Injector knock

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Injector knock

Postby mike cunningham » Wed Feb 14, 2018 12:49 pm

OK, for the record. I had white smoke and hard start once again after about 45 hours since replacing injectors. I also had a really bad engine knock which made me think something was seriously wrong. I figured what the heck, might as well cange injectors again before I completely freak out.

Did the change out and both the smoke and the knock went away.

So the moral of the story is bad injectors can cause all sorts of wired noises. Including snapping and knocking, both of which I have experienced.

Now I have to figure out what's causing them to gunk up. Most likely gunk in the fuel. That sucks because I just did a complete fuel system cleaning.
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mike cunningham
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Re: Injector knock

Postby BillSmith » Thu Feb 15, 2018 1:09 am


What have you got in the way of filtering inline before the injectors? In our odyssey to get our engine 'right', realized that getting out in some chop would kick up all those microbes and put more particulate matter into the fuel lines. The Raycor seems to be keeping up with anything of late.

We have had white smoke since Day One of owning this engine. (Perkins MD-30) Have been told that is indicative of water in system. Not coming from fuel based on clarity in filter bowl. Hopefully something in the exhaust mix. Pray that it is not a leak into cylinders!

Ours has never been overly difficult to start. Cranks longer if it has been sitting for weeks, but always fires up in reasonable fashion. But white smoke after every start after a night off. No smoke if coming back into harbor after only a day's sail.

We have had injectors cleaned and about to be replaced, for other reasons-misty leak, probably over-torqued at some point.

I know jack-squat about diesel. Know that knock in a gasoline engine can be poor fuel, delivery and the like. Worried about your and our white smoke giving pause for thought that 'noise' could be water in the cylinders, which in a diesel is apparently no Bueno, in Grande fashion.
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Re: Injector knock

Postby mike cunningham » Thu Feb 15, 2018 2:07 pm


My filters consist of a Racor water seperating filter and bowl as primary and the standard Yanmar engine mount as secondary. I installed the Racor about a year ago after the Hawaii trip I when noticed white smoke and during troubleshooting realized I had the incorrect primary filter installed. It was a water seperating gasolene filter with no bowl. Don't ask me why it took me 15 years to figure this out.

So, in addition to completely cleaning the interior of the tank (I installed an inspection plate years ago after experienceing a pickup blockage) I changed out the primary to the Racor set up and also replaced the secondary. Both showed some signs of water ingress which was not suprising considering anout twenty at sea re-fuelings took place during the return trip from Hawaii.

Regarding water or oil being the root cause of the problem. I would expect to see some coolant consumption if it was water and there has been zero consumption. Same with oil. Although I do burn small amounts of oil, it does not seem excessive. About 4 ounces in 24 hours of engine operation.

Based upon what I have read, the white smoke with a little water sheen at the exhaust is typically indicative of incomplete diesel burn. The smell is also pretty noxious, especially if it is wafting into the cockpit. This can be caused by faulty injection (injectors, timing, or hi pressure pump, crappy fuel) low operating temperature (thermostat), poor compression ( an expensive one), or insufficient air intake (blocked filter). I have also read about injector knock but didn't really believe what I read until this latest experinece.

The air and the operating temp are easy checks. I have a compression tester but have not used it because injector replacement has solved the smoke issue before I had to attempt a test. As mentioned above, I elimated water and oil because I donlt see any unusual consumption. So I am pretty much left with bad fuel which could contain some water I suppose, but you would think the Racor would deal with what little there might be and I see no water in the bowl. I also use a fuel additive - diesel dry - which is supposed to help with any moisture but now I am beginning to wonder if it might be a contributing factor.

With regard to your smoke, what you are seeing seems to be pretty consistent with normal ops. Smoke when you start and a little while you warm up. On cold days/nights I have noticed some steam out of the exhaust but I think that is pretty normal. The hot exhaust gas contains a little wator vapor as a result of combustion which, I imagine, is magnified by the wet exhaust system. I usually get a start on the first few cranks. If I have to crank for more than two seconds or so I start to get paranoid. This may just be a fact of life as the engine ages. I have about 1250 hours on the engine now and have been putting a lot more hours on in recent years since I have been coming up to the Bay for races. Each trip puts about 24 hours on the engine. Mind you, the engine is also 33 years old.

So we'll see how this latest injector replacement works out. Hopefully the last vestiges of contaminants are out of the system.
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