Strange exhaust noise/vibration during heavy rain

[Mvy]

Hey folks,
Since supercharging the car, an odd issue comes up only when it rains really heavily and I am driving on a flat road. All of a sudden, I will hear a heavier exhaust noise, and when I modulate the throttle the higher the rps, the louder and more guttural the noise. In addition to the noise, i get a very odd vibration that resonates in the cabin under the driver footwell into the seat and drivetrain. As soon as I hit a hill or a decline, the noise clears. Its like water is getting into the intake somewhere and getting off flat surfaces helps it roll off.
Im pretty low suspension wise so I often wonder if that contributes to the water getting in somewhere. I also have an AFE 2 stage with the induction port closed(snorkle to hood vent) to reduce the SC whine.

I have a harrop supercharger so the whine you hear is not related to the issue. Its also raining like a mother so hard to hear over that. I tried to capture in the below video but its not great. It happens right at 5 seconds on the below video.

https://drive.google.com/open?id=1TM...dyS_6NguYIw16j


Anyone had something like this? Think its doing any harm?

[Mvy]

Bump, any ideas?

[M.Hagen]

Hard to discern the noise since there is no "dry" example, but I have a couple thoughts.

Does it sound like your cold start air pump is on again? I had mine randomly come on during last winter when driving (oil & water were at std temp). It was very obvious. I never identified a cause.

Do you have a P3 gauge or Awron? I recommend comparing AFR and ignition timing from dry driving to wet driving. Very rich and very lean conditions can cause audible changes in your exhaust tone. Same with ignition timing.

[Mvy]

Originally Posted by M.Hagen

Hard to discern the noise since there is no "dry" example, but I have a couple thoughts.

Does it sound like your cold start air pump is on again? I had mine randomly come on during last winter when driving (oil & water were at std temp). It was very obvious. I never identified a cause.

Do you have a P3 gauge or Awron? I recommend comparing AFR and ignition timing from dry driving to wet driving. Very rich and very lean conditions can cause audible changes in your exhaust tone. Same with ignition timing.

Its similar to cold start roughness, but only when pushing the throttle. Its so weird it only happens when it rains very heavily and at no other time. Its happened about 3 times now. The amount of vibration is much worse than typical cold start however and the fact it resolves when getting off flat makes me think its not the pump. I dont have a p3 or awron but I do have carly. Can I check with that?

[Bartledoo]

Originally Posted by Mvy

Hey folks,
Since supercharging the car, an odd issue comes up only when it rains really heavily and I am driving on a flat road. All of a sudden, I will hear a heavier exhaust noise, and when I modulate the throttle the higher the rps, the louder and more guttural the noise. In addition to the noise, i get a very odd vibration that resonates in the cabin under the driver footwell into the seat and drivetrain. As soon as I hit a hill or a decline, the noise clears. Its like water is getting into the intake somewhere and getting off flat surfaces helps it roll off.
Im pretty low suspension wise so I often wonder if that contributes to the water getting in somewhere. I also have an AFE 2 stage with the induction port closed(snorkle to hood vent) to reduce the SC whine.

I have a harrop supercharger so the whine you hear is not related to the issue. Its also raining like a mother so hard to hear over that. I tried to capture in the below video but its not great. It happens right at 5 seconds on the below video.

https://drive.google.com/open?id=1TM...dyS_6NguYIw16j


Anyone had something like this? Think its doing any harm?

Mine also did this back east in heavy rains, but not since I moved to Seattle since we never have heavy rain here. I never found a definitive answer. I figured it may be from rain accumulating in the air box temporarily. The first time I experienced it my only mod was welded test pipes.

[dparm]

If the car is stationary in the rain, does it happen when you apply constant throttle? This would rule out certain portions of the drivetrain causing the problem.

[Mvy]

Originally Posted by dparm

If the car is stationary in the rain, does it happen when you apply constant throttle? This would rule out certain portions of the drivetrain causing the problem.

Yes. When i noticed the sound, I pulled over still on flat. When applying constant throttle, the volume and amount of vibration increases exponentially.As soon as i get off level ground, it goes away in an instant.

[dparm]

Does it happen after you wash the car?

[Bartledoo]

Originally Posted by dparm

Does it happen after you wash the car?

Not for me. It only occurred during super heavy downpours. As soon as the rain let up it disappeared.

[Mvy]

Originally Posted by Bartledoo

Not for me. It only occurred during super heavy downpours. As soon as the rain let up it disappeared.

same here. I can't make it happen with a hose. I've tried flooding a bunch of spots. it's almost like I have to drive through high water ( an inch or two on the road) to get it to happen.

[Mvy]

Final Update:
I believe this issue is related to the center support bearing. I just replaced it. My suspicion is water was getting up into the drive train somehow triggering the terrible vibration I was experiencing. Ill post updates if it comes back, but so far so good.

[Mvy]

Ugg its back. Left at the shop, they could not find anything wrong. And of course the heavy rain stopped as soon as I dropped the car off. Its a mystery.

[Mvy]

Originally Posted by M3Post

Hhhmm.. IF water is getting past or through the air filter into the blower lobes that would be bad. Since water is incompressible. Check the filter and it's connection to the plenum snorkel. If any holes or if the junction between filter and snorkel are loose, you might have a situation where water inside the air box is being vacuumed into the blower. Just trying to help and think outside the box..

Thanks for this. The first thing I did last time was remove the air box cover. The good news is the filter was dry, not a drop of water on it or around it. As soon as the heavy rain stopped, so does the issue. So weird!

[Gregonater]

Any chance anyone has resolved this? Mine does the exact same thing but I have no supercharger.

[Mcte92]

You have an exhaust leak somewhere. S65 decel compression pulls air/moisture into your o2 sensors and takes a minute to correct

[cobrabooya]

Hey OP, did you find the solution eventually? My car had the same exact issue twice these few days at California. Only happened on freeway heavy rain.

[Mvy]

I did actually. Two things. I went back to the stock airbox. Next, I had blocked my hood vent (drivers side) to reduce my supercharger noise. It actually acts as a place for the intake to eject water when its raining. I see tons of water come out of it in the rain. Once I pulled that foam blocker I had made and put in there out, I have not had the issue since. Even in heavy rain. So that seems to have been it. If you have an aftermarket intake, or your vent blocked, this could be the problem.

[omgzirra_exe]

intake is just eating up rain water, you can alleviate the issue by just adding a rain sock over the filter.