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Message: [QUOTE="Peroni, post: 516128, member: 315"] Ok folks I got an odd one here. I built my electric fuel system 5yrs ago and aside from some bad luck with Walbro pumps it has been trouble free - until about 2 weeks ago. I heard a very loud buzzing while sitting at a stop light, got home and found it was the Bosch 69136 fuel pump I'm now using. I replaced it, new one sounded good for a few minutes then same thing. Changed filters - which were not that old - still got the noise. It gets worse when the fuel starts to heat up. This morning I hooked the pump up to an independent 12V source and watched it closely. For a few minutes it was fine then the buzzing started. Then I noticed tiny bubbles starting to appear in the clear bowl. They got more numerous the longer the pump was on but they stayed very small. I pulled the supply and return lines, stuck them in a bucket of fuel and turned the pump on, there were the little bubbles again. I tightened up the supply line going from the FM100 to pump, also checked the FM100's heater, sediment bowl and element locking ring all of which were tight. Somehow air must be leaking into the FM100? I have no external fuel leaks at all. I've got plenty of fuel flow thru the fuel manager to the pump so I don't think there is an internal restriction. Truck runs good but I've noticed that when I hear the buzzing I can drop fuel pressure to zero even in my stock tune when before the pressure would only drop off at wot on a hard dyno run. Sounds to me like a classic sign of cavitation. Has anyone ever had this problem with the FM100? I know it's a fairly popular filtration system for lots of diesels. Going to pull it tomorrow but not sure what if anything I might find wrong with it. [/QUOTE]