Help w/ Yanmar 3JH3 Power Drop-Off Mystery

[skipperpete]

I doubt that a measurable change in timing would occur with higher nozzle pop pressures, I seem to remember that the auto advance mechanism on your injector pump drive gear does that. I bought a “Snap on” diesel timing light a few years ago and found a whole new world of diesel diagnostics, and it saves a lot of time that I once invested in spill timing and checking auto advance mechanisms.

[skipperpete]

Are you having any positive results from your troubleshooting ?
Have you checked the tacho for accuracy? Your tach sender is close to the exhaust mixer elbow and can get dripped on by salt water. The iPhone tach apps work well enough to establish rpm error.

[kenbo]

I was just going to mention checking the tach accuracy as well. From memory, the continuous max rpm for the 3JH3E is 3650, not 2900 as the OP said was his max. Check the tach, check for exhaust back pressure (120" of H2O or 4.3 PSIG at 3800 rpm), feed the fuel pump clean fuel and lastly feed the secondary filter clean fuel by head pressure.

[Britishsea]

Originally Posted by skipperpete

Are you having any positive results from your troubleshooting ?
Have you checked the tacho for accuracy? Your tach sender is close to the exhaust mixer elbow and can get dripped on by salt water. The iPhone tach apps work well enough to establish rpm error.

Thxs for your input on the timing issue.

I was at the yanmar parts shop today and bought some a few items to try over the weekend. I have ordered a fuel bulb from Amazon and if its arrives on time, will do some investigation this weekend and report back to the Forum with results.

[Britishsea]

Originally Posted by kenbo

I was just going to mention checking the tach accuracy as well. From memory, the continuous max rpm for the 3JH3E is 3650, not 2900 as the OP said was his max. Check the tach, check for exhaust back pressure (120" of H2O or 4.3 PSIG at 3800 rpm), feed the fuel pump clean fuel and lastly feed the secondary filter clean fuel by head pressure.

I did have the tach checked a few years ago during a mechanical survey when I bought the boat.. It was reading 100 high at that time. I don't think it's too far off as i have gotten to know my engine by ear. I will check out the iphone apps. Did not know that was a thing.


Agreed that 2900 is low for this engine, but it never would go above that RPM level since i owned the boat. I thought I was over propped - but i bought a new prop a few years back and the manufacture (Flexofold) confirmed the i have the correct pitch and size for my boat, gear box and engine.

It's possible that whatever is causing this issue now has been around for a while and was restricting my top end RPM. I normally cruise btw 2200- 2600 RPM so has not been an issue for me till now.

I'll try to check the exhaust manifold pressure over the weekend and report back. However, if it was the exhaust, it should be restricted whether the engine is hot or cold.

I'm starting to wonder if i have a soft fuel line which when it gets hot, is collapsing under negative pressure.

[skipperpete]

Here are what Yanmar call the “considerations” for your engine. Loss of power can be difficult to diagnose so a good mechanic will establish a base line by quickly and progressively eliminating all the easy stuff before addressing the less obvious causes so
Check the disconnected movement of the throttle lever under power
Check accuracy of tacho.
Check air filter
..........all fuel filters.
..........valve clearances
..........parasitic loads
......... exhaust for smoke.
..........exh back pressure

Then move on to the “crack injector line nut” to check individual cylinders.
Consider a completely separate fuel supply from a 20 litre can in the cockpit
Check return line for bubbles.
This proceeds towards more serious interventions such as cylinder leakage test, timing and injector pump check and maybe remove the cylinder head if any other tests indicate that as a reasonable next step.

[Britishsea]

Originally Posted by skipperpete

Here are what Yanmar call the “considerations” for your engine. Loss of power can be difficult to diagnose so a good mechanic will establish a base line by quickly and progressively eliminating all the easy stuff before addressing the less obvious causes so
Check the disconnected movement of the throttle lever under power
Check accuracy of tacho.
Check air filter
..........all fuel filters.
..........valve clearances
..........parasitic loads
......... exhaust for smoke.
..........exh back pressure

Then move on to the “crack injector line nut” to check individual cylinders.
Consider a completely separate fuel supply from a 20 litre can in the cockpit
Check return line for bubbles.
This proceeds towards more serious interventions such as cylinder leakage test, timing and injector pump check and maybe remove the cylinder head if any other tests indicate that as a reasonable next step. Attachment 244040

Thxs Skipperpete. I especially like the note about checking the return line for air bubbles.

This engine comes with no air-filter, just a metal mesh filter. There is a metal box after the mesh filter with a wire attached to it. Presumably it's some kind of sensor (mass air flow? heat?). I have wondered if this could be a culprit.

Because my problem gets worse with engine heat, and there is no smoke and no overheat alarm, I am assuming that i can rule out air filters, exhaust pressure, valves, etc as these would present from cold.

