What just happened??

centerline · Mar 29, 2014

it sounds like you got a bad injector nozzle.... but you must keep in mind, the new nozzle may look identical to the others, but if its metered differently, it could cause it to sound like that and will definitely cause problems... if it is delivering more fuel, or less fuel than the others, that cylinder will run rich or lean, and in either case, severely damage the motor if you try to run it under a load.
look for any identifying marks on the nozzles or take them both to a diesel pump repair shop and have them determine if they are metered the same.... and while your there, have them repair the leak in the perfectly good "old" nozzle...and keep running it.
its always better to be safe than sorry, as you have just found out... your a lucky man to get that second chance...

capta · Mar 29, 2014

I'm pretty sure all the injector models for a particular engine look alike. But there are at least several different injectors for each application of an engine. A farm tractor motor may have the same basic Kubota block as does a generator or marine engine, but almost every other bit that goes into making an engine suitable for it's application, is different. Rings, pistons, push rods, fuel distribution pumps, injectors, turbos or intercoolers may all be application specific.
If your injector is leaking around the base, it is probably the compression washer. If somewhere else, then I'd service them all, keeping in mind the "black box theory". As for the knocking; diesel is the cylinder lubrication, so if the injector isn't functioning to this engine's specifications, then perhaps the cylinder wasn't getting enough lubrication. Perhaps?

StinkBug · Mar 30, 2014

Diesels with the wrong amount of fuel will make awful knocking noises that sound just like a gas motor with a spun rod bearing. Hell my diesel pickup makes varying amounts of knocking noises depending on load and it's completely normal, but would scare the hell out of me in a gas motor. Sounds like the injector you got was either bad, or just for the wrong application. As was mentioned marine engines see a different type of loading from other uses and the injectors are a vital component in how the engine runs. I wouldn't expect one to make your engine run that badly, but it is a possibility.

I'd say simply a bad injector is much more likely. I can tell you from working in auto parts that every part you buy has been dropped or tossed across the back room at least 3 times. I'd return it under warranty and either get your money back or get another one and verify that the part number you are using is the same as the part number you are replacing.

Chris Patterson · Mar 30, 2014

Yep. Me? I would carry ALL of the nozzles to the diesel shop so they will be matched. Very important. Doesn't sound like anything wrong with the engine proper. Sounds like they are due anyway.

Which is a good 'tune up' option for anyone with an ageing fueler..

Me and Boo · Mar 31, 2014

Injector knock will have you ready for your engine to grenade. Various reasons for it to happen. Since it is over, most likely was a speck of dust or "thing" went into the injector and it took a few revolutions to pound it up and run normal again. Had it happen in one of my trucks in the middle of no where in Wyoming once. All I could think of was a week in the back country before anyone would start looking for me. It followed the writing of "this too will pass" (a useful phrase after eating a bad oyster too).

robertsapp · Mar 31, 2014

An injector that fires late will make a loud knock, because the fuel is introduced into the cylinder too late in the compression cycle and explodes instantly. Maybe something in the injector jammed it up and caused it to fire late. That's my contribution to the speculation.

bananabender56 · Mar 31, 2014

robertsapp said:
An injector that fires late will make a loud knock, because the fuel is introduced into the cylinder too late in the compression cycle and explodes instantly. Maybe something in the injector jammed it up and caused it to fire late. That's my contribution to the speculation.

Had the same thing with a Yanmar 4J, large knocking sound so shut down engine. Removed suspect injector and had it overhauled - all good.

weinie · Mar 31, 2014

I'm no expert, but did you get paint chips or dirt in the intake of the injector prior to installing

civilwar1969 · Mar 31, 2014

Sounds like a bad injector or the wrong injector. Might look the same but there should be numbers on the side of them they should match. If not have maybe napa cross refrence it to make sure its the right injector. The injectors are all timed differently even if they look the same so thats why you have to make sure you have the right one.

Bill Roosa · Mar 31, 2014

If it knocked "all the way down to stop" then I'm thinking it is still injecting fuel (leaking) Given that the fuel cutoff was pulled that does not sound like a injector stuck in the open position but does sound like a bad one that just leaks. Since it started and ran fine for a while I'm thinking dirt in the injector or it broke.
Good luck

bobbyfingers2001 · Mar 31, 2014

Here is my two cents:

1) The new injector is a larger orifice thereby injecting too much fuel during each cycle which ignites with way more force than the others causing the resounding knock (which will destroy the engine).

2) The new injector is stuck open or defective in some other way causing the same result as above.

3) Not knowing how long it knocked, you may have not gotten out all of the air in that injector line and ran that cylinder dry for a minute causing the knock.

4) Again, not knowing the run cycle before this, you could have dry sumped the crank case.

5) You mentioned replacing a bunch of fuel system parts & filters and may have pulled some air or water into the fuel rails.

6) The fuel return line(s) may have been blocked causing fuel back pressure.

Paul Beauchamp · Mar 31, 2014

don't overthink the problem

In determining your problem it starts with how the system works. The fuel pump sends the right amount of fuel at the right time. The injector is simply a poppet valve. When the highly pressured fuel hits it, the injector opens and allows the fuel to spray into the combustion chamber. The fuel ignites, you have combustion. Simple
But what is not simple is the relationship between the injectors and pump. They must match, not close, not good enough but match exactly. So you have either a mis matched injector or a faulty injector. My money is that the injector is wrong not faulty. It must have the following, same number of spray nozzle holes, same size of spray holes, (the holes are critical never try to clean them mechanically) same cracking pressure and same cc's of fuel displacement. What i would suggest is to take your old leaking injector to a diesel injector/pump rebuilder. They will either be able to repair your old one or give you the line on a correct injector.

