Believe it or not, this is the third time I am attempting to write and post this. I typed for ages this morning and upon htiing Submit, something went wrong my end and I
lost it all. I came home this evening and did it all again. This time, something else hapend and I
lost it all again. OK, third time lucky, or no one will ever see this, and of course, you will never even know.
OK, firstly Rick, the best thing you can do is to get those things serviced. Well worth the effort. Here's some info that will explain why and hopefully help some others in diagnostics.
An injector is a high precision piece of engineering, being asked to operate in an extremely harsh
environment. They have a duty cycle that requires them to be serviced once in awhile. This is ruffly every 1000hrs. Although they will often
work just fine for many tens of thousands of hrs with seemingly no adverse effects. Seemingly!
How it all works. Well it's reletively simple actually. The injector comprises of a needle valve and a seat. Both highly precision ground and polished. Behind those is a spring. The
injector pump provides a metered dose of fuel at a substantial pressure to the injector. As the pressure reaches a threshold, the pressure overcomes the force of the spring and the needle is lifted and the dose of fuel is sprayed into the cylinder.
Because of heat and the fact that the spring is always under tension, the spring slowly looses strength and this is mainly what needs to be adjusted every 1000hrs or so.
The needle and seat can be damaged very easily. Water is the biggest enemy of these two. The main way water damages an injector, is
corrosion and contaminants being left behind in the internals as the water boils away. The seat is higly polished and very precise and
corrosion on the seat surface effectively destroys it's ability to
work as it should. The other major
danger, is the fact that water will instantly expand to 700 times it volume when boiled. As soon as it reaches the tip, the extreme temperature causes it to explode and it can damage and even chip the nozzle tip.
At this point, I want to bring in some info on fuel additives. Be careful what is in them. The Base products of some are nothing more than Kerosene. Kero is a very good cleaner but it has a very major negative. It is very abrasive. It does not lubricate metal
parts very well. So be very careful at what you run through the fuel system in any concentrated form. The other point with additives, is the way in which they handle contaminants in the fuel system. There appears to be two basic ways of doing the job. One is to mix water with the fuel so as it burns away and the other is to seperate any water and moisture out of the fule so as it can be trapped in the filter system.
The ones that emulsify and mix the water in, need to be viewed with caution. You CAN NOT turn water into fuel. Trust me, many have tried, no one has found that holy grail yet and the one that does, will be a rich man indeed. So water, in what ever form, entering the injector, can cause damage. In saying that, I do use a product Talbot described, called Fuelset. I watch my seperators on a regular basis to check for water, but I also use the fuelset in a "in case of" situation. Remember, when it goes wrong, it is going to be a very inopportune moment and I would rather have an injector damaged and get safely out of trouble, than to worry about an engine shutting down right when I don't want it to.
Now on to what to look for. Well, this part is a little tricky. It's easy to say, "Oh if you see such and such colour of smoke, this is the problem", but it isn't always as simple as that. So the following are some guide lines that hopefully could help.
To correctly diagnose an engine, there are some basic principles to use. This is befor you start ripping things apart and/or connecting up expensive test
equipment.
What is the complaint, what are the symptoms, what do you see and what do you hear.
The last two are VERY important. What is happening with the
exhaust smoke. Do you see anything unusual. Remember, just because it has smoke, doesn't mean it has a fault, it could be a
Volvo eh darryl
.
If it's your engine and you know it well, has the sound changed.
OK, before I go further, to follow on from the description at the begining of how things work, well take the stroy back up. The needle is lifted by the
pump pressure and as it lifts, the fine hole and shape of the seat, causes the fuel to atomise and spray out in a pattern. This pattern actually has the cylinder designed around it. You don't want fuel igniting on hot
parts of the engine. It will eventually burn those parts out, like pistons and valves etc. So if that spray pattern has been altered in anway due to a damaged seat, then it will not burn correctly. If the fule does not burn correctly, it will cause all sorts of issues in the engine.
A totaly blocked injector, will of course mean that that cylinder is not firing at all. Easy to spot so you would think. But because a diesel tends to run ruff, sometimes it is not so easy to spot. So you run down the injectors and lightly crack the fule rail nut on each top. This will drop the pressure enough to stop an injector from working if it was working to begine with. Listen for a change in the tuning condition of the engine.
A stuck open injector, never allows the fule pressure to rise enough to cause it to atomise. It squirts out in a jet and will can cause several problems. A common sign for this, is the engine will start fine cold, but be difficult to start hot. Normally seen when the engine is using a heat source like glow plugs. The heat source vaporises the fule at it starts fine and will run fine. Once the engine is hot, the heat source is no longer used and the squirt of fuel will not ignite when you try and start the engine. This can also be very bad, as it is
washing oil from the cyclinder walls and diluting the engine lubricant in the sump.
A damaged seat can cause the burn pattern to change. The burn pattern is important for two major reasons. the main benifit of diesel is the enormuse Torgue they can produce. This is from the slow rate the fuel burns at. It produces a long
power period over the length of the stroke. If the burn pattern is changed, so can the burn period or just simply, the
power that should be gained fromt he way the burn takes place, could be substantialy reduced.
The other issue is, the spray pattern ignites on hot components such as say an exhaust valve and can cause improper detonation timing, plus heat damage to those components.
To sum up, the major beuty of a Diesel is it's simplicity of operation and the fact that they are very reliable. The major disadvantage is, they are precision machines of extremely high tolerances.
Hope this wasnt a bore.
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