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  #1  
Old 09-19-2003, 10:25 AM
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Join Date: May 2003
Location: Central Florida
Posts: 31
Wierd Noise on 91 350 SDL

I have an odd noise on my 91 350 SDL and I need some advice on what it might be. When I am driving and I am making the engine work (RPM @ 3000) or 75-80 on the highway I hear a noise that I would think is a valve or rod tapping. But if I have the car parked and just rev it to 3000 rpm and hold it, the engine sounds fine. So this noise I am guessing has to do with either the transmission or something else just not sure what. I know describing a sound in writing is nearly impossible but if anyone can offer insight as to what may make an odd noise when moving I would appreciate it. Car has 138k on it......Thanks in advance for all assistance.......
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  #2  
Old 09-19-2003, 02:44 PM
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Join Date: Jun 2000
Location: SF Bay Area
Posts: 19,743
Can you replicate the sound by reving the engine against the brakes with the transmission in D? Don't do this for more than 5 seconds at a time and let it idle for a minute between tries. Otherwise you'll cook your transmission fluid.

If so, it might be rod knock. Not a good thing in any circumstance.

Could also be noisy lash adjusters or nailing. Do a search on these key words. Maybe try lifters in place of lash adjusters. You can focus on the Diesel Discussion forum.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD
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  #3  
Old 09-19-2003, 08:25 PM
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Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
Transmission mount gone soft will cause drumming on accleration. I'd check it, hopefully this is the case.

The 603 3.5L is known for bending rods, but if that is the case you will have a terrible clank and horrendous oil consumption with copious blue smoke.

A dull thump would make me think of the tranny mount, or possibly the center bearing mount going -- if that is the case, the floor pan will vibrate at the rear of the front seat. If you put you hand on the drive tunnel when it's making the noise and you feel it vibrating, it's the center bearing mount.

Peter
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