Hello all, any help with this issue would be much appreciated, I am at the end of my tether!
I’ve had a rattling exhaust system for years, and finally replaced the downpipe with the mx5parts aftermarket stainless version. Also the manifold has had its heatshield removed, and is now wrapped.
The rattling has gone, but now at 2k revs and also at 3k revs, I get quite a high pitched high frequency pinging/ringing noise coming out from somewhere, and I cannot for the life of me work out what it is. It happens in every gear. It only happens when the car is moving, I cannot make it happen with the car stationary.
Against my better judgement I decided to farm this job out to my local garage, who I have always had a good relationship with. I called them and he said that it’s pinking, ECU can’t handle it, etc, which I just don’t believe, and also that I should ask mx5parts if there are any known issues. And of course when I spoke to mx5parts they blamed the garage for not fitting it correctly.
Feel like I am running out of options here! Any help or advice would be much appreciated.
hi Matt, that sounds really annoying especially as 3000rpm is around A road cruising speed. it sounds a bit like a frequency resonance inherent in that steel system. it puts me in mind of a former life in the brake business; when a disc brake/new pad squeal could not be tolerated we used to fit a shim behind the new pads & it changed the frequency of the squeal so that it was inaudible to the human ear. if you can’t think of anything else, try wrapping another part of the pipe to see if that does the trick.
it’s a bit like when you ping a glass held by the base it rings but not when you hold it by the rim.
sounds daft? maybe, but you never know until you try
From personal experience with past vehicles, I know just how annoying these sort of resonance noises can be. I’m with Joe on this one and ‘tuning it out of audible range’ is probably a worthwhile solution but can take a few tries to ‘hit the right spot’ with damping / lagging/ stiffness. Ultimately, ‘Tuned’ pipe lengths can work for you OR against you in the ‘chance world’ of exhaust systems and the possibilty of vibrating components in a CAT nowadays can add an extra dimension to the problem.
As you mention, it’s even more of a problem to diagnose when it doesn’t resonate at standstill but the clues are probably best covered by your ‘any gear’ observation & the two specific engine rev points that you mention which develop particular frequencies. However, it can sometimes become more of a puzzle when these things don’t follow a simple vibration frequency doubling pattern e.g. at 2,000 revs and then at 4,000… but harmonics do some strange things in complex systems!
One last thought, it might be worth trying it with a tankful of higher octane fuel just to eliminate the ‘pinking’ suggestion which can sometimes seem to be a bit of a ‘cop out’ with engine noises.
If its pinking, did this garage actually bother to check the timing? If its been advanced to 16 or 18 BTDC, as some people are known to do, it will pink with normal petrol. Bear in mind that the standard downpipe has a bracket connecting it to the bellhousing. I take it this MX5parts pipe won’t have that; aftermarket manifolds, which also don’t have this bracket, can sometimes sound a bit buzzy. MX5parts displaying their usual response to customer queries; blame someone else…
Thanks for the replies guys, yes the noise is very annoying, but I am far more annoyed that I took it to a garage and I’m still having to deal with problems. That said, I’m not sure I can blame them… (we’ll come back to this!).
I’m really glad you chaps are talking about harmonics/resonance, because that’s EXACTLY what it feels like to me, given that it happens at regular rev intervals, and only when car is moving (i.e. input frequency isn’t ‘correct’ when car is stationary). But I feared I was being biased (design engineer…).
I can confirm the bracket is missing! It didn’t fit (I did buy one, just in case). Maybe putting this in would be enough to change the mode and push the resonant frequency somewhere better, but hacking will be required. And tuning lengths etc also achieves this as you say.
Why would it suddenly start pinking, sounds like an utter cop out to me. This is just the last part of the system to be changed - the decat pipe, middle section, and rear section were all replaced a few years ago, never had a problem. Yes it was all stainless steel…
Nothing is blowing anywhere.
I need to admit something else… when I first picked up the car garage, I’m pretty sure it wasn’t making this noise. I made up all of the gaskets, which I provided to the garage. When I got the car back, I went under to check the work, and I noticed the gaskets and bolts that come with the downpipe had been used between downpipe and decat. I had provided all new stainless nuts and bolts, but they were not used in this location. So I changed the bolts, and while I was there, I popped my own gasket in. Maybe I should try swapping back to the one that was provided with the downpipe see if anything changes (I hope I can reuse this gasket without issue).
Sorry for the essay, but sort of thinking out loud here!
I wonder if this could be a mis-alignment problem., either with the exhaust components or, as you are hinting at, a gasket problem. If the pipes don’t line up, or a gasket isn’t sitting in the correct position, then you could be replicating the reed in the mouthpiece of a wind instrument. The gas flow through the exhaust is different under load than it is at idle, which is probably why you only get the noise when driving.
The musical connections raised a smile but reminds me that this possibly links ‘a bit too close for comfort’ to just what we might be up against. The reed is one very real possibility but the twin pipe tune is also along the lines of the principle we are talking about… ‘sounds’ (sad eh?) to me as if you might know more about church organ pipes than you are letting on Joe! (However, nodes and anti-nodes with harmonic frequency doubling at each octave is possibly a much deeper tone than this thread requires!) This all takes me back to building reverse cone exhaust systems in my early two stroke biking days & the need to reflect a positive pressure wave back up to the exhaust port at just the right timing point for peak power at a given rev range… ‘echoes’ of LJK Setright for those with a long enough memory!
All joking aside, the nuisance value of a resonating exhaust can be really annoying & the accidentally off-tuned lengths & diameters are fairly fixed factors when you have already built a system which is ‘singing’ at a given rev range… imposed by pressure waves which relate directly to load etc as suggested earlier up the thread.
One other thing that comes to mind, thinking back to one stainless steel exhaust that I had with nuisance vibration some years ago… the manufacturer had clearly chosen to use thinner material than would be used for a mild steel exhaust & thinner material might more easily vibrate and set up a sympathetic vibration… one cure might be to stiffen any thin section under suspicion, possibly by fitting the bracket mentioned previously or even by the addition of a jubilee clip (or two) around the outside… easy to adjust and slide along a bit if you think you might be getting somewhere with it.
As annoying as the noise might be Matt, there WILL be a solution, probably a simple one in the end… & like others, I’ll be interested to hear about the ultimate cure.
Please forgive my lack of reply, busy few months, and the exhaust was an ongoing saga. It’s sorted – will summarise briefly.
Gone day it suddenly stopped ringing. Few days later had a horrible rattle, almost sounded like a grinding noise. Weld had cracked on decat. Decided to get it welded up rather than replace. High pitched “ring” was back. This straight away said to me that it was definitely a resonance problem as we all suspected, as the cracking of the decat weld had effectively tuned the noise out. Few more weeks of putting up with it due to aforementioned busyness. Noise disappeared again – that’s right, other weld on decat had cracked. Committed now, so welded it up again. Ringing noise back. Then at some point when I just couldn’t take it any longer I fabricated a small aluminium bracket that effectively extends the factory bracket on the bell-housing, so that I could make use of the aftermarket stainless steel downpipe clamp that I’d bought. Ringing noise gone.
Thank you all for the replies, apologies again for not rounding this thread off sooner.