Problems with Yanmar L70 in MEP 016D

[Jim S]

I just got a low-hour MEP 016D with Yanmar engine. Would appreciate anyone with experience on the engine providing comments or suggestions. I've read everything I can find on this site and the web about the Yanmar L70

Background: It started easily after I changed all the fluids and flushed the fuel tanks/lines. But it runs very poorly. I can get it to rev up but when the governor engages it immediately slows to near stop with much missing and backfiring along the way. Then it speeds back up to near full speed with more missing and backfiring. I've tried every combination of throttle setting and no amount of fiddling seems to get the engine to smooth out at full throttle. The backfiring is so bad that I fear blowing out the muffler.

What I have tried: disassembled and cleaned the entire fuel system, including the injection lines, injection pump and fuel injector. All seemed in good order and the injector seems to fire cleanly from all four nozzles although I have no equipment to check the pressure. I timed the injection pump according to the TM. For good measure, I added and removed shims to both advance and retard the timing and the poor performance degraded further as expected. Valve clearance is good and compression seems fine although I have not checked with a gauge. The governor appears to be operating as intended and the various springs/levers attached to the external throttle assembly appear to be original and unmolested. Meter reads 1.59 hours and the Yanmar conversion appears complete with no evidence of maintenance or tampering, i.e. intact paint on all fasteners and adjustment points.

I am stymied in getting this to run properly. Any ideas on further things to check? I am fresh out of ideas short of tearing the engine down which I think is unlikely to yield good results since there is little reason to suspect internal problems.
JIm S

 

[SCSG-G4]

It almost sounds like one of the injectors is firing at the wrong time. If you can load it, bring it to the MVCSC meeting tomorrow night and we can have the crew look at it. Maybe someone's idea will work. Or wait till Tom or Jerry sees this thread and chimes in.

 

[derf]

There is a pin that goes into a notch when you install the injector. There is a little metal tab that you can remove to view the pin/notch relationship. Is the pin in the notch?

 

[derf]

Also, do you have TM 9-2815-257-24?

 

[Jim S]

derf,
Thank you for the comments. Yes, I have the TM and it has been very helpful, especially the injection pump timing procedure. And, yes, the injection pump pin is in the notch. I'm still stymied as to what might be wrong. The engine seems to be ingeniously designed. Very simple systems and well thought out. I don't want to break open the case since there is little inside that seems likely to produce the symptoms that I am getting. The only exception would be the governor assembly inside but it appears to be working as intended.
Jim

 

[derf]

The motor needs air and fuel, the right amount at the right time. Start with those. Make sure the IP isn't gummed up. The gens usually sit for months before auction and sometimes the fuel gets gummy in the pumps. Double check the valve clearances. Check intake path and exhaust path for obstructions. If all that seems good then check the gen head for binding and/or electrical problems. It should turn over easily with the compression lever down. There is a pretty big flywheel and a heavy gen rotor attached to the crank but with no compression it should spin easily.
After all that obvious stuff look hard at the governor. Maybe remove the little inspection plate and see if the IP lever pin stays still or moves as the engine runs.
Maybe check the valves, too. A sticky valve might cause trouble. It seems like there is a plug in the top of the valve cover for "2 cc" of lube or something like that.

 

[Jim S]

derf,
Thank you and I agree with everything you said.

I have checked and double checked everything you mention. Even before attempting to start, I thoroughly cleaned and purged the entire fuel system, from tank to injector. Nothing seemed amiss and before starting, I connected the injector to the fuel line and turned the engine over. The injector "popped off" as I would expect with a clean atomization from each of the four nozzles. The intake and exhaust paths are clean and unobstructed. I have run it both with and without the air cleaner - no noticeable difference. Valve clearances are correct. Generator shaft turns freely - no evidence of load on the engine during start-up or running.

Suspecting the governor, I have operated it with the IP inspection plate open. The IP throttle arm is activated by the governor as one would expect. The external governor linkage is intact and operates as one would expect. No looseness, binding or evidence of wear/abuse.

