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Diesel troubleshooting
Excess fuel to the pumps goes to the return line. Unburnt fuel is fuel that
was injected and did not burn. Bad injector that does not atomize the fuel well, or injects too much fuel allows the fuel to not get burnt, and comes out the exhaust. Diesel semi's that are blowing black smoke are ejecting unburnt fuel. Bill "Dave R" wrote in message ... I don't think I can give you any advice but I just have a question. I've driven trucks all my life and by your post you say the problem might be unburnt fuel. That's what puzzles me. Every diesel I've driven always have a return line to the tank for unburnt fuel. Please forgive me if I completely ignorant on marine diesels but why would they not have a return line? I can tell you that the little amount of either that you used would not hurt anything. What kind of outside temps has your fuel been in? And how long has the diesel been in the tank? Have you switched fuel. Did you burn #1 or #2 diesel. Is it low sulfur diesel? I ask these questions because 4K hours to me is not a whole lot of hours. "Mike" wrote in message om... 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 |
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