L10 Cummins. -one day good oil pressure and next day extremely low ISSUE

[mwilson]

Give me the ESN and I’ll post some illustrations for you..

 

[Nathaniel McClain]

Don't have a store but maybe If I could figure out how to upload pictures I could help,and i think you can go to cummins insite and find what you need

I checked over everywhere only thing I can pull is a diagram for parts list. I even did a ticket with them to help but they had nothing to offer.

 

[Nathaniel McClain]

Give me the ESN and I’ll post some illustrations for you..

Thank you! It’s 34688525

Thanks again

 

[Nathaniel McClain]

X2 Double check the pressure. Many engines/transmissions have been needlessly removed and overhauled over bad (pressure/temp) gauges...

Does the oil smell like diesel fuel? I assume it's at the marks on the dipstick not over or under level. Do you do oil samples on this engine? Now is the time to send a sample in (even if you don't do samples). Chasing a problem like low oil pressure is best to have a sample rather than just dumping the oil for fresh oil. The sample can give you some clues as to oil contamination coolant/dirt/diesel. Viscosity could have thinned out due to contamination and an oil sample will show this. (Oddly oil samples don't report Biodiesel contamination as "fuel in oil" but will show low viscosity.) Further a sample can show you extreme metal or soot indicating a failure is happening before you ventilate the block.

If you do change the oil it's also a good idea to cut the old oil filter open and see if you can read part numbers in metal debris. Hopefully not. You do not have to change the oil to check just the filter.

I did an oil change immediately when it started and haven’t driven much jsut in testing. Worth puking filter and testing again?
It’s an old engine and burns oil but we keep it a good level daily. It really runs good when it’s a “good” day. I love this engines power. When the issue happens, it tends to smoke a lot so I’m pretty confident that it’s just not gauges but I’m going ti check them personally as only my mechanic did before just to make sure

 

[Wayne M.]

Well that’s a good clue, that it runs worse when the pressure drops.
I don’t think the oil pressure has any bearing on this fuel system, like a HEUI would. In fact I think this engine is one of the last Cummins PT systems.

 

[mwilson]

Looks like it has STC...(step timing control)....

 

[Nathaniel McClain]

Looks like it has STC...(step timing control)....

I’ve read about it but but that it would effect the oil pressure that drastically. But I literally only know what I’ve read

I’ll look into that further

I’m also going to check/ replace the bypass and see it that is potentially sticking.

Thanks for the help. I’ll keep everyone updated to what I find so maybe it can help someone else with same issue

 

[Tuesdak]

Any other history like recent repairs? Has anyone checked the turbo for the source of burning oil? Edit: from the pics it may be leaking oil not just burning it. And how much does it burn anyways?

Low engine RPM when running bad?

The fresh filter may not tell you anything. Oil samples need around 1000 miles and that is even low miles to see much.

 

[Wayne M.]

When the issue happens, it tends to smoke a lot

Does this engine have STC? And is the smoke white?

 

[JR]

Looks like it has STC...(step timing control)....

Bingo. I thought about this last night and dug up some info but decided not to post it because the OP didn't mention any physical changes in engine op.

Here is a description of the system, from Cummins.

Refer to Step Timing Control Familiarization, Bulletin 3387380, for addition information on STC.


STC has two stages of injection timing. The engine operates in the ADVANCED mode of injection timing during starting and light engine load conditions and at NORMAL timing during medium to high engine load conditions.


STC offers many advantages. During ADVANCED injection timing, it:

•Improves cold weather idling characteristics
•Reduces cold weather white smoke
•Improves light load fuel economy
•Reduces injector carboning.


During NORMAL injection timing, STC:

•Controls cylinder pressures
•Reduces nitrogen oxide emissions.


The STC system consists primarily of:

•STC injectors
•STC oil control valve
•STC plumbing and check valve.
These components control injection timing based on fuel pump rail pressure (engine load).



In the injector, injection timing is controlled by the STC hydraulic tappet. The tappet has an inner piston (plunger) and an outer piston (sleeve). These tappet components work together with the injector plunger to control injection timing.



In NORMAL timing, no oil is in the tappet. As the cam follower starts up the camshaft injection ramp, the injector rocker lever begins to force the inner piston downward. Because no oil is in the tappet, the inner piston must make direct contact with the outer piston before the injector plunger can begin its downward travel.


