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terrylad · 18-07-2012, 05:48

My 3GM30 runs fine at 1850rpm in forward or reverse. Over 2000 rpm the engine emits a loud "clacking" sound and starts to misfire. The exhaust chuffs out blue/white smoke. Increasing the revs produces blackish smoke and the engine loses rpm, sometimes shutting down. Easing the throttle back allows the engine to recover and run on all three cylinders again (under 2K rpm).

I have changed filters and bled the system. To check that the fuel was good I ran the engine with the intake and return fuel lines running into a bucket of fresh diesel. I also ran a can of "Diesel Purge" through the engine while running under load. This did not change the symptoms of higher rev failure. Obviously, I suspect that I have one or more sticky injectors, but I don't know for sure.

I tried to isolate the injector by using the decompression lever one at a time with the engine under load. I could not detect the symptom of failure at any rpm, which seemed to limit at about 2250 on two cylinders.

I'm reluctant to pull the injectors, assuming that they will be well and truly stuck. I've heard that you can release the injector flange nuts a few turns and then crank the engine, allowing the compression to budge the injector up a fraction of an inch, breaking the initial seal. Is this a reasonable way to coax them out?

Have you seen these symptoms before? Can I do the necessary work to effect a repair myself with basic boat tools?

I'd greatly appreciate your response.

**GordMay** · 18-07-2012, 06:10

Greetings and welcome aboard the CF, terrylad.

See Chapter ‘X’ ➥ http://j30.us/files/yanmar-manual.pdf

Or ➥ http://j30.us/files/YanmarGM&HMWorkshopManual.pdf

S/V_Surya · 18-07-2012, 07:41

The make an injector pulling tool. I would see if I could rent one.

djmarchand · 18-07-2012, 09:06

I have pulled injectors on the 3gm30 engine with basic hand tools. Make sure you use a new crush washer under the injector when replacing them.

You symptoms do sound like poor injectors. They pop early and have a poor spray pattern. That causes a build up of fuel in the cylinder that finally fires with a bang.

Take them out, pop and spray test them and rebuild or replace. Replacements are not much more expensive than rebuilding- about $120 each.

David

**Cheechako** · 18-07-2012, 09:22

You may have a cracked piston, as happened on both my 3GM30's..... hope not. If it runs fine up to 1800 rpm.. I doubt it would be an injector issue...?

terrylad · 20-07-2012, 11:58

Pulled the injectors this morning. They came out nicely with no forcing or puller needed, just a slight turn with a spanner and out each one came by hand.

They look pretty good with a small circle of carbon on the face of each one, the #3 having a bit more than the rest. I've got them being tested as we speak. Will post results FYI.

neptunesjester · 20-07-2012, 12:31

My buddy just fought the same symptoms on his 2 cylinder yanmar. Would start to miss, then blow black smoke then die as RPM's increased. Turned out to be a fuel supply problem - had a cracked fitting on the tank that would allow the fuel system to suck air as demand increased.

If your injectors test OK, try running the engine off a portable tank, eliminating the existing fuel lines. Also check your lift pump pressure to make sure it is supplying enough fuel to the injection pump at all RPM's.

Later,
NJ

terrylad · 20-07-2012, 15:46

I have run the engine bypassing the tank/Racor from a bucket of clean fuel, and got the same symptoms of misfiring, clacking, white/blue smoke over 2K rpm. However, that did not eliminate the lift pump. I did find a banjo fuel connector had come loose a few turns and was spraying fuel, which, incidentally showed me that the pump had some substantial pressure going. Tightening the fitting (located on the lift pump) didn't make any difference to the symptoms (dammit!).

I will go over the connections carefully and rehab as necessary just in case. It's very interesting to hear about another set of symptoms that mirror mine and the fix for it. Thank you.

**twistedtree** · 20-07-2012, 17:57

You said you replaced filters. Does that include the air filter? I think an air restriction could cause your symptoms too.

Jentine · 20-07-2012, 18:25

Isolate each injector by loosening the fuel line to each nozzle with the engine running to determine which is the problem. If there is no change in the rpm of the engine, I would look elsewhere for the problem. Have you checked the pump timing? Diesel engines are quite simple. All they need is a supply of fuel and air and compression in the proper mix and you are good to go. If the timing is ok and the nozzles are ok and the air is not restricted and you are getting enough fuel to the pump, I would suspect the injector pump.

**twistedtree** · 21-07-2012, 05:13

Quote:

Originally Posted by Jentine

Isolate each injector by loosening the fuel line to each nozzle with the engine running to determine which is the problem. If there is no change in the rpm of the engine, I would look elsewhere for the problem. Have you checked the pump timing? Diesel engines are quite simple. All they need is a supply of fuel and air and compression in the proper mix and you are good to go. If the timing is ok and the nozzles are ok and the air is not restricted and you are getting enough fuel to the pump, I would suspect the injector pump.

What does it mean to check or adjust the timing on a diesel injector pump? I thought the pumps were direct drive, gear driven. So for timing to be off, the pump would have to have been installed wrong, or have skipped a cog in the gears. Or is there more to the mechanism than I'm aware?

perchance · 21-07-2012, 07:12

I believe the timing on these engines is changed by adjusting the shim thickness under the pump base. Blue/white smoke indicates unburned fuel and black is a symptom of incomplete combustion. My suspicion is something inside the injector pump is wonky.

terrylad · 22-07-2012, 06:34

I just had a thought about these symptoms. It really looks like weak fuel pressure is causing them. Even though the lift pump has tons of pressure...

I originally installed an in-line squeeze bulb pump between the tank and the racor primary filter. This has been really useful in priming the filter and the fuel lines instead of the usual wanking away on the lift pump when the system needs bleeding.

Maybe that squeeze bulb is weakening the fuel pressure pulse from the lift pump when the engine is running at high load......Suction from the lift pump diaphragm on the inlet side could be absorbed through the racor by the squeeze bulb, which would pulsate with each pump cycle.

Hmmm.......I hate to lose the utility of that squeeze pump, but I'll certainly get rid of it to hunt this problem down - after I get the injectors back next week.

**Cheechako** · 22-07-2012, 11:31

I have used a squeeze bulb effectively on a couple of boats with no issues...

terrylad · 24-07-2012, 05:20

Injectors tested OK. Just remembered that it can't be the squeeze bulb because I had the symptoms while running the engine out of a bucket of fuel. I have a bunch of new banjo washers and I'll be putting it back together today.