Hard to start 3gm30f.

[David law]

Hey can anyone give me focal point to look at that may be why my 3gm30f is hard to start and when running either cold or hot, has a shudder or a miss every 8 seconds at 1000 rpm?

I've had the engine rebuilt, injectors and hi pressure pump rebuilt by experts. Changed hoses and brass washers from tank to the injectors.
Any ideas would be appreciated. Cheers, David.

[CaptRob725]

Check the raw water mixing elbow for blockage. I just had the same problem and sure enough the elbow was restricted so much the back pressure was keeping the engine from starting. Also check the Waterlock muffler for obstructions. I replaced my Waterlock since it appeared to have the start of a crack I. It. I also did a muriatic acid dip for the elbow. A 30% solution overnight did the trick. Dried and repainted it and reinstalled it. Hope this helps.

[David law]

Thanks Capt. Rob.
That makes a lot of sense. I'll get right on that. Cheers, Dave.

[sailorchic34]

It is very possible it's a very clogged discharge elbow. That 8 second stumble could be a sign of that. You would not get that with broken rings for example..

If it's not the discharge elbow, do the following test. With the engine running, pull each decompression lever one at a time, open and then close. What you want the hear is the same amount of stumble with each cylinder. If one cylinder makes little difference, then that is the problem child.

Hard starting hot and cold is generally a sign of low compression, which could be just in one cylinder and with a rebuilt engine, perhaps a broken ring or two. It could also be a injector or pump timing. But you don't get a 8 second stumble with a broken ring or timing issue.

[David law]

Thanks for the response Sailorchic34. I took off and looked at the mixing elbow off and there was no clog, free and clear. I'll try that decompression thing on each cylinder today. Thanks. I suspect there is a micro air leak possibly in the racor housing. After I've been running for some time I took off the top bolt on the racor and noticed there was a half an inch of air at the top. Is that not supposed to remain tight an airless? Could that explain why when the engine has been shut down for 24 hours the fuel falls back to displace the air, hence not have a tight fuel charged system upon cold start up? Cheers, David.

[jkishel]

Sounds more like a fuel supply restriction than an air leak. The "air" you see in the Racor is possibly a vacuum caused when fuel consumption exceeds fuel supply. The void refills with fuel over time when the engine is off. Check fuel tank vent, change fuel filters, check pickup, etc.


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[hamburking]

I had a yanmar 3gmf. Had similar trouble, hard to start, running rough, until I ran aground. To get off the rock, I revved the snot out of it. A few minutes of high rpm did the engine a world of good. I usually keep the revs low, for quiet and low vibration. However, it seems I needed to burn the crud out of wherever it was building up. After that, it started easily, and ran much better than ever.

[Xthewater]

I had a similar problem turned out to be a loose hose clamp between fuel pump and tank allowing a small amount of air to be sucked in, engine would stumble and hard starting.

[duefocena]

Cumbersome and sometimes arduous, I've taken a piece of clear tubing introduced it inline from the racor to the pump to view any air bubbles. Found I had an air leak inside the tank at the lift tube.

[David law]

Thanks again to everyone for all the input. The problem of hard starting and with a miss every 8 seconds has been solved.
After doing everything, everyone suggested, While the problem still remained, the only thing left had to be fuel, or fuel pump.
A good friend told me to put this stuff called Sea Foam, one can into the fuel tank, and did a 2 hour run on a windless day at 29 hundred RPM. The next morning fired up easily and purred like a kitten. No miss or shudder. Bought it at Canadian Tire.

[hamburking]

Originally Posted by David law

Thanks again to everyone for all the input. The problem of hard starting and with a miss every 8 seconds has been solved.
After doing everything, everyone suggested, While the problem still remained, the only thing left had to be fuel, or fuel pump.
A good friend told me to put this stuff called Sea Foam, one can into the fuel tank, and did a 2 hour run on a windless day at 29 hundred RPM. The next morning fired up easily and purred like a kitten. No miss or shudder. Bought it at Canadian Tire.

It wasn't the sea foam, it was a good long run at 2900 rpm.

Could you do everything all over again without the sea foam so we know for sure?

[David law]

Yes.
1. The Motor was rebuilt in 2013, along with the injectors and high pressure fuel pump.
2. All new hoses double clamped along with all new cooper washers from the tank to the injectors including the fuel return back to tank.
3. With engine running, cracked each cylinder at the injector to see if the miss was high pressure pump, or injector related. Not. The miss was still there on any 2 cylinders.
4. Vacuumed air vent to fuel tank and found a partial blockage there. Water from washing the boat. Avoid spraying water in the air to tank intake.
5. Removed fuel return line at tank to injectors and blew out any possible clogs there.
6. Bypassed the Racor filter. Not it. Reconnected.
7. By passed the lift pump with gravity fed fuel. Not.
8. Took of the mixing elbow and was found to be clear.
9. Loosing my patience at this point.
10. After all this and 3 days later I decided to run the motor for an hour at different RPMs to try and clear all the lines after everything I've done.
The Shudder/Miss was still present.
11. While coming back to port on a windless day I put in this stuff you can get at Canadian tire called SEA Foam into the fuel tank. Ran engine at 2900 RPM for 2 hours. The next day the engine fired in 2 seconds and the shudder was gone.
I don't know, you tell me.

[Tx J]

It had to be the Sea Foam dissolving either some slime/snot in the fuel system, coked up combustion chamber(s) and/or rings, or crud sticking the valves then. Unless you have a really weird electrical gremlin that will be back.

That Sea Foam liquid (and a spraycan of almost the same stuff, the name of which ICRN) can work wonders, great stuff. Try to run it all out though, probably eat something up if it just sits in the fuel system.
I've always used them on outboards, didn't know to use it with diesel, going to start, thanks for following up.