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E86 change in behaviour after heavy rainfall drive. FIXED.

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Meds
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E86 change in behaviour after heavy rainfall drive. FIXED.

Post by Meds » Mon Apr 29, 2024 4:48 pm

Hey guys, I'd like to run something by you'll.

On the way to Ultimate BMW on Sunday were in a little convoy, battling horrendous road conditions from the rain.
Loads of standing water but I was avoiding it, not running through any obvious puddles.
1hr in my car started to sound like the centre section of exhaust had fallen off.
It was really loud, and the car felt a little sluggish. It sounded horrific.
Very noisy blowing/booming from underneath.

We stopped and checked (in the pouring rain damn it), the exhaust was present. :rofl:
Popped the hood, and it was deffo a very loud blowing/puffing noise when revved, and the revs felt sluggish, coming from under the drivers footwell area.
Not anything mechanical from the engine, no knocking, ticking or rumbling.
No engine check light, no steam or smoke.

Within 5 mins of setting off and driving slowly to the meet-point, it was back to normal. The glorious straight 6 sound track returned and the car response was normal.
All was fine on the next drive from meet-point to the show.
All was fine again when driving home, no issues and the car performed perfectly.

Until...... Another long stretch of standing water. A couple of inches deep for probably 20mtrs.
We drove through it very slowly (3mph max) and halfway through, instantly the car returned to sounding like the exhaust had fallen off.
Same symptoms, rediculously noisy, exhaust related, it was blowing/coming from underneath.

Within 5 mins the noise went and since then it's been running like a dream.
I took her out again today and no problems at all, running perfectly.

What could cause this, water ingress into the cats/sensors??
It honestly sounded/felt like I'd expect if the exhaust was filled up with water. But if water ingress to this extent was occuring, I'd have an obvious blowing exhaust.
Last edited by Meds on Fri May 03, 2024 10:11 am, edited 1 time in total.
E86 3.0si - Koni, Eibach, Eisenmann. Here:>> viewtopic.php?t=143973
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E86 change in behaviour after heavy rainfall drive.

Post by enuff_zed » Mon Apr 29, 2024 5:06 pm

Sounds a bit odd, but I remember back when I was a lad, my Dad had a Cortina Estate. That did exactly the same thing, except it sounded around the back box. Never did work out what it was, other than guessing water was getting trapped then boiling off, but that wouldn't explain the sluggishness you're getting.
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E86 change in behaviour after heavy rainfall drive.

Post by j3nks79 » Mon Apr 29, 2024 5:20 pm

Replace the downpipe gaskets.
I’d guess the cold water contracted the hot metal causing the blow
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E86 change in behaviour after heavy rainfall drive.

Post by Pondrew » Mon Apr 29, 2024 5:27 pm

j3nks79 wrote: Mon Apr 29, 2024 5:20 pm I’d guess the cold water contracted the hot metal causing the blow
That is a very good shout. :thumbsup:
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E86 change in behaviour after heavy rainfall drive.

Post by colb » Mon Apr 29, 2024 6:11 pm

Are you sure the downpipe joints are intact, failed gaskets there could be a possibility but I would have expected a continuous blow if that was the case. Just seen j3nks79 has posted same suspicion.
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E86 change in behaviour after heavy rainfall drive.

Post by Meds » Mon Apr 29, 2024 8:36 pm

It sounded horrific. But not misfiring from what I could tell as I couldn't feel any lumpyness and no EML.
Maybe the sluggish feeling was just me not daring to press the pedal too much in fear of what was happening.
I've been out again tonight and no issues..
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E86 change in behaviour after heavy rainfall drive.

Post by Meds » Mon Apr 29, 2024 8:38 pm

The downpipe gaskets are the 2 joining the headers to the mid pipe section?
Not the exhaust headers to the block?
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E86 change in behaviour after heavy rainfall drive.

Post by j3nks79 » Mon Apr 29, 2024 9:21 pm

Manifolds to mid-pipes yes. just under your feet
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E86 change in behaviour after heavy rainfall drive. FIXED.

Post by Meds » Fri May 03, 2024 10:10 am

The symptoms progressed, earlier in the week I started to notice some whistling from under my feet on engine braking, around 2k rpm. A blowy whistle, almost a squeal.

I took it in to my guy yesterday, he found the gaskets and flanges were falling apart, corroded.
The studs were grinded and drilled out, flanges cleaned up and new gaskets installed.

Loads better. Fixed (at least the 2k rpm whistle).
It's actually quite surprising how much now the exhaust noise is at the rear of the car, rather than escaping from underneath. The car sounds much nicer and fruitier from the rear pipes now.

Lets hope this was the cause of the sudden behaviour change that occured those 2 times after standing water.

Thanks for the advice, guys. :thumbsup:
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E86 change in behaviour after heavy rainfall drive. FIXED.

Post by coldel » Fri May 03, 2024 10:54 am

Good to hear, and great knowledge guys :thumbsup:
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E86 change in behaviour after heavy rainfall drive. FIXED.

Post by colb » Fri May 03, 2024 7:45 pm

Those exhaust flange studs rust away to nothing and are a pain to get out. There is a thread of mine showing how to by slotting the flange hole to release pressure to get them out. Replaced mine with stainless nuts and bolts.
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E86 change in behaviour after heavy rainfall drive. FIXED.

Post by Meds » Fri May 03, 2024 8:00 pm

colb wrote: Fri May 03, 2024 7:45 pm Those exhaust flange studs rust away to nothing and are a pain to get out. There is a thread of mine showing how to by slotting the flange hole to release pressure to get them out. Replaced mine with stainless nuts and bolts.
That's exactly what my guy did. A slot to help get the studs out, then replaced with stainless.
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E86 change in behaviour after heavy rainfall drive. FIXED.

Post by Mr Tidy » Fri May 03, 2024 8:06 pm

It's good to know you got it sorted. :thumbsup:
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E86 change in behaviour after heavy rainfall drive. FIXED.

Post by colb » Fri May 03, 2024 8:43 pm

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