Yanmar 2QM15 won't start.

[sartorst]

One piece of advise that I give is that you should replace the filters after the engine is fully warmed up ! This will make the restart much easier many times the partial fuel injections only serve to wash the cylinder walls down lowering compression drawing battery's down which with too slow a cranking speed will not start and washes cylinders down further by that point if all is correct it may not start! Having said that using my own advise I replaced my filters on an engine with an electric lift pump which meant change filter open bleed bypass turn on key wait close bleeder start engine NOT !! Hours later I found a crack in the plastic plug on the suction side of the filter you could tell by the staining it had been that way for a long time but the problem shows up on the day I change filters go figure????

[uncle stinkybob]

Originally Posted by Tampabayfireman

What version of the racor do u have?

not sure of model # but it's a single, takes racor filter # R24S.

[uncle stinkybob]

Originally Posted by Cheechako

Did you fill up the racor to the top after installing the new filter? I always do that, but mostly because sometimes the engine would run for a few minutes and then die after new fuel filters. I'm not sure your pump will fill the Racor if the top is tight and the fuel has no where to go.... If you cracked at the right place that allowed your pump to fill up your racor.

No I didn't, but the 5 psi electric pump fills it and I use the bleed screw to bleed air off. Maybe somekind of air lock, broke when I changed the little filter today?

[uncle stinkybob]

Originally Posted by sartorst

One piece of advise that I give is that you should replace the filters after the engine is fully warmed up ! This will make the restart much easier many times the partial fuel injections only serve to wash the cylinder walls down lowering compression drawing battery's down which with too slow a cranking speed will not start and washes cylinders down further by that point if all is correct it may not start! Having said that using my own advise I replaced my filters on an engine with an electric lift pump which meant change filter open bleed bypass turn on key wait close bleeder start engine NOT !! Hours later I found a crack in the plastic plug on the suction side of the filter you could tell by the staining it had been that way for a long time but the problem shows up on the day I change filters go figure????

I do the same. This motor had been started maybe 3 hours earlier, not hot but not cold. Next time I'll warm it up right before I change them. Thanks for your advice!

[iancoombe]

Hi we have racour 500 pre system with a vacuum gauge, we changed a filer once and instantly the gauge shot up , we replaced it with another and it was fine never found the reason.

[19thol]

We had the exact same problem! After getting towed twice decided to change low pressure fuel pump, all good after that. Never had a pump that would work for four hours then give up, only to work next day like everything is fine, can really piss a person off!

[Don C L]

This is a great thread Uncle! I have only had to mess around with a Volvo MD7A but the more of these troubleshooting threads we have, the better I think. Maybe you could go in and rename the thread "Yanmar won't start" so that for those that have a similar problem in the future it will be easy to find in a search.

[uncle stinkybob]

Originally Posted by Don C L

This is a great thread Uncle! I have only had to mess around with a Volvo MD7A but the more of these troubleshooting threads we have, the better I think. Maybe you could go in and rename the thread "Yanmar won't start" so that for those that have a similar problem in the future it will be easy to find in a search.

Thats a good thought Don. I'll add that. I agree, stuff does not always go the way the manual says it should. Diagnostics can be a bear at times, more heads in the game the better. This thread did just that for me, well the guys that made me think outside of the normal "it must be" thinking, did that for me.
I'll get to the bottom of it cause it bugs the crap out me that I don't know, even if it is working now.
Maybe I'll fix it till it's broke again so I can get a proper diagnostic done.

[SteveInMD]

I'm not a mechanic by trade, but I have worked on a number of diesels. I'm curious, how do you bleed an injector on the return side? I thought it must be done on the high pressure side of the injector (the input to the injector). The return side should be very low pressure, if any, and should not require bleeding, right? If there is air on the supply side of the injectors they will never pop open and you will not make any progress bleeding the system. There must be no air between the high pressure pump and the injectors or the air will simply compress and the injector will not fire. I have only ever had a problem bleeding a motor when I try to skip steps and don't hit all the bleed points described in the manual for that particular motor, in order.

