Home |
Search |
Today's Posts |
#11
|
|||
|
|||
Diesel troubleshooting
The Cummins system senses manifold pressure so although your turbos need service (maybe) the lower pressure shouldn't mean excess fuel getting injected. Certainly get the unit injectors serviced, it's more likely poor fuel injection pressure or atomisation causing the unburnt fuel out the exhaust. Once the injectors are up to snuff, the new performance will probably bring the turbo pressure up a bit also. The turbo(s) have full floating plain bearings with lots of clearance/play in all directions so despite being more than "spec" if they're not allowing oil "in" they are not likely to be the root cause of your problem. K Mike wrote: I have 2 Cummins 6bt5.7M (4k hours) that are beginning to smoke and leave a film at the exhaust (sea water output). The port engine is the worst, but both engines have the same problem. In trying to identify the problem I've preformed the following test. 1) no (or very little) oil usage. 2) Both Engines run at 180 deg. 3) Turbo output 2600rpm (port)16psi (starb) 18psi Cummins manual calls for 20-25psi. No intake obstructions. No leaks detected any place from output of turbo up to and including the intake manifold. No detectable leaks in exhaust. No restrictions in oil return line. 4) Turbo (Holset H1C) compressor impeller can be pushed to contact the housing. (I would guess .100" movement) Holset calls for .012" - .018" radial movement 5) Turbo axial movement .010 both sides. Holset calls for .025. 6) Blowby (taken with the Cummins recommend setup using calibrated 0-100"h20 gauge with dipstick hole blocked). at 1000rpm approx. 2" (both engines) but at 2600 rpm 0". (I've ordered a diesel compression tester hope to have it next weekend while I'm testing the compression, I'll get the injectors tested) These are the steps that I've taken so far. The most glaring result to me is the blowby. There is none detected at rated speed. I've talked to the Cummins dealer, he says that it can't be and recommend using a manometer instead of the gauge. The turbo's are bad according to the holset manual so I pulled them and brought them to be rebuilt (holset authorized). The mechanic looked at them when I dropped them off and While he didn't come out and say so, I got the impression that he thought they were ok. He will be taking them apart this week. OK, now for my diagnosis; The smoke and sheen that I see are unburned diesel. The cause is low turbo pressure not getting enough air into the cylinders. The low turbo pressure is Caused by bad oil seals in the turbos allowing crankcase pressure to be reduced by the vacuum of the turbo compressor. The question of why would both engines have the same problem comes up. My theory is; when changing fuel filters, I use starting fluid to get the fuel to start. The ether (or other chemicals in the starting fluid) has caused the seal to deteriorate. Anyone have any feedback? The engines are honey's. They have never failed in the 10 years we've owned the boat ( 3000hrs). The smoke is not a killer yet, but I would like to solve the problem before it gets worse. Thanking anyone in advance for advice, criticism or observations. Mike |
#12
|
|||
|
|||
Diesel troubleshooting
Mike wrote:
1) no (or very little) oil usage. Check for fuel dilution. 3) Turbo output 2600rpm (port)16psi (starb) 18psi Cummins manual calls for 20-25psi. Worn turbos are less efficient. Worn bearings will limit turbine speed and reduce output pressure. How much power or boat performance have you lost? Turbo output pressure is related to the load on the engine, and atmospheric pressure and temperature, not just rpm. There are a number of reasons why the pressure might be low ... what was it before you decided you had problems? Do you know what it was? The smoke and sheen that I see are unburned diesel. Are you positive it is fuel? Do the engines smoke black on acceleration and under heavy loads? What color is the smoke at low speeds? How much power have you lost? turbo pressure not getting enough air into the cylinders. The low turbo pressure is Caused by bad oil seals in the turbos allowing crankcase pressure to be reduced by the vacuum of the turbo compressor. ????? Crankcase pressure related to turbo vacuum? Sorry but you have a diesel, there is no "vacuum" created anywhere. There is a low pressure area in front of the compressor wheel but unless your air inlet is blocked there is no vacuum like you might see in a gasoline engine. The only effect you would see if you have bad oil seals in the turbo would be oil leaking into the charge air and being delivered to the cylinders or blue oil smoke in the exhaust. Check the condition of the intake piping to see if it is wet with oil, check the condition of the exhaust from the turbo after a period of idling to see if it is wet with oil. It sounds like that is irrelevant now that you have removed the turbos for rebuild but file that away for the future. Worn injectors will cause poor combustion and can create most of the symptoms you describe. As long as you have no starting problems you have no compression problems. You may have cylinder wear and worn injectors which lead to fuel dilution of the lube oil. This is cause for concern. Check with Cummimns for their recommendation on maximum allowable dilution limits. Good luck and get back to us with the results of your investigations. |
