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Old 18-11-2011, 17:52   #1
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Fuel Delivery and Injector Pump

I,posted yesterday and received some valuable info,Now today I,spoke with the tect ,he said he beleived he had good compression but still no RPM output beyond 1500 RPM's.Talked about fuel lines possibably have air or something to that effect.I always beleived that any air in a diesel system would shut it down or prevent it from running.Also he stated the injector pump my not be good out of time or something to that effect,I,wonder how does that happen,I am on a learing curve,thisn Yanmar sounds complicated,compared to my Universal.Thanks again folks for the replys.

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Old 19-11-2011, 09:35   #2
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Re: Fuel Delivery and Injector Pump

Firstly- air is 100000% necessary in all internal combustion engines. What you said is actually the opposite of whats true; NO ICE (Internal Combustion Engine) will work without air (including petrol, diesel, biodiesel, oil combustion, hydrogen atom, etc. etc.), the air is the fuel for the combustion, and the diesel/petrol/whatever is the trigger to the combustion.

And to understand how a "injector pump" may not be good, we must first understand the basis of how diesel engines work.

Very simply, in its essence of terms, it works like this.

1] Air comes in from the intake when the piston lowers itself (creating a sucking vacuum of air)
2] The piston moves up, compressing the air GREATLY, heating the air up very quickly and intensely; the moment the air is at its maximum compression rate, diesel is shot into the cylinder. This makes an extremely large explosion, because diesel is very sensitive and volatile to heat, and since the air is heated greatly, it explodes only milliseconds after injection, causing a large, powerful stroke to the crankshaft.
3] Exhaust gases form from the explosion, rushing the piston down into the crankshaft, this is called the "power stroke" as it is the only stroke that actually helps move the engine instead of steal power from it.
4] The piston moves up again, expelling the burned air out the exhaust, and then readies itself for the cycle to begin again.

Now, in stroke two, the fuel pump needs to be perfectly in sync with the computer, if it is even slightly off, or the pump is even a little weak, the whole diesel engine becomes very weak (since if you inject diesel when compression is very low, it may only cause a very weak explosion, or NONE AT ALL), and if this is happening to every cylinder constantly, then the engine may halt, or produce very low output power.

Any other questions?

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Old 19-11-2011, 10:23   #3
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Re: Fuel Delivery and Injector Pump

I think the original post was referring to air in the diesel fuel lines as a potential cause for his problems, not referring to the air that feeds the combustion. Air in the fuel lines is absolutely a problem and can give all sorts of symptoms from not firing at all, RPM surging up and down and probably others. I guess it is possible but I do not think air in the fuel lines would allow the engine to run smoothly but limit the max RPM. To me that sounds more like lack of diesel fuel, probably due to some restriction in the fuel line somewhere. Might be from a faulty fuel lift pump.

Now if you want to be nit picky (sorry I just can't help it), it is quite correct that air (or more specifically the 20.9% oxygen in the air) is necessary for combustion but the oxygen is not the fuel. The diesel is the actual fuel, the part of the process that contains the energy, burns as an exothermic reaction and releases that energy in the form of heat. The oxygen supports the combustion or oxidation process but is not the fuel.

And there are also 2 stroke diesels as well as the 4 stroke you describe.
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Old 19-11-2011, 10:27   #4
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Re: Fuel Delivery and Injector Pump

We need to refer to the other thread for info about the motor. Yanmar Lack of Power

The injector pump can get out of align by the adjustment coming loose, worn gears or gears loose in the shafts.
As for air in the lines, it can come in thru loose hoses or fittings (suction).

You could try running a line into a fuel can right from the lift pump, making sure the fittings up to the pump are secure. If it still runs slow then that eliminates the air possibility.

And have you eliminated the trany as a possible problem?

Blocked air ways, restricted fuel filter up-line from the lift pump, restricted exhaust or even a stuck throttle can be added to the list of possibilities.
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Old 19-11-2011, 11:20   #5
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Re: Fuel Delivery and Injector Pump

Thank you all again,Yes I was referring to air in the fuel lines,I do NOT profess to be a Tect,but need to learn more I read tec datta on the net and it is not always clear,You folks explain it a lot better.Regarding injector pumps at 2000 hours or so on an Yanmar diesel would you expect wear to the degree that would create this problem?The tect up north has been going thru a process of elimination ,I found an article or service bulliten from Yanmar regarding the engin stating the lift pump connection to the engin may be sucking air in some instances,they provided new fittings,I passed this on to the tect up North.The injector pump thing has me curious as to the actual hours I was quoted 1600,that is my curosity as to injector pump wear.
To the First posting Gentelman,I have your boat waiting if this new one comes together C&C 36 Centerboard M 4 30 Universal diesel 900 original hours installed by me and my son clean Bahama ready,Won't sell till other deal gets done,be lost without a boat to mess with.Take Care All and Thanks again
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delivery, fuel, fuel pump, injector pump

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