Mep531a.wont start or hit

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Shadetreeguy

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Just purchased a mep531a and started messing with it try to get it running but for some odd reason it's filling crankcase full of fuel.I first thought it had a bad fuel pump so I changed it and bled the lines and truer again then I found the oil level was laying in my floor when I opened the dipstick.could it be home in piston or bad rings or am I over thinking the situation.I'm a pretty decent mechanic and started diesel mechanics bout 5 year ago and I understand that if it has air fuel combustion it should run.and also had injector out while cranking and it was spraying and when I shine light in cylinder it looks full of fuel...please help.I'm debating whether or not to do a overhaul on the motor.its only got 100 hours.
 

Shadetreeguy

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I changed the fuel pump.its getting fuel to the injector.and had the injector out while cranking it and it was spitting fuel good out of the injector.but I noticed that the crankcase was full of diesel fuel.would the oil sensor keep it from running.it seemed like to me that if it was getting fuel and air and compression it should run no matter what????? It sounds like it has compression.
 

Guyfang

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I changed the fuel pump.its getting fuel to the injector.and had the injector out while cranking it and it was spitting fuel good out of the injector.but I noticed that the crankcase was full of diesel fuel.would the oil sensor keep it from running. (no it would not. ) it seemed like to me that if it was getting fuel and air and compression it should run no matter what????? It sounds like it has compression (don't guess, test).


Think now about where the fuel and oil systems meet.
1. The IP. could the IP be letting fuel bleed by, and drain into the oil system? The IP is driven by the crank/engine. So its possible. But it needs to be checked. I have never seen or heard of this type problem.
2. The injector/cylinder. Could the injector, be "stuck open", by that, I mean not opening, closing? Just open? If the cylinder has compression, (remember, CHECK, don't guess) then there is no other way for fuel and oil to mix. The set has no mechanical fuel pump, (the most likely place to mix, on small engines) so where else could it be?
 

Scoobyshep

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Fuel timing is important. We had a few busses at work loose the injection pump seal and they flooded the crank case with fuel, so it does happen from time to time.

Sent from my SM-G950U using Tapatalk
 

Shadetreeguy

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Ok.I'm trying to find away to test compression now.I've got a compression tester but its to big.but ill rig something to fit.what are you guys calling the IP..is it what I'm calling the fuel pump.I ordered a new one and same thing.its spitting bubble from bottom of it when I'm cranking it over.where my finger is pointing.and I pulled injector and it was pulsing as I was cranking.
 

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Shadetreeguy

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Ok.I'm trying to find away to test compression now.I've got a compression tester but its to big.but ill rig something to fit.what are you guys calling the IP..is it what I'm calling the fuel pump.I ordered a new one and same thing.its spitting bubble from bottom of it when I'm cranking it over.where my finger is pointing.and I pulled injector and it was pulsing as I was cranking.
OK.check compression.120 pounds should be Plentys to run.?????would the injector cause this.if so ill order one now
 

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Dieselmeister

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When you say filling the crankcase with fuel" , how much fuel are you getting in there? There are only two ways for fuel into the crankcase; through the pump, or past the piston/rings. The pump only pumps about a drop per injection cycle. You would have to crank the engine for quite a while to get a noticeable amount of fuel into the crankcase. I would remove the pump, but leave the fuel supply hose connected, then see if any fuel drips out the bottom of the pump. Could be someone previously messed with the pump/pump piston.

Did your injector have the plastic bushing, and spacer ring/gasket? I didn't see that in the picture.

For the low compression, squirt some oil into the cylinder, and see if that changes the compression. Also check the valve clearance. Could be a open valve, or stuck rings, or worse. Start by testing the simple stuff, and work up from there.
 

Shadetreeguy

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When you say filling the crankcase with fuel" , how much fuel are you getting in there? There are only two ways for fuel into the crankcase; through the pump, or past the piston/rings. The pump only pumps about a drop per injection cycle. You would have to crank the engine for quite a while to get a noticeable amount of fuel into the crankcase. I would remove the pump, but leave the fuel supply hose connected, then see if any fuel drips out the bottom of the pump. Could be someone previously messed with the pump/pump piston.

Did your injector have the plastic bushing, and spacer ring/gasket? I didn't see that in the picture.

For the low compression, squirt some oil into the cylinder, and see if that changes the compression. Also check the valve clearance. Could be a open valve, or stuck rings, or worse. Start by testing the simple stuff, and work up from there.
OK.ill start eliminating stuff.so 120psi is to low?. I didn't see any bushings or seals or orings on the injector.and I haven't put any new oil in it yet to find out how much fuel is getting in the crankcase but when I pulled the dipstick when I got it it was pouring out.on level surface.and when I crank it it blows oil out of dipstick hole pretty good without the dipstick in it.I just don't want to sink a bunch of mo ey in it and not be able to get my money back outta it.its a nice clean machine.thought it was something simple so I traded for it
 

Shadetreeguy

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Wayne wv
When you say filling the crankcase with fuel" , how much fuel are you getting in there? There are only two ways for fuel into the crankcase; through the pump, or past the piston/rings. The pump only pumps about a drop per injection cycle. You would have to crank the engine for quite a while to get a noticeable amount of fuel into the crankcase. I would remove the pump, but leave the fuel supply hose connected, then see if any fuel drips out the bottom of the pump. Could be someone previously messed with the pump/pump piston.

Did your injector have the plastic bushing, and spacer ring/gasket? I didn't see that in the picture.