[uncle stinkybob]

Seems I can't change the title to
Yanmar 2QM15 won't start.
Is there a chance one of our nice mods can change the title for me?

[uncle stinkybob]

Originally Posted by SteveInMD

I'm not a mechanic by trade, but I have worked on a number of diesels. I'm curios, how do you bleed an injector on the return side? I thought it must be done on the high pressure side of the injector (the input to the injector). The return side should be very low pressure, if any, and should not require bleeding, right? If there is air on the supply side of the injectors they will never pop open and you will not make any progress bleeding the system. There must be no air between the high pressure pump and the injectors or the air will simply compress and the injector will not fire. I have only ever had a problem bleeding a motor when I try to skip steps and don't hit all the bleed points described in the manual for that particular motor, in order.

there is always positive fuel pressure because of the lift pump, it's the high pressure injector pump, cam drive, cam timed that provides the increase in pressure that opens the injector valve body to spray fuel in combustion chamber. bleeding at the return side should be the fuel being delivered at 5 psi by my lift pump. the return side of the injector pump scavenges the fuel for return from there. I'm not sure I explained that very well.

[jimbunyard]

Originally Posted by uncle stinkybob

OK, engine is RUNNING! why? I don't have a damn clue. I started looking at injector pump, cracked fuel feed line, no presssure? wtf? I have pressure at injectors, yes, but I always bleed injectors on return side, works fine. But when I actually cracked the fuel feed line at injectors, no pressure, WTF? feed line=no, return line=yes. I went back to engine mounted fuel filter, cracked feed side line=no, cracked return line=yes. The only thing I changed was the filter here so I swapped out another new one, different brand (wix) bleed system, motor fired up like it was no big deal. WTF? A filter is a simple little thing, can't find anything different between the two and I dont think there is. A gremlin? he jumpin the first filter change and jumped out on the second?
I've been a mechanic a long time, Master of Technology cert with H.D., it's not the first time strange unexplained crap like this has happened to me but it rubs me badly. As a mechanic I have to know why? What? will it repeat? What failed? and I find nothing here. She runs as well as she ever did so.....off we go! Thanks for all the help here, as always, when I get advice from you folks, it keeps my wheels turning and I decided to go beyond what I "know" it can't be to "it could be anything or everything.
Thanks everybody! I love this site.

Originally Posted by SteveInMD

I'm not a mechanic by trade, but I have worked on a number of diesels. I'm curious, how do you bleed an injector on the return side? I thought it must be done on the high pressure side of the injector (the input to the injector). The return side should be very low pressure, if any, and should not require bleeding, right? If there is air on the supply side of the injectors they will never pop open and you will not make any progress bleeding the system. There must be no air between the high pressure pump and the injectors or the air will simply compress and the injector will not fire. I have only ever had a problem bleeding a motor when I try to skip steps and don't hit all the bleed points described in the manual for that particular motor, in order.

Originally Posted by uncle stinkybob

there is always positive fuel pressure because of the lift pump, it's the high pressure injector pump, cam drive, cam timed that provides the increase in pressure that opens the injector valve body to spray fuel in combustion chamber. bleeding at the return side should be the fuel being delivered at 5 psi by my lift pump. the return side of the injector pump scavenges the fuel for return from there. I'm not sure I explained that very well.

While the original new filter could surely be defective, almost certainly the cause of the problem was air in the injection pump. As noted by Steve above, it is much easier to compress air than diesel fuel, and that appears to be what was happening.

The injection pump provides pressure to what we all call injectors but are actually correctly called nozzles, somewhere north of 3-4000 psi. This pressure is produced by a device within the pump called a plunger and bushing, which is exactly what it sounds like, but machined and polished to very close tolerances, hence the need for effective filtration and the pumps' dislike for dirt.

The high pressure side of the pump has to be full of fuel, no air, to operate correctly. Likewise for the high pressure line from the pump to the nozzle.

I don't know your procedure, but if you install the filters dry, turn on the feed pump and let that fill your filters, then you are pushing the amount of air that the filters contain through the system, hoping that all the air will purged. In such a highly convoluted system, I'd say 'hopelessly hoping'.

