Exhaust making sound it shouldn't!

[Kathryn]

This afternoon whilst out driving in the rain my exhaust decided to make, I'm not very good at describing sounds, but a louder, more coarser sound not unlike a motorbike might make (whilst on a test drive later I thought it was doing it again until I saw an Impreza coming up in the lane beside me). The car also felt rough. No warning lights, all gauges looking normal, no apparent loss of power. I decided to turn round and go home, after about half a mile all back to normal and drove home fine. Running car on the driveway all ok. Sounds normal when I rev it, bit of popping at high revs as normal. My thought, water in the exhaust system? There were a lot of puddles (and hidden potholes -grr) about.
Went in had a cup of tea and decided to take her out for a run. (I soon regretted that, due to the impending darkness and p-ing rain!) All seemed ok (the aforementioned Impreza made me worry for a moment) until I was on my way back home, approaching a small roundabout at 20-30mph, went round roundabout and back to normal...until I was on the home straight, at about 50mph now I guess, noise starts again, car doesn't feel right. With no safe place to pull over I carried on and again after probably less than a mile (although it feels much further when you've got a problem) back to normal.
I've driven many times in the rain so I'm really not sure it does have anything to do with that. Any suggestions? Bearing in mind this damsel in distress can look under the bonnet or even under the car but probably not have a clue what I'm looking at/for!
Its a Piper 2.25 btw.

[tb10]

Hi Kathryn,

I occasionally have the same issue so I know what you mean. I 'believe' it is something to do with the Turbo / stuck actuator but I'm sure someone else will confirm this. Drive it tomorrow and it may have resolved itself and then it will happen again in a week or so!

Can someone please confirm?

regards

John

[dapinky]

Having done very little work on an S2 or FED model with some of the emission kit which is fitted 'extra' to the SE versions I'm probably unqualified to offer an accurate diagnosis...

...was the change in exhaust note related to throttle possition, engine speed or road speed? Accellerating , decellerating or constant speed?

Was the turbo boosting at the time?

My initial thoughts are possibility of the innards of either the main cat or pre-cat rattling around inside the metal can and disturbing the exhaust flow, causing resonance - but hard to say without a look/listen.

[tb10]

Hi Dave,

What I get is the same result as when a rev limiter kicks in so the car will bounce off the limit determined by the turbo 'trying' to boost. It occurs just before the turbo kicks in and makes a raspy noise and won't accelerate. if you don't use the boost then the car drives fine, albeit, in a pedestrian way (for the M100!).

As sated above the next day when the car is driven it is fine.

It usually happens after the car hasn't been used for a few weeks.

regards

John

[Kathryn]

Dave, I think it may start under acceleration, but it doesn't stop under deceleration, gear change or anything. Not boosting at the time, and at different speed. I don't know how it first started as I had the radio on and the road wasn't exactly a smooth road. I heard it but at first thought nothing of it as the Elan often makes odd noises, it was only when I realised that it was the car feeling rough not the road that I realised something wasn't right. Second time may have been after gear change, but third time I was just going along, maybe accelerated slightly, can't have been doing any more than 50 if that, I was concentrating on the road, it was dark, rain was pouring and there were bright oncoming headlights!

John's suggestion sounds easier to resolve. Does that mean the wastegates stuck again? because I was actually wondering if it might be last week when I seemed to be getting less boost than I'd expect.

Might be worth mentioning she was parked up for 4 weeks until a fortnight ago and I've only driven her a few times since.

I guess I'll have to take her out again and see if there is a pattern but it won't be til next weekend.

[Kathryn]

Hi Dave,

What I get is the same result as when a rev limiter kicks in so the car will bounce off the limit determined by the turbo 'trying' to boost. It occurs just before the turbo kicks in and makes a raspy noise and won't accelerate. if you don't use the boost then the car drives fine, albeit, in a pedestrian way (for the M100!).

As sated above the next day when the car is driven it is fine.

