6.9 woofing

[gunnie]

Hi guys, i have a chance to pick up a 6.9 really cheap, but it has a woofing sound coming from the intake. what are the possibilities?
thks gunnie

 

[Dieselguy123]

I have friend who has a 91 7.3 that was making a woofing type sound also....He took it in and said that it had somthing to do with the valvetrain. Not really sure what, he has been driving it like that for about a year now and hasnt had any problems, just thought I would let you know that.

 

[Mr_Roboto]

Usually a valve problem. Mine starts tapping and woofing if I'm low on oil and run on the highway. I'm guessing one of the lifters sticks. I top off the oil and let it run a couple minutes and it's OK again.

Basically the "woofing" sound is a valve hanging open and the compression coming right back out.

 

[gunnie]

this engine hadn't been started in about 4 years, the owner said he parked it when it started making the woffing noise. i hooked up a electric fuel pump and a 5 gallon jug, turned it over several times and it fired up no woffing at first start. after running for several minutes, the woffing started again, if it is valve train, that should be pretty straight forward, pull the heads and rebuild them. i can buy this for like $100, it shows 86,000 on the speedo. are the 6.9 as good a engine as the 7.3? and should i plan on a complete rebuild?

 

[Diesel JD]

I'd bet its the lifters, based on what I've gleaned from reading here and over at TDS over teh years. To me teh 6.9 is as good or better than the 7.3. There tend to be less cavitation issues on the 6.9, although 7.3s also do well if teh additive is maintained. The power difference is very little. The 6.9 does tend to need a set of updated headgaskets at 100-200K miles. I would say if you do a correct head job, check the valves and replace any bad ones and change out the lifters you should ahve a good base to play with. No guarantees on that fuel system. Its been sitting and its gettinga few miles on it to begin with. The glow plugs were not as reliable on teh 6.9, but you can switch it over to solid state in an afternoon, or for even less time and effort set up a momentary toggle switch that will work flawlessly as long as you don't leave the plugs on too long.