In ADVANCED timing, the tappet is filled with oil and the injector is metering fuel. As the cam follower starts up the camshaft injection ramp, the injector lever begins to force the inner piston downward. Since the oil between the pistons forms a solid link, the downward pressure is immediately transmitted to the outer piston and the injector plunger begins its downward travel earlier than it does in NORMAL timing. This causes the fuel to be injected earlier.



Engine oil flows from the STC oil control valve through the oil manifold to the tappets. Whenever the oil pressure in the oil manifold exceeds 70 kPa [10 psi], it moves the tappet inlet check ball from its seat and fills the cavity between the inner and outer pistons.



During the injection cycle, the oil is held inside the tappet by the inlet check ball and the load cell check ball. When the rocker lever forces the inner piston downward, the solid link of oil causes the injector plunger to contact the fuel earlier; therefore, the injection timing is in the ADVANCED mode. At the end of the injection cycle, injection force increased the oil pressure in the tappet and holds the injector plunger firmly in the cup.


This increased pressure moves the load cell check ball from its seat. The oil drains past the load cell check ball and through the drain holes in the injector adapter and returns to the oil pan through drain passages in the cylinder head and block. Meanwhile, with continued cam lift, the inner piston makes mechanical contact with the outer piston and maintains injector plunger seating force.


The STC control valve uses fuel pressure and spring force to control the position of an AFC style plunger. The position of the plunger dictates whether the oil passage to the hydraulic tappets is open or closed. Fuel pressure acts on the piston end of the plunger.



During ADVANCED timing (low fuel pressure), the spring opposes the fuel pressure and holds the plunger in the open position. Pressurized lube oil flows to the tappets and initiates ADVANCED engine timing. As fuel pressure increases, the spring holds the plunger in the open position until the fuel pressure rises above the certified switching pressure.



At this certified level, the higher fuel pressure overcomes the spring. This action shifts the plunger and closes the oil passage. The oil supply to the tappets is interrupted and the engine begins to operate in the NORMAL timing mode.



The control valve supplies oil to the STC rocker housing connection through the STC valve oil outlet line (1).

A check valve in the elbow fitting (2) prevents the oil from draining back into the engine when it is shut off. This prevents any delay of oil to the tappets during cold starts.



An internal oil manifold connects the oil supply to each STC injector in the rocker housing.



Fuel pressure to the STC valve is provided by a hose (1) between the fuel inlet passages in the cylinder head and the STC valve. The internal spring cavity of the valve is vented to the engine crankcase by the crankcase vent line (2) in order to allow the plunger to cycle freely.


The oil control valve is calibrated to a specific flow and pressure using a fuel pump test stand. Tampering with the valve or plumbing will result in the loss of both fuel economy and engine durability. Correct valve operation is necessary to maintain acceptable cylinder pressures and white smoke levels and to assure optimum fuel economy.

 

[mwilson]

Oil Cooler...

 

[mwilson]

Parts list..

 

[mwilson]

I watched my father (who is a top shelf diesel tech) struggle with STC, trying to remember if one of those tappets or the oil control system can cause these symptoms....

 

[Wayne M.]

I was real wrong about oil pressure and timing not being related. It is. I have a booklet in front of me that I dug out of the shop archives.

 

[Wayne M.]

Here’s a description.

 

[Nathaniel McClain]

I was real wrong about oil pressure and timing not being related. It is. I have a booklet in front of me that I dug out of the shop archives.

Awesome I’m going to check this for sure.

Thanks for the diagram! I’m going to check this this week too

 

[TFucili]

I am surprised to find this monkey business on an engine of that vintage.

 

[Wayne M.]

I am surprised to find this monkey business on an engine of that vintage.

Agree.
I thought Celect was the first real effort at smoke control.

 

[Nathaniel McClain]

Putting this all together in my mind... I’m thinking oil bypass could be dropping oil pressure and this is messing up stc timing which is why it smokes white on the “bad days”

It makes sense to me. Any thoughts to that?

Here’s a description.

View attachment 114441 View attachment 114442

 

[mwilson]

Putting this all together in my mind... I’m thinking oil bypass could be dropping oil pressure and this is messing up stc timing which is why it smokes white on the “bad days”

It makes sense to me. Any thoughts to that?

That's my train of thought as well.

I would....

(1) Verify the oil pressure gauge operation using a test gauge.

(2) If gauge test backs up the existing gauge readings see if the skipping and low oil pressure coincide. But an issue with the oil pressure due to bypass valve or other issues may cause the STC distress, or vice versa...I don't envy you on this one......

(3) Order or borrow a printed manual specific to the CPL of your engine. It's not on Quickserve as you discovered...but you can order it from Cummins...