Help!! Loud Engine knock after changing glowplugs

[wvpolekat]

Sounds like you got the problem resolved. Good.

If it continues, I think you should explore all options with the injection system first.

So, first off, a bad injector on a mechanical injection engine does not affect timing. Second, idling diesels do not fire prematurely from hot carbon. They can't, there is no fuel there to fire until injection occurs. However, an injector can fail by making a poor spray pattern. This means more of a jet of fuel than a fine mist. When this happens the fuel ignites with more of a bang and a knocking sound. It also makes a lot of carbon.

I suggest you crack the injector line on the carboned up cylinder, while the engine is idling and knocking. If this stops the knock and makes it run rough, you know it's an injection problem.

If it is an injection problem on that one cylinder you'll need a set of injectors, or yours rebuilt by a qualified diesel shop. And when you get that taken care of go out and work it at full throttle for a while to clean out the deposits so the corrected spray pattern is not spraying on a carbon buildup. It needs to spray cleanly into the combustion chamber and ignite while atomized.

A fuel knock can be unnerving and sound much more serious than it often is. A rod knock is more of a pounding down low in the block, and likely develops over time to become gradually louder. But all bets are off with the use of ether! I've seen broken pistons, rings, and crankshafts that resulted from ether. One man's "small" squirt is another man's flood. If you absolutely must use ether, and I mean absolutely! Just give the engine enough to smell it. That's all! No liquid! Just the scent of ether does the trick. More and you are likely causing damaged ring lands and future compression loss, or worse.

But I have to draw the line at praying for a fix. Doesn't the Lord you pray to have better things to do than take care of your tractor? And, If I was him, I'd point out that you have been deliberately hurting your engine with ether and likely caused some damage yourself.

Cracking a line and quieting a noise does not always mean it is an injector problem. That also unloads the bearings. It can help narrow it down to a particular cylinder and is a good troubleshooting step.

I do agree on ether. Bad juju.

 

[Jerry/MT]

Sounds like you got the problem resolved. Good.

Second, idling diesels do not fire prematurely from hot carbon.

They can IF the injector is leaking.

 

[Raspy]

They can IF the injector is leaking.

Mechanical injection systems only send pressure to the injectors when it's time to inject. They have no or almost no pressure until then. When the injection pump sends pressure, it's time to fire and not early. All fuel is burned and there is nothing to fire until the next injection event.

Idling diesels have a hard time warming up because they have so much excess air being pumped through them. This means a cool combustion chamber and no glowing carbon sitting around to fire fuel that hasn't even arrived yet.

If these engines can sit without running and have an electric transfer pump running and bad injectors, they can slowly leak and hydraulic a cylinder, but otherwise run just fine even with a severely reduced pop point or a plain old leak. There is just not enough pressure to cause enough fuel to leak past a bad injector, between injection events, to be ignited early enough, in an idling engine, to be a loud knock. This theoretical situation just doesn't exist in the engine in question, that started up cold and knocked. His problem was about loose carbon, or a broken glow plug tip or poor atomization. Not hot glowing carbon in 25 degree startup.

High pressure common rail injection systems have very high pressure at the injectors all the time and can fail differently.

 

[Jbrink64]

Perhaps the man upstairs was making the noise to wake you up. Glad the noise went away.

On a mechanical fuel system, a leaky injector will affect timing. At the end of injection, the nozzle will close and hold pressure (just below cracking pressure) for almost 15 seconds.

Back at the injection pump, each pumping unit has a delivery check valve mounted just above the plunger. The idea is to maintain a near cracking pressure in the injector-fuel line-upper pump chamber until the next injection phase.

When an injector leaks, three scenarios happen.
1) a small amount of fuel dribbles into the pre-combustion chamber. This fuel smolders, and burns unevenly. Also causes soot.
2) the pump plunger needs to travel farther to bring the injector-fuel line-upper pump chamber up to the cracking pressure, causing the point of injection to be late.
3) a small amount of combustion gases (exhaust) during the power stroke, or air during the compression stroke, can be pushed back into the injector. This acts like having air in the fuel system, and further complicates timing.

I would definitely have the injectors tested for opening pressure, and leakage.

