Yanmar 2QM20 running issues

[Wotname]

Curious mind wants to know...

You didn't try testing the existing injector pump in situ with one of the new injectors?

The logic pointing to faulty injection pumps sound good though. I hope the new injection pump fixes the problem.

The 200psi compression also sounds quite low to me but if it starts easy and runs well with the new head, injectors and injection pump, I guess it is good enough.

Looking forward to your next report!

[Cheechako]

How did you check the compression? You cant check 300 psi plus by hand holding the gauge in, you need a fitting and screw on gauge.

[skipperpete]

I was going to mention phase and calibration adjustments but if you’re getting a rebuilt pump it seems unnecessary because it will already be adjusted. Are you removing the delivery valve to do the timing?
Pete.

[Compass790]

The other thing I forgot to add is water could be getting in through a corroded exhaust manifold. Did you check that?

Edit: sorry see you said you checked it in OP

[charliehows]

it took me a while to get my 2qm20 running reliably because; the tank taps were leaking air; the fuel hoses were leaking air; the fuel filters were leaking air; I thought the mech. lift pump wasnt working so replaced it (still dont know if it was faulty so i keep the old one as a spare); the bleed screw on the injector pump was leaking air. Thing is, all those things were cheap to replace but collectively they created a hell of a mechanical conundrum. I've noticed mechanics tend to be "man with hammer only sees nails" ie. tend to focus on the mechanical (and expensive ) end of the motor...most diesel engine problems tend to be due to air leaks (tho' your discoveries under the head suggest other problems as well..) hope you have success getting the eng. running - they are excellent little motors once they are set up.

[Compass790]

Originally Posted by charliehows

it took me a while to get my 2qm20 running reliably because; the tank taps were leaking air; the fuel hoses were leaking air; the fuel filters were leaking air; I thought the mech. lift pump wasnt working so replaced it (still dont know if it was faulty so i keep the old one as a spare); the bleed screw on the injector pump was leaking air. Thing is, all those things were cheap to replace but collectively they created a hell of a mechanical conundrum. I've noticed mechanics tend to be "man with hammer only sees nails" ie. tend to focus on the mechanical (and expensive ) end of the motor...most diesel engine problems tend to be due to air leaks (tho' your discoveries under the head suggest other problems as well..) hope you have success getting the eng. running - they are excellent little motors once they are set up.

Too right re "man with hammer" but he has bad corrosion in 1 cylinder. Do you happen to know your 2QM20's compression reading in psi ?
Just OP's sounded way low to me.

[charliehows]

yes, i was a bit flippant but i did acknowledge his comments on the internals - I've never tested my compression, had the head off a few years ago and the picture was very pretty so it got a new gasket and nothing else - tho' i regret not adding some liquid reinforcing of the gasket around the pushrod galleys - its still weeping a bit of oil, which was why i had a look at it originally. Doh!
I guess the point i was trying to make was - older engine can develop complex problems but its always good to eliminate the fuel sys airleak first.

[kmacdonald]

Yep, multiple problems causing the same symptoms can be frustrating. You find and fix one problem and expect the engine to run but same problem. Multiple problems that cause weird symptoms are even harder. Don't let the little issues go and there is a lot less chance of that happening.

[Islandcruiser]

Well happy to report after being away for work, that my pump and fuel lines arrived. I have since installed both and timed the injection pump. Unfortunately the engine is still not running. It will start and run with 3/4 throttle for about 30 seconds. How ever it is white smoke when I do get smoke coming out. I still believe it is not firing on cylinder 2. Quite a vexing problem, I'm sure at this point I'm missing something somewhere. I do not believe it is fuel delivery now and have to say it is compression. How ever my tester does not have the correct tip to insert and I am not 100% sure of the test so I am looking for the proper tip to ensure my test is accurate.

I have called a shop to come have a look as I need a fresh set of eyes on it because at this rate I will lose another summer of sailing.

[Compass790]

Thanks for keeping us up to date,
Pity new pump didn't fix it but I'm not surprised.
You could get the shop to bring their compression tester, they are bound to have a dummy injector to fit a Yanmar.
One good thing is the 2QM20 is a wet sleeve engine if you have to rebuild.

[Wotname]

Hmm... I would be inclined to seperate the link between the two decompression levers and then try starting with one cylinder decompressed and see if the other cylinder fires OK. Then do it the other way around.

This might indicate if one cylinder or the other is compression challenged.

[kmacdonald]

The ignition pressure of diesel is 234 psi. 200 psi won't do it.

[kmacdonald]

Originally Posted by Compass790

Whilst I don't know what your compression is supposed to be, 200 psi sounds way low to me. The 2QM20 is 20:1 compression ratio. Our YSM8 is 23:1 & it's minimum compression reading is 355 psi. It's actual is 405 so I'd suspect your minimum would be around 300 psi.
Maybe someone who knows the 2QM20 can tell you

Yep, 294 psi. Thats with no carbon buildup. More with.

[Compass790]

Originally Posted by Islandcruiser

Well happy to report after being away for work, that my pump and fuel lines arrived. I have since installed both and timed the injection pump. Unfortunately the engine is still not running. It will start and run with 3/4 throttle for about 30 seconds. How ever it is white smoke when I do get smoke coming out. I still believe it is not firing on cylinder 2. Quite a vexing problem, I'm sure at this point I'm missing something somewhere. I do not believe it is fuel delivery now and have to say it is compression. How ever my tester does not have the correct tip to insert and I am not 100% sure of the test so I am looking for the proper tip to ensure my test is accurate.

I have called a shop to come have a look as I need a fresh set of eyes on it because at this rate I will lose another summer of sailing.

I forgot to say I dont think your method of working out the compression test psi reading works. I assume you just multiplied the compression ration by 14.5 ?
That method does not correspond to the figures Yanmar gives for a compression test on our engine. Yanmar figures are 397 to 454psi. std
& 355psi. minimum @ 200rpm but if you multiply the compression ratio of our engine ( 23:1 ) by 14.5 you only get 333.5

I don't know the way to calculate the psi reading on a compression tester from the compression ratio but maybe someone can help.

Sadly it's not looking good for your summer I suspect.

[kmacdonald]

Its 14.7 times compression ratio IIRC.