1985 Eldorado Exhaust Drone

[jgalin]

I am wondering if the drone noise that I am hearing from my 1985 Eldorado is typical for that car/engine.  Under steady acceleration the car sounds normal but as you ease up on the accelerator there is an exhaust drone noise that is kind of annoying.  Both the catalytic convertor and muffler appear to be new(ish).  I had the same issue on my 1984 Eldorado.  I replaced the resonators on that one but it did not change the exhaust tone.  Just wondering if others have encountered this and whether it is normal.  Thanks.  Jim

[TJ Hopland]

The ease up part is what I'm keyed in on.  That makes me think the diverter valve on the AIR (smog) system isn't working so its still pumping air into the exhaust on deceleration.  I think the 80's would have a dual valve assembly.  One valve chooses if the air goes to the cat or to the exhaust manifolds and the other valve chooses between the first valve or bypassing the air I think to the main air cleaner housing.

The computer cars like this the valves are vacuum actuated but electrically controlled by the computer.  What usually kills them and eventually the AIR pump is the check valves fail and let the corrosive and hot exhaust gas backfeed into the system.  The check valves are those nut fitting looking things usually at the joins between the metal lines and the hose sections. To check em just disconnect the hoses with the engine running.  If you get exhaust they are bad.  They are a fairly universal part you can still get.  To remove old ones I have found you usually have to get a small cutoff wheel like a dremel style and slit the nut part so you can split it.

If the main valve has been damaged or failed good luck finding a replacement one of those. I don't know if aftermarket ever made those and when delco still did they were kinda expensive.  The 02 sensor is downstream of the manifold injection point so not having it work correctly could effect how the computer is trying to run the engine. Most of the time air is being injected so having it stuck on means things are mostly normal.  If you were to disable it so it wasn't injecting the air that should fix the decel issue but may confuse the computer during cruise and idle which long term won't be good.  IIRC I think you end up running lean and that results in things like burnt valves and rings.

[smokuspollutus]

The walker exhaust systems currently available will cause horrendous drone if you combine the SoundFX muffler (only one available) with the Quiet-Flo resonator. It can be minimized using a Soundfx resonator (at the expense of a slightly louder exhaust burble)

You can read about it here:


https://www.cadillacforums.com/threads/puttin-on-the-ritz-1984-eldorado-biarritz-project-thread.885466/post-16300225

[jgalin]

@TJ Hopland and @smokuspollutus Thanks much for the helpful replies.  I don't think there is anything wrong with how the exhaust system is working.  I believe that the replacement muffler and resonator combos that are currently on the car are incorrect. 

@smokuspollutus Do I only have to replace the current muffler with the AP MSL series, or do I have to address whatever resonator is on there as well?  It sounds like I need a QuietFlo resonator.
Thanks
Jim

[smokuspollutus]

Yes, the MSL muffler should basically eliminate the drone.

[jgalin]

Thanks much for the help!

[jgalin]

Unfortunately, back to square one.  MSL 700059 is nowhere to be found.  I can find Sound FX all day long.  Any further suggestions would be appreciated.

[smokuspollutus]

That's discouraging.

You can use the SoundFX muffler with a matching SoundFX resonator and you should not have the drone. It is the combination of the SoundFX muffler and the QuietFlo resonator that creates the drone for some reason. Good luck!

[DHeins]

Struggled with the droning that came from resonator. It was a frequency that drove me nuts. Tried two different versions of aftermarket resonators and still droned. Decided to try some mass dampening by using rubberized magnetic strips.  Kept adding and adding until able to change the frequency. Now it's down to a nice hum. Never goes away but at least it doesn't have that annoying drone sound.  No need to worry about temperature as the exhaust never really heats up that far back.