Yanmar 3TN72 Injector Pump

[Tater50]

I am on a JD 756 (755) project that has a 3TN72 (think I am right) and it was sitting for many years.
1. Removed tank & ALL lines & fuel filter & installed a new fuel pump. I have fuel coming out of fuel bleed screw where it attaches to IP.
2. When I start engine: fuel shutoff solenoid (New) is working fine; I can get fuel coming out of each connector @ injector; but it does not have a lot of PSI; but still is coming out w/similar PSI that I viewed when I bleed my JD955.
3. I cannot get it to start. I see some bubbles; do this engines take a while to bleed?
I thought there may be some sort of manual pump to use to force it out at the injector connections; but I did not see one. I am not familiar w/the Yanmar; so any ideas or pics would be appreciated.

 

[Dieseltech]

The smaller diesel injection pumps can take awhile to bleed, as even when set to full load fuel delivery, VERY LITTLE fuel is delivered to injectors. If engine has glow plugs, remove them all so engine will crank easier/faster with all injector lines loose at INJECTORS, NOT THE PUMP!! When you see air free fuel at each injector tighten the lines. Now crank engine until you see air/fuel mist blow out each glow plug hole, this means pump is opening injectors and fuel is entering the chamber. Now install the plugs and engine should start easily. It still may take awhile even using this method, so let the starter cool a bit between tries as needed.

 

[Tater50]

No glow plugs. I have doing it wrong. I loosen 1 line @ injector; turn engine over; retighten & go to the next. So; I will give it a go tomorrow. Thank you very much.

 

[Tater50]

BTW: I have clear return lines from injector to injector; shouldn't I see some fuel in those lines as I am cranking? Maybe; they only return when pressure has reached a certain PSI?

 

[Dieseltech]

The injector leak off lines have VERY LITTLE fuel from injectors going back to the tank. If the injection pump is also connected you might see more from it than injectors. I'd have all lines loose at injectors, and throttle set 1/2 half open. Those small engines can take awhile because so little fuel is pumped to the injectors anyway. Also, MAKE SURE the pump outlets are tight where injection lines attach, torque to 25 FT/LB if any are loose. If any ARE loose pump will never deliver fuel correctly, fuel will bypass from high pressure side back to gallery/feed side keeping pump from working. Best to ALWAYS bleed those lines at injectors, NOT the pump so those fittings stay tight.

 

[Mike M]

I had a 755 and those are a real pain to bleed out. I ran mine out of fuel twice. The pick up tube must not of went into the tank very far as it would run out with a decent amount of fuel in it. So make sure you top off the tank first. I had to bleed the pump and then loosen all lines up at the injectors until fuel dribbled out at them. Then tighten up the lines and it would then start.

 

[MSM]

3tn72 should have glow plugs

 

[Tater50]

I was"totally" wrong; it does have glow plugs & looking at the age; there are probably bad. Do I need to replace them before trying to start?

 

[Mike M]

Test to see if they are getting any voltage.

 

[Tater50]

Getting power to Glow Plugs. WOW!!! I am getting old & not reading clearly. "From DieselTech: Now crank engine until you see air/fuel mist blow out each glow plug hole, this means pump is opening injectors and fuel is entering the chamber. Now install the plugs and engine should start easily." I did not follow this procedure; but will tomorrow when I tinker some more. Thanks to all the replies!!

 

[Dieseltech]

I hook each glow plug to a 12V battery charger, ground at the thread area and plus to the terminal end. Turn on the charger and watch the tip end, it SHOULD heat up in a few seconds, STOP the charger when tip just starts glowing red. If they all heat up like that they are OK, if any don't heat up at all, or don't start glowing red that one is bad.

 

[Tater50]

Thanks; I will proceed w/that today. I sprayed some blaster around the top; going to blow that off & hope that they can be removed w/o any breakage!!

 

[Tater50]

(quoted from post at 15:05:12 12/22/19) The smaller diesel injection pumps can take awhile to bleed, as even when set to full load fuel delivery, VERY LITTLE fuel is delivered to injectors. If engine has glow plugs, remove them all so engine will crank easier/faster with all injector lines loose at INJECTORS, NOT THE PUMP!! When you see air free fuel at each injector tighten the lines. Now crank engine until you see air/fuel mist blow out each glow plug hole, this means pump is opening injectors and fuel is entering the chamber. Now install the plugs and engine should start easily. It still may take awhile even using this method, so let the starter cool a bit between tries as needed.

