Cummins 855 - Low Fuel Pressure

[mathura]

This is a Cummins 855 Engine 350HP that runs a gen set. It works with a woodward electric govenor and actuator.

The probelm is that the engine hunts when running, tried another control and actuator and no improvement. I decided to check the fuel pressure and pressure is 10psi, according to the specs this pressure should be 100-120psi.

Replaced fuel filters and even tried it with a direct line to the pump but no improvement. Sent the pump to the fuel injection shop and still having the same probelm. I personally went to the fuel pump shop and saw the pump making 175 psi on the test bench.

Now what else I may be overlooking that is causing the low fuel pressure.

Thanks for your suggestions

[ddmech]

Injector seals is probably the issue.I have ran into that more than once over the years Mathura.Good luck.

[mathura]

Injector seals is probably the issue.I have ran into that more than once over the years Mathura.Good luck.


Thanks ddmech but thats the last thing I would like to check . pulling injectors.
Any other ideas from this this great forum

How do we verify injector seals without removal of injectors

Suggestions are appreciated

Thanks

[ddmech]

I hate to say it but after checking the pump and no problems the injectors and seals are about all that is left on an 855.You can take your pressure and bypassline off at the back of the head,pressure the lower fiting I beleive and see how much bypass air you get with the engine off.If you you get much a flow at all the seals are probably blown.I should be the middle seal that will be bad.I used to work on those things every day years ago.Kinda old and rusty on them,LOL.Hope this help buddy.

[Poptest]

Pump could be pulling in air. Use Cummins liquid eye tool to see for air bubbles. Disconnect suction hose from filter and let the PT pump pull fuel from a pail.

Check the 3/8 npt plug on top/front of PT pump. Pump will pull in air if this is loose.

[mathura]

I hate to say it but after checking the pump and no problems the injectors and seals are about all that is left on an 855.You can take your pressure and bypassline off at the back of the head,pressure the lower fiting I beleive and see how much bypass air you get with the engine off.If you you get much a flow at all the seals are probably blown.I should be the middle seal that will be bad.I used to work on those things every day years ago.Kinda old and rusty on them,LOL.Hope this help buddy.

Well while engine runs a lot of air is coming back through the return, but the return is connected to the upper port of the head and supply to the lower port.

No air from suction 100 % certain

[ddmech]

That is the way they should be.If you are getting air from the return line,it is probably compression leaking by the injector and getting into the fuel system.

[mathura]

That is the way they should be.If you are getting air from the return line,it is probably compression leaking by the injector and getting into the fuel system.

Ok My main concern is low fuel pressure at this time, should I pull injectors and check seals

[ddmech]

That was the point I was trying to make Mathra.If the injector is leaking compression into the fuel system, that is another sign you have a problem with the seals.Just my opinion,but I would definatly pull the injectors and check the seals.Ive had this problem many times in years past.S60 detroits are more prone to do it than the cummins.

[mathura]

That was the point I was trying to make Mathra.If the injector is leaking compression into the fuel system, that is another sign you have a problem with the seals.Just my opinion,but I would definatly pull the injectors and check the seals.Ive had this problem many times in years past.S60 detroits are more prone to do it than the cummins.


Ok ddmech, will let you know the results when I work on it

Thanks

[ddmech]

Just hope it helps friend,good luck.

[mang5087]

Ok My main concern is low fuel pressure at this time, should I pull injectors and check seals

you can also attach balloons to In & Out fuel lines,
and that will tell you if compression is entering fuel
system. it worked for me.

[mathura]

you can also attach balloons to In & Out fuel lines,
and that will tell you if compression is entering fuel
system. it worked for me.

Not sure how to do that, can you explain because I will be on that job sometime today

[Poptest]

Try this mathura. Disconnect discharge hose/pipe from PT pump shutdown valve. Connect a temporary hose to shutdown valve and immerse the other end in pail of diesel. Crank engine and check for air bubbles. Pump is pulling in air if you see bubbles.

Next, reconnect the original hose/pipe to the shutdown valve. Connect temporary hose to fuel return port on cylinder head and immerse the other end in diesel fuel. Start the engine......you will see some bubbles; this is normal. Too much bubbles means injector body seals are damaged.

Good luck....

[mang5087]

Not sure how to do that, can you explain because I will be on that job sometime today

loosen injector adj screws,
disconnect fuel solenoid wire.
disconnect fuel line at solenoid
and attach balloon to fuel line.
attach second balloon to return
line. crank the engine over if the
balloons start to inflate, one or
more injectors are leaking.
Poptest way maybe better for you
than this way.

[hanzem evr]

Hi friends

Please any body share service manual for nta 855 ???

[mathura]

Hi friends

Please any body share service manual for nta 855 ???

Here is the Nt 855 shop manual and gentlemen probelm solved by replacing injector seals.

[Poptest]

Here is the Nt 855 shop manual and gentlemen probelm solved by replacing injector seals.

Thanks for the update mathura. We learn when fixes are posted.

[ddmech]

Didnt even know I was a cummins mechanic!LOL!
Have a good one brother.

[hanzem evr]

Here is the Nt 855 shop manual and gentlemen probelm solved by replacing injector seals.

this is not same type, i need the oil pressured injectors

thanks a lot for help

[Poptest]

this is not same type, i need the oil pressured injectors

thanks a lot for help

These are STC (step timing control) injectors, often used on N14 engines. It is possible that the manual you need is posted on ZDS' thread.

[mathura]

These are STC (step timing control) injectors, often used on N14 engines. It is possible that the manual you need is posted on ZDS' thread.
I am not sure what our good friend is looking for

[spannermonkey]

he is looking for manuals for new big IV, 88NT, N14 mechanical with STC i think. I have hard copies of the manuals at home but not electronic