Unfortunately , like many Yanmars of this generation, I only have an overheat alarm and no temp gauge. Have you found a good way to determine engine temperature with a thermometer? Or a way to put in an aftermarket temp gauge.? I tried a handheld laser temp gun on the heat exchanger, but got some erratic readings....

[skipperpete]

The metal box is the coldstart heating coil.

[Britishsea]

Originally Posted by skipperpete

The metal box is the coldstart heating coil.

Thxs for this bit of information.

I had no idea this was a pre-heater circuit. Is it activated manually? Or is there an automatic timer or thermostat?

[skipperpete]

That depends on which panel you have, on most its in the keyswitch .....rotate to the left and hold. Terminal G on the switch and should be a blue wire.
For the temp, shoot the temp switch or close to it on the front of the engine

[Britishsea]

Originally Posted by skipperpete

That depends on which panel you have, on most its in the keyswitch .....rotate to the left and hold. Terminal G on the switch and should be a blue wire.
For the temp, shoot the temp switch or close to it on the front of the engine

Skipperpete,

check the pre-heater on the air in take yesterday. You were right, turning the key counter-clockwise activates the pre-heater.

My pre-heater is working fine but was covered in oil from years of blow-by and generated a lot of smoke. I took it apart and cleaned the heating elements with an old toothbrush and that seemed to help.

[Britishsea]

Originally Posted by skipperpete

Here are what Yanmar call the “considerations” for your engine. Loss of power can be difficult to diagnose so a good mechanic will establish a base line by quickly and progressively eliminating all the easy stuff before addressing the less obvious causes so
Check the disconnected movement of the throttle lever under power
Check accuracy of tacho.
Check air filter
..........all fuel filters.
..........valve clearances
..........parasitic loads
......... exhaust for smoke.
..........exh back pressure

Then move on to the “crack injector line nut” to check individual cylinders.
Consider a completely separate fuel supply from a 20 litre can in the cockpit
Check return line for bubbles.
This proceeds towards more serious interventions such as cylinder leakage test, timing and injector pump check and maybe remove the cylinder head if any other tests indicate that as a reasonable next step. Attachment 244040

I was down on the boat yesterday checking to see if I could narrow this power loss issue to a particular cause.

I disconnected the fuel return line to the fuel tank and operated the lift pump by hand to check there was good flow through the primary and secondary filters and fuel lines. There was lots of flow through the system and no hint of any restriction.

I inspected all the fuel lines by hand for any soft spots, cracks or kinks. I replaced the fuel lines from the lift pump to the primary filter and from the primary filter to the high pressure fuel pump.

Skipperpete - I am not sure if the suggestion was to check the fuel return line for bubbles from the high-pressure fuel pump or the injectors ? But I put a temporary clear hose from the last fuel injector to the primary fuel filter to check for air bubbles. Two observations from this test that surprised me. First there was basically no excess fuel flow from the injectors' overflow return, regardless of RPM or load (at the dock) . Second, there were no bubbles when the engine was running, but bubbles appeared once the engine was stoped. Perhaps there was some negative pressure in the return line on engine shutdown and the connection was leaking air. See attached Pic.

I had previously checked the coolent temp sensor circuit by jumping its wire to the body of the sensor and it worked as expected and alarmed.

Wanting to double check I did not have a heat issue, I partially drained the heat exchanger of coolant and removed the sensor to check it in a pot of hot water on the stove with a volt meter (set to resistance). It was not working and never closed the connection even in boiling water.

So before I go any further, I am going to replace this temp switch sender and try to eliminate this as the cause.

I will continue to work on this a report back to the forum.

Thanks again for all your help everyone who has commented above.

BritSea

[Britishsea]

Sorry, my picture did not attach in my prior post.

[skipperpete]

Originally Posted by Britishsea

Sorry, my picture did not attach in my prior post.







Attachment 244101

Put the clear line on the third barb on the filter to tank return line, under some circumstances an injector can allow compression leakage back to the filter. That clear line on the return also gives a good indication of how well the lift pump valves are sealing, often the column of clear fuel out of the return just goes up and down, no bubbles but also no actual flow and it’s informative to know if the filter drains back to the tank after shutdown.... the valve on the suction side of the lift pump usually stops this if it’s sealing properly.
The hose clamp in your pic is likely the cause of the bubbles after shutdown as you pointed out.

[Compass790]

Disclaimer: I don't know your engine.
But we had no fuel going through the return line from injector on our little Yanmar before I replaced the delivery valve & plunger/barrel in the injection pump. The injection pump was not in good shape from water going through it
That should not be your problem on a 2000hr engine if it has always been fed clean dry fuel.
I'd certainly be going thru the easy stuff first before tackling the injection pump as Yammer mafia will ream you for that.
Also shouldnt be heat related problem AFAIK.
Just throwing it out there if you come to a dead end.
It actually doesnt cost too much to put an injection pump on a pump testing rig but wether the shop can be trusted not to do an unnecessary rebuild is another issue.
If your injectors are in good shape the injection pump should be too.