It usually happens after the car hasn't been used for a few weeks.

regards

John

Hmm. Not sure that's my issue then. I have no loss of acceleration when it's doing it. Now I'm overthinking... Did I ease off the accelerator as a reaction to realising something was wrong - quite possibly. But I can then still accelerate. I can't make it go away it does that itself.

[dapinky]

Again, I'm leaning more towards an issue with the exhaust being partially blocked by something within the precat, main cat or silencer......

...... I would expect an issue with the wastegate to cause issues more the other way - ie, overboost as the excess gas can't escape if the wastegate isn't opening.

But If it isn't closing fully, it could give you a constant bleed of boost - but not sure if there would be an increase in noise as there would be the same volume of exhaust gasses passing through the system, just by a different route (but that would cause it's own noise because of fluid dynamics/cavitation!).

So, basically, I'm not really helping a lot.

Maybe someone who has experienced the pre cat honeycomb breaking up will be along to comment on it's symptoms to help limit posibilities.

[Elanlover]

Regarding Dave's comment on the cat and precat, how old are they? Are they the originals (hopefully not) or a replacement? The cat itself can be replaced with a current model but the precat needs to be a Lotus part I believe. So, if it hasn't been changed its very possible its broken up and clogging the exhaust. Compounding the problem would be the possibility that some of it has moved through the system and clogged the main cat or other exhaust areas. If at all possible, tapping on the precat and exhaust plumbing might reveal some loose bits rattling around in there. When mine broke up I experienced very inconsistent performance depending on where the bits where at the time I stepped on the gas.

Assuming there's a cat and precat on UK cars??????

[Simon_P]

I have the Piper 2.25 system with cat on my S2.

I was driving along on a cold wet night, I drove through a deep puddle/pothole and the exhaust made a hell of a racket. I thought something had come detached, so I pulled over to have a look, as I pulled over it stopped making the racket, I had a look and couldn't see anything wrong.

By the third time it happened realised that it only happened when I drove through deep puddles
The cold water gets on one part of the exhaust causing it to contract which makes the system bend enough to touch the chassis. When it heats up again shortly afterwards, it straightens and stops touching the chassis.

Test the theory by driving through deep puddles. - Cure it by avoiding deep puddles.

Also check the rubber hangers if they are tired they won't hold the exhaust in the correct place.

I would describe the noise as similar to someone drilling concrete in the room next door, the sound goes through you and around you but is exhaust noise rather than a drill noise. You also get a strong vibration - so all in it sounds like the exhaust has come detached and feels like the bottom has fallen out of the engine.

[tb10]

@Simon;

hmmmmmmmmmm Interesting thought........

[Kathryn]

Simon P, it did feel like a vibration certainly and water was my first thought but it's not happened before and I drive in all weathers! I don't recall going through deep water when it happened, but I had been through a rather large puddle earlier. And there was lots of surface water on the road.
I do hope it is something like that and not the pre-cat. The exhaust and cat were new in 2011 (I've found out the invoices) but the pre-cat isnt mentioned so I guess that is older.

[Simon_P]

Hi Kathryn,

On and off I have used my car daily, in all weathers, I've driven across Europe in summer and winter, snow, torrential rain, and heatwave - These days I would avoid driving it when there is salt on the road only because the bits that go rusty are the expensive bits!

This has happened to me 4 times, twice in the same place. When I say deep water I mean large puddle - enough to splash. I fitted the Piper exhaust myself in 2009 and it is excellent, and the clearance seems good. I think the rubber hangers get tired after a few years which allows it to happen - First happened to me in about 2012.

I wouldn't worry about the pre-cat. It is ceramic and almost indestructible, mounted in mesh, and housed in cast iron - You would have to try to break it directly with a hammer or something similar. After 21 years and 98k miles in my car I cut through the cast iron housing with an angle grinder to take the catalyst out (cos a new one is about £300), and then pressed it into a new housing (using a 12 ton garage press) and it is undamaged. There is no reason for it to break, it can't go anywhere, and if for some reason it did disintegrate you would have a permanent problem.