If you use a pump, electric or hand, to fill your filters, it's probably best to leave the filters loose, pump the fuel until it starts to spill out, and then tighten them fully, thus avoiding introducing unnecessary air into the system.

Somewhat counterintuitively, in this instance fewer cylinders can make things harder. Roughly speaking, on a single cylinder engine, the injection must be perfect, on a 2 cylinder, you have a 50% chance of getting things right, on a 3, 33%, and so on; the good cylinder(s) will support the bad (unbled) cylinder until the air gets worked out. Which is why starting fluid (or whatever your weapon of choice is) can often be used to get reluctant engines going. (A side note, not to get anyone excited, but starting fluid, ether, is nothing but a tool. Like all tools, used correctly they make life easier, used incorrectly, they can have catastrophic results...)

A couple of years ago I had a little horizontal Kubota single cylinder that had to be bled by loosening the fuel inlet on the injection pump, apparently because this was the highest free space in the high pressure side of the injection system. I could bleed it all day long at the high pressure nut on the injector (nozzle), fuel would shoot out but the engine would not start unless bled at that one point.

Most engines have certain idiosyncrasies...

[bony]

Hi Uncle Stinkybob,

I don't know if your 2qm15 behaves like mine does but whenever I need to bleed my fuel system I simply cannot get it to start without first cracking the two nuts at the front from which the injector lines issue from (See photo below). I know you should only have to crack the bleed screw and the feed line nuts on the injectors, and I always do this, but my engine still stubbornly refuses to fire until I bleed the air from the lines by loosening nuts pictured. I had to modify a spanner to make it fit the inner nut but once they are bled she starts no problem.

Hope this helps,




bony.

[SteveInMD]

Originally Posted by bony

Hi Uncle Stinkybob,

I don't know if your 2qm15 behaves like mine does but whenever I need to bleed my fuel system I simply cannot get it to start without first cracking the two nuts at the front from which the injector lines issue from (See photo below). I know you should only have to crack the bleed screw and the feed line nuts on the injectors, and I always do this, but my engine still stubbornly refuses to fire until I bleed the air from the lines by loosening nuts pictured. I had to modify a spanner to make it fit the inner nut but once they are bled she starts no problem.

Hope this helps,



bony.

If that works for you - good. If some day that method doesn't work, I believe the official procedure for bleeding the high pressure side is to not crack open the nuts you mention, but follow the two lines to the injectors and crack both those nuts open by a full turn. Crank the motor until you get clear fuel at the injectors, tighten the nuts, and then start the motor.

[HappyMdRSailor]

Originally Posted by SteveInMD

I'm not a mechanic by trade, but I have worked on a number of diesels. I'm curious, how do you bleed an injector on the return side? I thought it must be done on the high pressure side of the injector (the input to the injector). The return side should be very low pressure, if any, and should not require bleeding, right? If there is air on the supply side of the injectors they will never pop open and you will not make any progress bleeding the system. There must be no air between the high pressure pump and the injectors or the air will simply compress and the injector will not fire. I have only ever had a problem bleeding a motor when I try to skip steps and don't hit all the bleed points described in the manual for that particular motor, in order.

I caught this too... If you've got a no start from a quickee bleed, injector feed lines are your 1st "go to"...

Originally Posted by uncle stinkybob

there is always positive fuel pressure because of the lift pump, it's the high pressure injector pump, cam drive, cam timed that provides the increase in pressure that opens the injector valve body to spray fuel in combustion chamber. bleeding at the return side should be the fuel being delivered at 5 psi by my lift pump. the return side of the injector pump scavenges the fuel for return from there. I'm not sure I explained that very well.

I think you explained it fine... BUT... There's relief spring pressure in the injector for the return that won't be overcome (usually) by a feed pump... Meaning... You gots to haves yer main pressure line full of fuel so the IP can "bleed" the return...

Originally Posted by uncle stinkybob

Seems I can't change the title to
Yanmar 2QM15 won't start.
Is there a chance one of our nice mods can change the title for me?

Did you get the title changed to what you wanted?