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756 injector question


pt756
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hello again, on our 756 d 310 diesel we think one injector is not quite right, at a idle it makes kind of a hiss sound, however it runs fine at higher rpms, i know very little about the injector repair, well nothing really, not a lot of d 310 mechanics around here, dealer did show that it is cone shaped, is there some kind of washer or seal at the bottom?  i wlll be taking it somewhere to get repaired, also what about injector lines, some one said on here last fall when i asked that one of the parts suppliers has them new? thanks for the help

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How are you determining that a specific injector is making this hiss noise? That just doesn't seem like something you can stand next to the engine and listen for. I know I'll hear an engine clattering away like it's going to come apart, and others will say, "Listen to that baby purr! Smoooooooooth!" Then I'll hear an engine that sounds perfectly normal and everyone else around will say, "Ooooooh listen to that massive rod knock. She's not long for this world." I just can't figure out how a normal human could pick out a hiss among all the other noise that's going on.

There were several answers to your question about injector lines in the thread you started the other day. Just in case you forgot that you posted that thread:

 

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23 minutes ago, Matt Kirsch said:

I just can't figure out how a normal human could pick out a hiss among all the other noise that's going on.

I can usually pick out noises like that, if my failing hearing can pick them out, but I agree most people can't hear a major problem and tell the difference between it and a minor one.  Unless it is really bad, I don't know how the OP could determine it to be a specific injector.  Usually you have to use soapy water to find an injector leaking compression.  I would suggest doing that before pulling any injectors. 

As for the point about not being any 310 mechanics around.... a shop that is good with diesel engines should have no issue working on one. 

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Another thing to consider; is the check valve that goes into the bottom of the fuel tank partially plugged?

Over the years, I worked on two German diesels that ran great at high idle, but crappy at low idle.  I found that at high idle, the tractor was burning up enough of the fuel pumped to the injectors, but at low idle, because of the need to bypass more of the fuel back to the tank, it was causing back-pressure on the pump or injectors.  

This would be easy to check.  Just remove the excess fuel line connection leading to the tank and divert the excess fuel into a container and see if the tractor runs good then.

 

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I’m kinda spit balling here but you *could* have a head gasket leak.  The sound that makes can be a hiss or a “chiff” in the exhaust note and it can tend to go away as the engine speed goes up.

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17 hours ago, pt756 said:

hello again, on our 756 d 310 diesel we think one injector is not quite right, at a idle it makes kind of a hiss sound, however it runs fine at higher rpms, i know very little about the injector repair, well nothing really, not a lot of d 310 mechanics around here, dealer did show that it is cone shaped, is there some kind of washer or seal at the bottom?  i wlll be taking it somewhere to get repaired, also what about injector lines, some one said on here last fall when i asked that one of the parts suppliers has them new? thanks for the help

There are no sealing washers under the injectors on those engines. Get in there with a brush of some type and clean it out and clean the injector taper and try it again.  Other wise the injector sleeve may need to be replaced if it's pitted or something. 

 

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Hisses and what you described are usually due to a valve not sealing as it should.

Compression is being leaked back into the intake or exhaust stream.

I would first remove all the nozzles and have them tested for break pressure, dribble, etc..

While out, do a compression test, if you can get the nozzle adapter and gauge to do so.

Most diesel shops can do this for you.

Also check the pump timing to be sure it is correct.

A general tune-up may get this running back the way it should.

 

 

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