For the low compression, squirt some oil into the cylinder, and see if that changes the compression. Also check the valve clearance. Could be a open valve, or stuck rings, or worse. Start by testing the simple stuff, and work up from there.
Ppoured oil in cylinder it jumped to 280 and hit so now what
 

Dieselmeister

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Since you got it with so much oil that it was pouring out, I suspect the previous owner overfilled the crankcase with oil. Drain some of it out, to the middle of the markings on the dipstick (with the dipstick screwed in). The Yanmar 48's are very sensitive to too much oil, and will run like crap if overfilled. If in doubt about the oil quality, change the oil.

If it is truly diesel in the crankcase, it could be the previous owner was trying to clean out the crankcase or something else.

Since you got 280 psi with oil in the cylinder, I suspect either a ring problem (95%) or a leaky valve (5%). Worst case could be a broken ring or piston problem, but that should not be with only 100 hours.

Take off the valve cover, and check the valve clearances with a feeler gauge, per the manual. If the clearances are good, then it's probably a stuck ring problem. You could either fill the cylinder with something like Marvel Mystery oil, and let it soak for a day or two, then suck out the MM oil, and try the compression test or running it again. (Any idea how long this engine had been sitting without being run or cranked)?

The brute force way would be to squirt some oil in there, and if it starts, let it run for a little, then check the compression again.

Remember - Never assume that the previous owner knew what they were doing with this engine. Of the 4 Yanmar's I bought so far, only one of them had a problem, and that was because someone in the previous organization did not follow procedure, and attempted to repair a non existent problem. It usually takes "human input" to destroy one of those little Yanmars. Otherwise they will outlast us.
 

Shadetreeguy

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Wayne wv
Since you got it with so much oil that it was pouring out, I suspect the previous owner overfilled the crankcase with oil. Drain some of it out, to the middle of the markings on the dipstick (with the dipstick screwed in). The Yanmar 48's are very sensitive to too much oil, and will run like crap if overfilled. If in doubt about the oil quality, change the oil.

If it is truly diesel in the crankcase, it could be the previous owner was trying to clean out the crankcase or something else.

Since you got 280 psi with oil in the cylinder, I suspect either a ring problem (95%) or a leaky valve (5%). Worst case could be a broken ring or piston problem, but that should not be with only 100 hours.

Take off the valve cover, and check the valve clearances with a feeler gauge, per the manual. If the clearances are good, then it's probably a stuck ring problem. You could either fill the cylinder with something like Marvel Mystery oil, and let it soak for a day or two, then suck out the MM oil, and try the compression test or running it again. (Any idea how long this engine had been sitting without being run or cranked)?

The brute force way would be to squirt some oil in there, and if it starts, let it run for a little, then check the compression again.

Remember - Never assume that the previous owner knew what they were doing with this engine. Of the 4 Yanmar's I bought so far, only one of them had a problem, and that was because someone in the previous organization did not follow procedure, and attempted to repair a non existent problem. It usually takes "human input" to destroy one of those little Yanmars. Otherwise they will outlast us.
Well I drained the oil and tried starting it again and nothing again.and without oil on top of cylinder it only has 120 psi.I'm guessing that rings may be stuck or bad rings or possibly bad valves.I'm gonna try the marvel oil today.is there anyway that the seals that seal the injector is bad.injector seems to fall in the hole to easy and pulls out to easy.I've changed a lot of injectors in Ford's and duramaxs and they usually have to be pulled in and out.where do I order parts from or does anyone buy these gens for parts if I can't get it going
 

Shadetreeguy

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Wayne wv
And it wasn't all oil when I drained it.it was half oil half fuel.the guy I got it from acted like it ran perfect but believe he was just saying that so I'd buy it
 

Dieselmeister

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Flagstaff, Az
is there anyway that the seals that seal the injector is bad.injector seems to fall in the hole to easy and pulls out to easy.

The injector has a plastic gasket and metal spacer that seal it in place. It should not "fall" in the hole. When you look into the injector hole you should see the plastic gasket. The metal spacer is usually on top of it, unless it's stuck to the injector. See page 0019-2 in the manual. This plastic gasket usually needs to be replaced if removed, since there is no easy way to remove it (usually threading a bolt into it, and pulling it out). Hopefully that metal spacer is not bouncing around in the air intake housing. All these parts are available from Yanmar vendors, vendors on this site, and e-pay.

Looks like your main problem will be tracking down the reason for the low compression. The compression ration for this engine is 19.9:1 which is about 300#.

Have you downloaded the manual? TM 9-6115-673-13&P
 

RobertoGatos

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How are you checking compression? If your utilizing the decompression lever while pull starting the engine, the indicated compression could be lower than your actual to allow the pull start. Maybe try connecting a slave cable and e-start before you tear down the motor... just to be certain.
 

Shadetreeguy

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How are you checking compression? If your utilizing the decompression lever while pull starting the engine, the indicated compression could be lower than your actual to allow the pull start. Maybe try connecting a slave cable and e-start before you tear down the motor... just to be certain.
I'm using a compression tester and a battery with electric start.I really believe that injector seal has something to do with my problem
 

Shadetreeguy

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I've downloaded a couple different manuals but don't believe they are right and I honestly believe the seal is my problem bc like I said the injector almost falls I to place
 

Guyfang

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I'm using a compression tester and a battery with electric start.I really believe that injector seal has something to do with my problem
If the seal is bad, you should see/hear it. If you think its a problem, put a little water around the injector, and spin it over. If you have a loss of compression, you will know it.
 
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