[Kathryn]

That's reassuring to know Simon. I'll have to see what happens at the weekend, but I don't plan to deliberately drive through deep puddles!
My dad suggested I take it up 'the exhaust place' , once I'd established where he meant I decided I might actually do that. They were brilliant a few years ago when I had a ridiculous quote from Seat for suspension bushes and wheel alignment on my first Ibiza, turns out I had unevenly worn tyres!

[Elanlover]

I suspect that your precat would likely be the original one. If so, that might be the culprit as they aren't meant to last 20+ years. Many of us got in on a "pre cat eliminator" group buy a few years ago. It was a part to replace the pre cat with a simple piece that was hollow with no catalytic materials - a pass through. The turbo spools faster and I haven't failed an emission test yet. In lieu of the pre cat eliminator some did it the old fashioned way. They removed the pre cat assembly and just hammered out the catalyst material before reinstalling.

[lotusflasherman]

That's reassuring to know Simon. I'll have to see what happens at the weekend, but I don't plan to deliberately drive through deep puddles!

Good plan. Quick way back to my village when travelling from the west involves a lane with a ford which is usually a shallow 'watersplash'. I'd had a nice cross country blast in my first SE and found it looking quite a bit deeper than usual but decided the alternative route would take longer so went through. Simon is correct about thermal contraction as the down pipe fractured just below the weld onto the triangular flange and I came out with an open exhaust just below the turbo - that really was an "Exhaust making sound it shouldn't" .. Drove a mile home making a lot of noise and removed it welded it up and put it back. That took a lot longer than taking the detour.

[Simon_P]

Elanlover,
I appreciate that you are the other side of the pond so actually have a Cat, but most elans don't so pre-cat eliminator is a figure of speech. I believe those that did hollow out their Cat did so (however misguided) in search of flow, rather than of necessity.

The ceramic substrate, where fitted, should be good for 200K miles.

[Elanlover]

Elanlover,
I appreciate that you are the other side of the pond so actually have a Cat, but most elans don't so pre-cat eliminator is a figure of speech. I believe those that did hollow out their Cat did so (however misguided) in search of flow, rather than of necessity.

The ceramic substrate, where fitted, should be good for 200K miles.

I didn't think that UK versions came with a cat but I couldn't recall. As for the catalyst material inside, mine certainly didn't last 200K miles. Not even close.

[Saltire]

Elanlover,
I appreciate that you are the other side of the pond so actually have a Cat, but most elans don't so pre-cat eliminator is a figure of speech. I believe those that did hollow out their Cat did so (however misguided) in search of flow, rather than of necessity.

The ceramic substrate, where fitted, should be good for 200K miles.

I didn't think that UK versions came with a cat but I couldn't recall. As for the catalyst material inside, mine certainly didn't last 200K miles. Not even close.

Kathryn's is an S2 like mine, with factory fitted cat and O2 sensor.

[Kathryn]

Kathryn's is an S2 like mine, with factory fitted cat and O2 sensor.

It is.

I looked up the previous owners posts and as I thought it is the original pre-cat.

Im hoping these chaps will be able to take a look at the weekend www.bell-silencer.co.uk/exhausts.html. I'm pretty sure they'll find what's wrong.
I'm hoping it's nothing worse than a loose bracket, but let's assume it is the pre-cat, what would my next course of action be? I've read up on it and it looks like hollowing it out is the cheapest and easiest option, but I sense some controversy!

[Elanlover]

There shouldn't be any controversy (really). The precat is there to assist in passing emissions testing especially when the engine is cold. I'm not sure what the deal was back when the car was built and the Isuzu engine was chosen but it apparently was borderline on some testing when cold. in my case, since removing the pre cat altogether I've not failed a test (your mileage may vary). With a reasonably new, modern and working main cat you should be fine. Hollowing it out is the simplest way to deal with the issue if it is the precat. You may find that turbo lag decreases because of it.