being able to go to Idle because if you start reducing RPM too soon the engine seems to lose power and stall.

Once back at idle the engine behaves normally. No black smoke and it seems reliable.

If I switch it off and start soon after, it starts fine. If I sail for 1-2h with the motor off it becomes hard to start again.

Troubleshooting done so far
* I replaced the fuel filter (the one bolted to the side of the engine) as part of the last service. The old filter looked clean but I replaced it anyway. Since then I’ve had a slight leak at the fuel filter because I wasn’t able to get the retaining ring on tight enough, but since then I’ve taken the fuel filter assembly completely out of the boat, tightened everything up with a vice, and it doesn’t seem to be leaking anymore. I can’t see any obvious fuel leaks anywhere else.

* Two years ago, I took the fuel injector pump out (I don’t remember why, I think I was trying to take the gear timing case off to fix a little oil leak), and when I took it out, I damaged the shims that sit between the fuel pump and timing gear case. When I put it back together again there was a small oil leak from where the shims were. Since then, and at my last service (the engine became harder to start after this), I took the fuel injector pump out again, flattened out all the shims using a vice and sanding with fine wet and dry sandpaper and putting it all back together again. That fixed the oil leak.

* I recently checked the fuel timing by taking out the starter motor, and disconnecting the high-pressure fuel injector line to the number 1 injector. I’d watch the end of the high-pressure line (which is no longer in the injector) for when fuel would start dibbling out as I turned the crankshaft manually. I took a photo of the timing of when fuel would ‘start’ to appear from the end of the high-pressure line (see attached). I’m a bit confused of how much fuel I should see appearing out of the high-pressure line to do the timing. Is it when the very first appearance of fuel or when the bulk of it comes out? The attached photo is when you just first start seeing a tiny bit of fuel, but the bulk of it comes out right on the marker.

* Replaced corroded Exhaust Elbow in 2018 with a stainless steel one (not done recently but I think it’s relevant).

Any feedback would be much appreciated.

I've also attached my full service history of the engine in case anyone is interested. I wonder if something I've done or disturbed in the past might have caused the hard starting problem.

Thanks to everyone who has any feedback or ideas in advance.

[tkeithlu]

Welcome to the forum, Characracker. Now I'll go back and read your post.

[tkeithlu]

Black smoke is incompletely burned fuel. The most common cause is too much fuel per injection, such that the supplied air cannot burn it all. I'll leave it to you for how to reduce the fuel per injection.

A seconday cause is low compression, with leaks around the pistons and the valve stems. Let's hope that that's not the problem, and that you can solve the problem by leaning the mixture.

[Cpt Mark]

FWIW, I have the same issue in my Yanmars, same engine similar hours. When it's warm out they start fine. Once it gets cold not so fine. And it gets cold enough to snow here a couple of times a year.

[hugosalt]

Not addressing cause of hard start, however my experience in cold weather starts of our
3GMC when sailing thru winters here in New York's Long Island Sound.
Throw the 3 decompression levers and turn over motor then back to compression and start motor with 3/4 throttle (as recommended by Yanmar for cold starts).
May help?? with your stalling.

[team karst]

THis is a non glow plug motor? It would seem that it will be sensitive to lower than usual cranking speed, and loss of engine compression; both critical for charge heating.

[Characracker]

Hi Everyone,

Thank you for your quick responses.

In Sydney, Australia a cold day this time of year might be 20ºC (68ºF). Even on a hot day 30ºC (86ºF) it seems to have trouble starting if the motor has been off for a hour or two.

@Team_karst - No glow plugs on this motor

@ Tkeithlu - do you think that retarding the fuel timing might reduce fuel input? Also, once it's started up, I don't get any smoke at all.

[Captndave1]

Have your injectors serviced

[gonesail]

my yanmar mechanic said to give them 75% (or more) throttle when starting in cold weather. have you checked your fuel lift pump lately? a shame that yanmar did not put glow plugs in these engines.

[j.g.evans]

I had similar problems on a 3HM. I also had oil leaks around the pan. With hindsight I think my issue was poor compression with blow by of the rings. A cheap way to check compression is with the engine warm try using the compression release levers to start on one cylinder. I diagnosed a bad cylinder on a friend's boat this way. I wonder if running the engine without the dip stick would indicate blow by. Perhaps others have had experience doing this. I replaced the 3HM with a 3GM30 thinking I would get more HP. I got a much lighter duty engine with less HP. I should have rebuilt the 3HM.

[Compass790]

After looking up your service history I would suspect an air leak somewhere. If you can pressurise your fuel system do that & wrap all the joints in dunny paper before testing. Leak may well be in the fuel filter. Its telling that its hard to start again after 1hr & also that problem occurred after your last service.
If you still have problems I'd be checking for a lazy cylinder as described upthread.

