What causes rythmic running?
 

A friend asked me go on a test drive of an 87sdl w/ him.
Car was great except for the idle was a bit lumpy and when cruising at around 2800rpm there was a rhytmic pulsing...not enough to affect accel or the tach but I could hear it.
I have a 350sdl and so that's what I am comparing it to.

Damned if I don't have the same thing bothering me on the '86 SDL.

It's been this way since I purchased it.

Seems to be dependent on rpm's........you only feel it above 2800 rpm.

And it's also dependent on load........you feel it when you apply more power.

It's a rhythmic droning........about 200 cycles per minute.........but after listening to it carefully for years now.........I'm leaning away from the engine causing it...........maybe driveline related??

I'm curious if a gasser would exhibit the same thing.

It has bothered me for quite awhile on the SDL.........I'm sensitive to it.

Do you not have this same result on the '90??

Could it be governor related?

It seems to bother Brian.:D I can hear it as well, at least I think I can, doesn't bother me.

Brian you need to listen to my SDL when I get it out of storage. Lots of driveshaft related parts are new, maybe I got rid of the noise?

He listens to his seats talk to him all winter long:eek: :rolleyes:

I don't know maybe I am used to it. Twin engine boats make the same type of noise when the engines sync up. I just don't hear it anymore unless I really listen.

Exactly. It sounds like two diesels that are out of sync by 180 rpm or so. I heard it on the '87 as well.

I need to drive yours and see if I notice it on that one. Seem rather odd.......can't figure out how its engine related.

My 90 doesn't do it on the road.
W/ temps below 25F, it'll do it at startup for 20 seconds or so.

That tells me that it's not engine related. If it was the engine, all of them would do it.

The startup issue is a separate issue. That's hunting caused by the governor.

But the 3.5 may have different balance than the 3.0.


Anyone w/ the 3.5 have this?
How about the 617s?

Yes, I suppose that's possible.

I did hear it once, recently, on the 617........very faintly......at one discrete rpm........very difficult to notice.

I had a gasser (don't tell anyone...Pinto) that would do something similar when running it near top speed of ~80 or so.

You can also hear it on twin engined airplanes like Beechcraft Baron and one of my friend's '95 S420, gasser. I'm guessing, its the electric auxillary cooling fan in front of the AC condenser. Does SD's have dual aux. fans? '95 S420 does have two aux. fans side by side, which kinda simulates the two propllers on twin engine airplanes.

No, it's not the fans. The sensation ebbs and flows when power is applied and removed. The SD has only one fan and it doesn't run with the exception of when the a/c is on.

If its not the fan, is it just te AC compressor cutting out and kicking on when desired temp is achieved depends on the temperature wheel setting?