I agree with your initial statement regarding fuel, air, timing. All of those appear to be intact and in proper adjustment. The excessive backfiring makes me suspect excess fuel or gross timing maladjustment. Short of taking the engine apart to check the alignment of the cam timing marks, the valve timing seems correct. I can confirm the IP is timed correctly per the TM. Since IP operates on the same shaft as the intake/exhaust, I am further convinced the cam shaft is in correct alignment.

So the apparent excess unburned fuel has me puzzled. It makes me suspect one of two things: Either the IP is delivering too much fuel to the injectro or the injector is "popping" at too low a pressure and delivering excess fuel through the nozzles. I doubt the first condition since the throttle should compensate for excess fuel delivery, i.e. if the IP delivered too much fuel, the throttle would close to the point that fuel supplied would regulate the engine speed, just like the system is designed to work. As for the injector, I can only confirm that it is clean inside, nothing appears worn or plugged. I don't have any way to check the injector pop-off pressure or the amount of fuel being delivered. Even if I knew those figures, I don't know what the engine specs are for those.

I have pondered the condition of the piston and compression rings. It has plenty of compression to start so even if compression is on the low side, I doubt it is the problem. Besides, I cannot find what to expect for compression pressure. Have found the compression ratio in the TM from which I could possibly derive what to expect for cranking compression pressure.

My plan is to take off the external governor/throttle linkage and try to operate the engine without governor input. Essentially, manually overpower the governor to regulate the throttle by hand. If it runs properly in "manual" mode, I will strongly suspect something amiss with the internal governor linkage or some part of the external throttle control.

As for the lube port in the valve cover, I have not found any mention of it in the TM. The operating instructions placard on the unit says to add 2 ccs of engine oil before starting in low temp conditions. Presumably, that is to allow a bit of oil directly into the cylinder resulting in a slightly better compression seal to aid in starting.

Again, thanks for your interest and I welcome any critique of my thinking or understanding of this engine.
Jim

 

[Metalflames]

I just happened to read today that the is a procedure for fuel injection volume limitation not sure if you are aware of it. Go to page 99 (94 in the manual)

 

[ETN550]

It most likely needs the air bled out of the injection line, regardless of how good you think it is. The operation you describe is exactly like air in the fuel line. Some of these yanmars are VERY difficult to get a good bleed on. Here is a simple way to do it.

Fire it up. When it goes to high idle crack the injector line as it is running. As it falls down in speed snap the line shut before it stops and let it pick up speed. Repeat, repeat, repeat, etc until it runs out smooth and holds speed.

I'm 90% sure that is all you have to do.

Here is why it does what it does. The injecton system goes to full fuel when speed is below setpoint. Speed will pick up and fuel will come out in the exhust as air is in the system. At full speed the governor pulls back wanting to inject only enough fuel to keep it running which is such a small amount of fuel that it cannot push the air out so it drops off until speed is low and then it calls for max fuel again and the cycle keeps repeating.

By bleeding it as it runs down in speed the gov is calling for max fuel and it will purge the air with it. Then as it gains speed it is still at max fuel so the air continues to work out of it.

I have had to do this bleed procedure for about 3 - 5 minutes on an L10 recently.

IF this is not the problem then pull the valve cover and make sure one of the valves is not stuck.

 

[Jim S]

Thanks for the additional comments.

Metal - Greatly appreciate the Yanmar service manual. It answers several questions that I have had, such as the governor/throttle spring configuration and how to properly set the throttle. And it more clearly shows the injector and pump configuration. Unfortunately, the reference to fuel limiting adjustment appears to refer to what was done at the factory resulting in the index mark at the IP inspection window. But it does clarify how to use that mark to set the governor. I'll recheck mine over the weekend.

ETN - Thanks for the air bleed tip. Your explanation makes sense and I'll definitely try it. I've already checked for sticking valves and they seem free and operational.

I'll report back soon.
Jim