1. I removed glow plugs; bench tested; they were bad
2. Loosened all 3 connectors @ injectors & turned engine 7 times for 10 seconds w/a rest period.
3. Retighted all 3 connectors @ injectors.
4. Turned engine over 4 different times for a period of 5+ seconds & mist was shooting out the glow plug holes
5. Installed NEW glow plugs (tested before installation) & made sure 12V was going to each glow plug.
6. Cranked engine 5+ times for a period of 10 seconds w/a rest in between.
7. I got NO start; did not even hit; not once. I put my hand over the air intake hole & could feel a good suction. I have read "not" to spray ether; so I am going to bypass that!!
Now; you have helped me greatly to this point; what should I do next? I have "never" checked compression on a diesel; so I am at a loss on that. Thanks BTW; this is an OLD JD; so the engine could be shot!!

 

[Tater50]

According to my search: I have to remove injectors to test compression like a spark plug on a gas engine; but I'd have to buy or rent the tester; so I am going to listen to you guys first to see if I may have missed something!! Thanks!

 

[Bob]

(quoted from post at 15:58:45 12/29/19) According to my search: I have to remove injectors to test compression like a spark plug on a gas engine; but I'd have to buy or rent the tester; so I am going to listen to you guys first to see if I may have missed something!! Thanks!

NOT sure what you've got going on, since it is apparently injecting fuel, as you say you had fuel mist puffing out the g.p. ports.


It seems very unlikely that all the cylinders would be so low on compression it won't fire or at least smoke IF the glowplugs are actually heating up. Are you SURE they are getting power/heating?

Any chance the engine has been apart and someone has messed up the camshaft timing, which would also throw off the injection timing?

At this point, I'd disconnect the glowplug power, then try a TINY puff of starting fluid and note if it starts, or at least fires.

If no luck and you need to check compression, it can be checked though the glowplug ports with the proper adapter.

As to a diesel compression tester, an adequate/function diesel compression tester can be had fairly reasonably through Amazon or ebay, and HOPEFULLY come with a glowplug port adapter that will fit the Yanmar head.

 

[Tater50]

(quoted from post at 14:41:47 12/29/19)

(quoted from post at 15:58:45 12/29/19) According to my search: I have to remove injectors to test compression like a spark plug on a gas engine; but I'd have to buy or rent the tester; so I am going to listen to you guys first to see if I may have missed something!! Thanks!

NOT sure what you've got going on, since it is apparently injecting fuel, as you say you had fuel mist puffing out the g.p. ports.


It seems very unlikely that all the cylinders would be so low on compression it won't fire or at least smoke IF the glowplugs are actually heating up. Are you SURE they are getting power/heating?

Any chance the engine has been apart and someone has messed up the camshaft timing, which would also throw off the injection timing?

At this point, I'd disconnect the glowplug power, then try a TINY puff of starting fluid and note if it starts, or at least fires.

If no luck and you need to check compression, it can be checked though the glowplug ports with the proper adapter.

As to a diesel compression tester, an adequate/function diesel compression tester can be had fairly reasonably through Amazon or ebay, and HOPEFULLY come with a glowplug port adapter that will fit the Yanmar head.

I bench tested the Glow Plugs & tested the power to each one.
This JD was owned by Ga Government; then sold to an individual that I bought it from; so I have no clue as to what has been replaced. etc. I will try the tiny ether spray. GLAD you said to unplug glow plugs; I would not have thought of that.
My logic was like yours; I did not think that ALL cylinders would not have some compression. Will give it a go tomorrow & get back to you on the results. Thanks

 

[Tater50]

Bob wrote "I'd disconnect the glowplug power, then try a TINY puff of starting fluid and note if it starts, or at least fires."
I just tried this; w/glow plugs unwired; I sprayed 1 quick spray of ether & turned engine over. I could tell that it was trying to compress the ether by a partial revolution, but after that is what regular starting. It did not fire at all. I guess next step is to check the compression. This is a project JD, not a 911; so I will be patient; probably something simple & I am also learning a lot!!

 

[Tater50]

If the rings are stuck, can I pour some Marvel Mystery Oil or another suitable product into the intake & let it sit for a couple of days to see if they will unstick? Just a thought!!