#13
|
|||
|
|||
Diesel troubleshooting
|
#14
|
|||
|
|||
Diesel troubleshooting
Short Wave Sportfishing wrote:
Is your generator a Kubota three cylinder? I had this exact same problem last year with the one here at the house and it was crap in the fuel tank and line - sludge actually. I think it's a Yanmar, it's a Onan 4.5kW genset. It's a job for this coming weekend, check the fuel flow. The filters are clear but it's possible that the suction line connection to the tank is blocked. Fair Skies Doug King |
#15
|
|||
|
|||
Diesel troubleshooting
Subject: Diesel troubleshooting
From: (Florida Keyz) If you really wish to get inteligent answers, you may want to try rec.boats.cruising. It's a moderated group with boaters. No O.T. posts. Is this OT post going to be your standard response to all questions on rec.boats now? And by the way, rec.boats.cruising it NOT moderated. Capt. Bill |
#16
|
|||
|
|||
Diesel troubleshooting
Florida Keyz,
I think you're wrong about this. The group is not moderated. True though about the number of OT posts. Paul "Florida Keyz" wrote in message ... If you really wish to get inteligent answers, you may want to try rec.boats.cruising. It's a moderated group with boaters. No O.T. posts. |
#17
|
|||
|
|||
Diesel troubleshooting
"Rod McInnis" wrote in message ...
"Mike" wrote in message I have 2 Cummins 6bt5.7M (4k hours) that are beginning to smoke and leave a film at the exhaust (sea water output). - Is this at all speeds, or only under wide open throttle? (okay, diesels -aren't throttled, but I never picked up what the proper term for a diesel -is....). If it is WOT only, is this slick so obvious you can see it going -full speed? -Other than the oil in the water, how are the engines running? Still giving -you the same performace as before? How about fuel usage? They are both smoking at all speeds, port more than starbord. Other than the smoke (again, not exceesive but more that I would like) 3) Turbo output 2600rpm (port)16psi (starb) 18psi Cummins manual calls for 20-25psi. - Is this measurement taken while under load, or while in neutral? I -wouldn't expect the turbos to be working very hard unless the engines were -heavily loaded. Engine RPM does not indicate turbo RPM. This is taken full throttle (I don't know what else to call it either) under load (about 16knts). OK, now for my diagnosis; The smoke and sheen that I see are unburned diesel. - Probably. The cause is low turbo pressure not getting enough air into the cylinders. -Only if this problem is occuring at or near WOT conditions. If this problem -happens at idle speeds (which is when I would expect you would be able to -see the sheen in your wake) then it isn't the turbo. there seems to be more smoke at idle speeds. That may be because the there is air movement. I talked to the turbo rebuild tech today, he found one bad turbo, (exhaust blade hitting the housing) the port side. He said the starboard was in fair condition. The low turbo pressure is Caused by bad oil seals in the turbos allowing crankcase pressure to be reduced by the vacuum of the turbo compressor. -I don't follow you here. -If there aren't any obstructions in the turbo intake (like an air filter) -then there shouldn't be much vacuum generated. I am not familiar with this -engine at all, so I don't understand how the crankcase pressure and turbo -are related (the turbos I am familiar with have been mounted external to the -engine and don't have any connection to the crankcase that could leak). -If the problem were bad oil seals, however, then I would expect that there -would be a loss of oil. If the leak went external then it should be making -a mess in the engine room. If the leak went internal then I would expect it -to just be burned, only showing up in the fact that you have to add oil -often. Yeah, I don't blame you for being confused, I worked out this elaborate scenerio to explain the lack of blowby. Anyone have any feedback? The engines are honey's. They have never failed in the 10 years we've owned the boat ( 3000hrs). The smoke is not a killer yet, but I would like to solve the problem before it gets worse. -When was the last time you had the injectors serviced? -A diesel engine requires a little bit more than just squirting the fuel into -the cylinder. Part of the injectors job is to atomize the fuel as it is -injected so that it can burn. Vaporized fuel will ignite and burn. Liquid -fuel will NOT burn. -A worn injector can allow a portion of the fuel to enter as a liquid stream. -Some of this will boil and burn, but portions of it will remain liquid, not -burn and then go out the exhaust, causing your problem. -The last time I had injectors serviced it cost me $125 an injector. I took -them off, brought them down to a shop that specializes in diesel fuel -systems. They had them about a day and then I picked them up and put them -back on. An engine I was about ready to throw the towel in on ran great -after that. -If your injectors have 3000 hours on them, then I wouldn't hesitate to have -them serviced. Whoa! 125/injector... I agree, I will be removing them as soon as I get the turbos back on. (hopefully this weekend). Thanks a lot for the response Rod. |
#18
|
|||
|
|||
Diesel troubleshooting
"K. Smith" wrote in message ...