James10016 · Mar 31, 2014

J_Schoenfeld,

I reccomend that you take a more systematic approach to the problem and let the facts speak for themselves after you've looked into the matter a little closer yourself. I rode on diesel equipted M60 tanks for years while serving in the US Army. It seems that everyone immediately assumed that they had a bad fuel injector whenever their engine wasn't running properly. This is NOT to say that you don't have a bad injector, just let common sense and the process of elimination support that assumption.

Use the power of the Internet to provide you with Insight, Tips and Techniques such as this YouTube video on simple testing you can do for identifying bad injectors.
http://www.youtube.com/watch?v=GDJoKIoSd-w

Also here’s a list off the internet pertaining to the 5 most known signs that indicate a bad fuel injector. Does sound like you have a sympton #2.

1. Abrupt Engine Power
It is easy to understand that when a fuel injector is clogged, the fuel supply will be irregular too. With such lopsided flow, the engine will fluctuate between low and high rpm’s causing it to deliver the power in chunks, rather than being smooth and gradual.

2. Engine Misfire
In case when the injector keeps on struggling against the clogging of foreign particles, a time may come when it might miss out to supply the fuel completely when it is required to. Thus, the engine results to give a compromising performance. The engine will misfire which can easily be felt while running. This is really a bad sign and requires immediate response because misfire would give rise to engine overheating and pre-igniting the fuel mixture.

3. Rough Idle

Damaged fuel injector will not only give weird problems while on the go, the effects will persist even when the engine is running idle. Instead of a smooth engine idle, it will be rough and irregular when the fuel supply is abrupt.

4. Leaking Fuel
Apart from those internal chokes, fuel injectors can turn out to be bad even due to external cracks developed on the exterior body part of the injector. This damage is common for those injectors fitted on to the intake manifold. These cracks can cause the fuel to leak from the body, rather than flowing through the nozzle, which can be seen and smelled easily. The leaking fuel, instead of being sprayed in atomized form, flows in the manifold in the form of droplets. This will cause the air fuel mixture to turn out weak, giving out poor engine efficiency.

5. Reduced Gas Mileage
It is obvious, that a damaged fuel injector would either cause the fuel to be wasted by leaking from the body or would supply excessive fuel when the internal springs are damaged. These conditions will undoubtedly lead the engine to run poor reducing the gas mileage.

Good Luck!

James

scamps · Mar 31, 2014

I had the same problem, lack of knowledgeable advice from local repair services I encountered a runaway diesel. This resulted in a engine rebuild, trying to source the problem of the engine knock. The last check made in my scenario was a pressure test of my injectors. This test revealed the source of my problems. I would suggest that you remove your injectors and take them to a repair shop that has the equipment to pressure test your injectors to factory specifications. I would then remove the high pressure pump and also have it pressure tested before considering an engine rebuild. Note: I went through the same scenario as you have indicated except that I had zero fuel leaks and oil leaks other than the infamous Perkins rear seal weeper. (Perkins 4-108)

Jake N Eggs · Mar 31, 2014

All valid possibilities in the posts above. One other possibility is that there was some carbon dislodged by removing the old injector. The dislodged carbon can get stuck on the top of the piston and is compressed between the piston and the head. It would continue to knock as the engine is shut down. When the carbon cools it can loosen from the top of the piston and get blown out the exhaust in the next run cycle.

Chris Patterson · Apr 1, 2014

The mechanics axiom: If there's a problem, go back to the last thing you worked on.

I have found this to be true way more often than not..

garymckin · Apr 1, 2014

Just remember changing to one new injector will have a better spray pattern than a worn injector. It's better to change all injectors at one time to equalize your engine. Also make sure that new injectors are for your application.
check all injectors would solve the problem.
Good Luck
Gar

nutheastah · Apr 1, 2014

My experience tells my you should bring the new injector to a good diesel shop and have it checked. It is quite common for stuff to fail either when it is first installed or when it is at the end of it's life. Who knows what went on to that injector before you bought it such as improper assemblyat the factory, dropping or improper storage etc.etc. . All diesels need two basic things. air and fuel which must be sent to the engine at precicely the correct time. If the injector sticks as one fellow mentioned because of a speck of dirt or rust in side it or because it wasn't assebled corectly or a dozen other reasons then the fuel spray could be delayed or just dribble into the cylinder. that delay will cause a change in timing of that cylinder. And a knock as the piston takes a beating because combustion comes too late.
Another possibility is that when you pulled the old injector out carbon from around the tip dropped into the cylinder and worked its way between the piston and the head.If that is the case then the problem has flown out the exhaust and you will not experience any more knock. But of course you will for a time live in constant fear because you cant locate the problem. Working on and around diesels for 40+ years I have experienced both of these problems from time to time with just the symptoms you described. These are the moments when the mechanics heart is tested. Truth is that if it was running good before you worked on it then it was most likely something that you did. That's a good thing.It makes it easier to diagnose.If the problem doesn't come back, then hit the plus key on your calculator.
Bruce

ComPac Allure · Apr 1, 2014

Hi:
Nothing wrong with the Kubota injector or glow plugs. I've using them in my M12 (same engine) for years. I even had the new and old injectors checked out by a local diesel shop. All four performed the same (there was nothing wrong with the two I took out). I wanted new glow plugs and injectors in the motor. Yes, the copper compression washers need to be changed each time you remove the injectors. Also set the tappets and it quieted the motor down a bit. I would suspect some kind of crude might have fallen into the cylinder and made a carbon knock until it got pushed out thru the exhaust port. I was surprised at the compression that these little motors make. Mine warm when tested pumped up to 480 lbs an the other was 505 lbs (within 5%). Don't know what else to add but I see no problem using Kubota parts. Another member of my sailing group purchased and engine water pump from Kubota and saved a bit of money as well and worked perfect. Good luck...