 

[OldBulldogger]

Thanks again everyone for the input. Seeing how I just got this tractor, I am in the process of changing out all the fluids and filters to establish a baseline for myself. One question I have is regarding the product SeaFoam. I have read where adding this to the oil is beneficial for many reasons. I would like to get your perspective on this. Also, my manual says to add 4.8 quarts of oil with a filter change. My question is this, to you add the Sea Foam in addition to the 4.8 quarts already in or do you cut back the oil appropriate to the amount of Seafoam ounces added so as not to over-fill?

I will look into the injectors as well being the one cyclinder had quite a bit more soot than the others.

 

[MD09]

One thing I completely overlooked... The#2 cylinder is sooted up, you changed the glow plugs I assume because it was hard to start. The soot in the #2 cylinder is most likely from a malfunctioning Glow Plug.

 

[Caliche]

Originally Posted by Raspy

"But I have to draw the line at praying for a fix. Doesn't the Lord you pray to have better things to do than take care of your tractor? And, If I was him, I'd point out that you have been deliberately hurting your engine with ether and likely caused some damage yourself. "


If your favorite son's tractor was broken and asked you for help, would you tell him you were busy with more important issues?

 

[Raspy]

Caliche,
I don't want to pop your bubble, but I'm not the Lord and have never claimed to be. I spend a lot of my time helping my family, my friends, my neighbors, my relatives and my customers. Always have and always will. I also take responsibility for myself and don't pray for favors from the Lord for tractor issues or any other little inconvenience that life brings. Or, maybe it would be better said that, the Lord helps those that help themselves, or why sit around praying when you can do a simple analysis of the problem and solve it yourself using the God given common sense that most of us have for that specific reason.

It's a matter of taking responsibility for ones self.

Someone that gets up and approaches a problem they are having, with their tractor for instance, with a wrench and some thought, will always do better than someone who simply sits and prays for the problem to go away or be fixed by divine intervention. Are you confused about that?

 

[Jerry/MT]

Mechanical injection systems only send pressure to the injectors when it's time to inject. They have no or almost no pressure until then. When the injection pump sends pressure, it's time to fire and not early. All fuel is burned and there is nothing to fire until the next injection event.

Idling diesels have a hard time warming up because they have so much excess air being pumped through them. This means a cool combustion chamber and no glowing carbon sitting around to fire fuel that hasn't even arrived yet.

If these engines can sit without running and have an electric transfer pump running and bad injectors, they can slowly leak and hydraulic a cylinder, but otherwise run just fine even with a severely reduced pop point or a plain old leak. There is just not enough pressure to cause enough fuel to leak past a bad injector, between injection events, to be ignited early enough, in an idling engine, to be a loud knock. This theoretical situation just doesn't exist in the engine in question, that started up cold and knocked. His problem was about loose carbon, or a broken glow plug tip or poor atomization. Not hot glowing carbon in 25 degree startup.

High pressure common rail injection systems have very high pressure at the injectors all the time and can fail differently.

Idling diesels do have a hard time warming up for the reasons you stated, However cold is a relative term. The peak gas temperatures in the cylinder just due to compression (CR=17) are on the order of 900F. It's even hotter when you add idle fuel. Not nearly as hot as when running at power but certainly> 900F is a tad warmish.

As far as the pressure across the injector, I think you'll find that the injectors are pressurized and they can and do leak fuel if they are worn or dirty and do not seal properly. If it was direct injection diesel, you can burn a hole in the piston from an injector leak.

 

[Raspy]

Burning a hole in a piston from an injector leak, or missing tip, is because of a jet off fuel rather than the designed spray pattern. it's a common problem, but not the problem being discussed in this thread. The correct spray pattern is very important for proper combustion.

Your theory that 900 degrees is enough to warm an engine misses the point. Its not the instantaneous temperature the combustion chamber reaches, it's the BTUs delivered to the block. Diesels have, whether you like it or not, a lot of excess air pumping through them all the time at light loads or while idling. This makes them hard to warm up in cold weather while idling. And they are not likely to have glowing carbon standing by at cold startup to prematurely fire the fuel that isn't even there yet, unless there is some kind of serious malfunction.

Please, no need to argue a silly point. Old bulldogger simply asked why it would be knocking at cold startup, at 25 degrees. All BEFORE it had time to warm up.