The Cummins system senses manifold pressure so although your turbos need service (maybe) the lower pressure shouldn't mean excess fuel getting injected. Certainly get the unit injectors serviced, it's more likely poor fuel injection pressure or atomisation causing the unburnt fuel out the exhaust. Once the injectors are up to snuff, the new performance will probably bring the turbo pressure up a bit also. The turbo(s) have full floating plain bearings with lots of clearance/play in all directions so despite being more than "spec" if they're not allowing oil "in" they are not likely to be the root cause of your problem. K thanks for the reply K. On of the turbo's did have serious a problem, but the other didn't. The injectors are next on the list. |
#19
|
|||
|
|||
Diesel troubleshooting
Rick wrote in message ink.net...
Mike wrote: 1) no (or very little) oil usage. Check for fuel dilution. Thanks for the suggestion.I will add oil testing to the list. 3) Turbo output 2600rpm (port)16psi (starb) 18psi Cummins manual calls for 20-25psi. Worn turbos are less efficient. Worn bearings will limit turbine speed and reduce output pressure. How much power or boat performance have you lost? Turbo output pressure is related to the load on the engine, and atmospheric pressure and temperature, not just rpm. There are a number of reasons why the pressure might be low ... what was it before you decided you had problems? Do you know what it was? I first noticed the sheen this past November. The smoke has been increasing over the last year or so. As for power, I can't say that I've notice any change. Most of my cruising is done around 1800 rpm (8-9knts) The smoke and sheen that I see are unburned diesel. Are you positive it is fuel? Do the engines smoke black on acceleration and under heavy loads? What color is the smoke at low speeds? How much power have you lost? If I throttle up rapidly while underway, the smoke is black until the boat gets up on a plane, then to white (slight blue mabey). In all other conditions the smoke is whitish (slight blue mabey) turbo pressure not getting enough air into the cylinders. The low turbo pressure is Caused by bad oil seals in the turbos allowing crankcase pressure to be reduced by the vacuum of the turbo compressor. ????? Crankcase pressure related to turbo vacuum? Sorry but you have a diesel, there is no "vacuum" created anywhere. There is a low pressure area in front of the compressor wheel but unless your air inlet is blocked there is no vacuum like you might see in a gasoline engine. with the air filters on there is a slight vacuum that increases as the air filter gets dirty. The only effect you would see if you have bad oil seals in the turbo would be oil leaking into the charge air and being delivered to the cylinders or blue oil smoke in the exhaust. Check the condition of the intake piping to see if it is wet with oil, check the condition of the exhaust from the turbo after a period of idling to see if it is wet with oil. It sounds like that is irrelevant now that you have removed the turbos for rebuild but file that away for the future. Worn injectors will cause poor combustion and can create most of the symptoms you describe. As long as you have no starting problems you have no compression problems. You may have cylinder wear and worn injectors which lead to fuel dilution of the lube oil. This is cause for concern. Check with Cummimns for their recommendation on maximum allowable dilution limits. Good luck and get back to us with the results of your investigations. The next step will be to get the injectors looked at. Then the oil test. While I'm removing the injectors I will also get the compression. UPS just delivered my diesel compression tester. Thanks for the reply. Mike |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Diesel Quality Varies....(?) | General | |||
Diesel Fuel Decontamination Units Give Stored Fuel Longer Life. | General | |||
Diesel Engine Sounds | General | |||
Why Ficht failed no1 | General | |||
Emergency diesel shutdown | General |