Buzzzzzzzzzzzzzzzzzzzzzzzzzzz

Alex Bruene · October 1, 2019

Hello gentlemen (and ladies? I haven't been here in a while, so I'm not sure what's changed)…

Here's my head scratcher.

I replaced a fuel injector on a 6.7 the other day for a misfire. I also had to remove all the injectors on the right bank to have some broken hold down bolts extracted. Ever since, there is a loud buzzing coming from the secondary filter - running, or KOEO. The noise was not there before doing the repair. I replaced the filters to see if they were the cause of the buzz, but it didn't change anything. If I key on and off several times, the buzz stops. Once I start the engine, it returns. It will continue until I key on and of several times again. Can I be sucking air somewhere while the engine is running causing this - in a way that wouldn't lead to an external leak? Thanks!

Bruce Amacker · October 2, 2019

Commonly a suction leak at the primary FF or a crack on the fuel sending unit at the suction line. As for the coincidence, stranger things have been known to happen.....

Good Luck!

Alex Bruene · October 2, 2019

I'm going to add some fuel to it later today to see if it changes. I was thinking the same in regards to the sending unit. Thanks.

Bruce Amacker · October 2, 2019

I don't see how adding fuel will help. There's likely a suction leak somewhere, the primary FF is the first place I'd check, like a rolled o-ring. (What year? I'm assuming it's not a late 6.7) The next likely place is a crack in the sender where the arrow is pointed (not sure which hose), supposedly on some chassis the suction line is kind of tight and produces a crack in the bottom of the nipple on top of the sender. If nothing proves out with the primary FF I'd be inclined to put a stethoscope near this area and listen. You might hear a whistle or hiss.

A while back I did a 6.7 class, told them about the buzz problem, and went into the shop to do the hands-on portion of the class. We could hear the buzz from 100 feet away as they pulled the truck into the bay! They had changed the filters recently and the secondary filter twice trying to cure the buzz.

Good Luck!

cbriggs · October 3, 2019

I have seen the cracked nipple on top of the sending unit multiple times. About half of those were not evident until after touching an unrelated part of the fuel system, usually fuel filter replacement.