IMO there is no need for you to buy Yanmar branded 30w oil, ( Yanmar dont make it) any reputable 15w-40 diesel oil CD or above rating would do but in Sydney I'd probably go for Penrite 20w-60 diesel oil. YMMV

[Hoodsail]

you note that your yanmar is hard to start when cold, taking 10 sec of cranking. I would offer the opinion that that's within normal time to crank over a cold diesel before starting. Black smoke after starting w/ 2/3 throttle is definitely unspent fuel, confirmed by your comment that smoke clears shortly after running. 2500 hours is not much use for a diesel. You could have a mechanic do a compression check as a baseline. Be curious if compression is consistent across all cylinders. Does your engine have an air filter? give it a check and replace if appears dirty.

[sinnerman]

I have the same issue with my Universal Westerbeke M25. By design these engines will not start without glow plugs, however I still plan to perform the following:

(1) Adjust the valve clearances.
It has probably NEVER been done and this is a 35 yr old boat. The valves tend to wear deeper into their seats with age, resulting in less valve clearance and less power.

(2) Run Liquid Molly "Diesel Purge" through the system.
This stuff will clean the injectors and pump' s internal parts, most importantly their internal check valves. You put this stuff in an external container (old water bottle) then route a pickup hose from the container to the fuel intake line on the pump and the fuel return hose from the injectors back (the one to the fuel tank) back into the container. Then run the engine. The stuff circulates in a closed loop acting in place of the fuel and cleaning out the varnish.

There is a YouTube channel of a Mercedes mechanic who swears by this stuff. He also has good info on injectors:

https://www.youtube.com/watch?v=14nQo2E5pAU

(3): Remove the injectors and run a compression test. (Needs to be done after setting correct valve clearance.) I will do this at the same time I remove the injectors (below), since the compression tester needs to be hooked up to the injector ports.

Per the engine manual , there are min limits for the pressure and it cannot have more than a 10% difference between the three cylinders. Since the engine is not blowing any "blue smoke" (except a very slight amount on startup) if there is low compression it is most likely a valve issue, with a burnt exhaust valve usually being the culprit.

(4): Have the injectors tested, cleaned and pressure re-set.
My engine has a lot of pinging (called "nailing" in diesels) which is usually the result of the injectors not sealing completely after firing ("dribbling").

The fuel leaking into the engine cylinder / pre-combustion chamber ignites on its own before the injector actually "fires", causing a "pre-ignition" or "knock".

Cheers...

[phantomracer]

If it is a European model, it could be the valve on the injector pump. if it leaks, there is not enough pressure to open the injectors. $20 part that kept my 3gm30f from starting time to time!

[Characracker]

Thank you all for your advice help. I have managed to resolve the problem.

As per the advice of j.g.evans and Compass790, I checked to see if there was a lazy cylinder. I did this by starting the engine and then pulling the decompression lever on each cylinder to see what difference that made.

Pulling the decompression leaver for cylinders 1 & 3 made the engine sound like it was about to cut out (which Is what I would expect), but when I pulled the decompression leaver on cylinder 2 there was almost no impact at all.

That lead me to believe that cylinder 2 wasn’t doing anything at all and that the motor was running off cylinder 1 and 3 only.

I pulled the injector out from cylinder 2 and tested it by leaving it connected to the high pressure line but pointing away from the engine so that you can see the spray (or lack thereof) coming out. The process is demostrated well in this video for a similar motor:

https://www.youtube.com/watch?v=HxVfDIcTP_w

Sure enough, no spray. So, I figured it was a bad injector. Then I tested it by swapping the cylinder 1 and 2 injectors but the injector that I thought was faulty was working on Cylinder 1, and the injector that I knew was ‘good’ wasn’t working on cylinder 2.

Next, I took off the high-pressure lines for all cylinders, and took the valves off the fuel injector pump and gave it all a good clean with some Throttle Body and Carby Cleaner spray and paper towels. It already all seemed pretty clean but this was all easily accessible and easy enough to do so I thought I’d give it a try.

Once clean, I retested to see if I could see a spray coming from the injector on cylinder 2 (using method described in the YouTube video) and to my delight it stated firing!

I put it all back together, blead the system and to my delight the engine has been starting up perfectly ever since.

I don’t really know how I fixed it (after all I just gave it a clean), but I do know that it was some sort of fuel delivery problem going to cylinder 2 only. I think phantomracer in the post above was right, it was a bad (or dirty) valve on the fuel injector pump.

Again, big thank you to everyone on this forum!