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Discussion Starter #1
Hi all, hoping for some pointers - I know rattles are extremely difficult to troubleshoot over the internet but I've got one that's concerning me a little bit.

Car is a 2006 Exige S, modifications include 2bular full system, proalloy charge cooler and recently has been tuned on an ECUMaster ECU. After collecting the car from the tuners I was unable to drive the car hard for a while due to a combination of weather and being away from the car, but this weekend I finally got to rev it out and although the car pulls great - there's a pretty nasty rattle at 7.5k RPM.

It happens in any gear, and can also be reproduced in neutral with the car stationary. At 7.5k revs the rattle starts, it sounds quite harsh and metallic and then if I let the revs drop down again, it fades again once dropping beneath 7500.

The new ECU has some pretty detailed logging, from what I can see everything looks OK in terms of fuelling, AFR, etc. No alarm bells running at all, the knock sensor is picking up the sound but the tuner has seen these logs and suggests it's just picking up the background noise (whatever it is) that's causing the rattle, rather than it being legitimate knock.

Obviously I'm sending as much info to the tuner as possible, so if there's an issue introduced by the map I'm pretty confident we'd have found it by now - I'm hoping this is just a secondary issue of something that's loose or has been disturbed as part of the install (or something that's happened coincidentally).

I've ruled out some obvious things as follows:

  • Undertray and Diffuser, both have been removed from the car and rattle remains.
  • All accessories incl. supercharger, ran the car without belt for a few seconds and rattle remained
  • Most heatshields are missing from the car already, so frequent offenders such as the 'U bend' one and manifold one are missing due to the 2bular.
I've had my wife rev the car on axle stands whilst I tried to pinpoint a location, all I can conclude is that the sound seems easier to hear from high up and impossible to hear when laying on the floor due to the other noise from engine/gearbox/exhaust etc at 7k+ RPM. The sound is easily most audible from inside the cabin, and sounds like it's coming from the engine bay - though I know how misleading sound sources can be in these cars!

I'm really running out of things to isolate/troubleshoot - I've gone made with cable ties to try and arrest anything that may be loose or dangling, I've been around everything I can access with a rubber mallet and I'm starting to fear that the sound is internal, which I presume to being serious!

I've taken a few videos, but the one which does the sound the most justice is this one:

If anyone has any pointers of things I can isolate/rule out, I'm all ears!
 

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Have you inspected the valve-train lately (check for cam wipe, 'lift bolt' locking pin fidelity)? It looks like your troubleshooting technique is logical so far.

It sure is uncanny how the sound is so strongly coupled to that engine speed. That makes me want to start by looking at parts that are tightly coupled to the engine (i.e. not damped by the engine mounts). I know you said that the sound is easier to hear at the top of the engine, but the sound is plausibly similar to a loose nut or crack in the exhaust; have you gone around and inspected exhaust and it's connections? I'm grasping at straws here.
 

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Discussion Starter #3
Thanks for your thoughts, seems we're along the same lines!

I did the lift bolts/cam inspection over winter but I've had the cam cover back off tonight for a sanity check. I know at least one person that had a (dealer fit) lift bolt come loose and fall out some months after fitting so that had me paranoid!

Needless to say the valve train looked fine to my novice eye.

Next up I took the backbox and cat section off, they're 2bular items fitted about 2 months ago so as expected they seem fine. There was however a bit of a creak from the donut/spring joint when tugging on the exhaust so perhaps a slightly better fit can be achieved tomorrow when I have the energy to refit it... I've not removed the manifold but I'll tweak up it's bolts tomorrow.

I've identified two possible contenders along my way but both seem to be a very long shot:

1) least likely the S111 catch cans bracket was just the wrong side of hand tight to the head, so these have been nipped up

2) bit more potential but the base of my charge cooler header tank (mounted to UK driver side rollhoop support, so right behind the driver) was interfering with the top of the solid breaker pipe that comes out of the cam cover just above the supercharger nose. Witness marks on both show they've been touching so this is definitely a good thing to fix but I've talked myself out of it being the issue I'm hunting just because I can't imagine it making that sound so reliably at that specific RPM... I have my fingers crossed that I'm proven otherwise tomorrow when I reassemble the car. The breather pipe moves with the engine of course and the header tank is static to the chassis... So just maybe!

In terms of internal engine issues, I'm trying to talk myself into the fact I'd feel an issue with power delivery if this was serious... Too naïve?!
 

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As long as you have the exhaust partly loose is there anything in it that rattles?
Loose change in the cabin? Throttle cable and shift cables all attached well? Check all pulleys for play?

Does the sound go away above 7500 or does it stay all the way up to redline?
(edit: I see your shift light also comes on at 7500)
 

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Discussion Starter #5
As long as you have the exhaust partly loose is there anything in it that rattles?
Loose change in the cabin? Throttle cable and shift cables all attached well? Check all pulleys for play?

Does the sound go away above 7500 or does it stay all the way up to redline?
(edit: I see your shift light also comes on at 7500)
Thanks for the suggestions, all pulley's seem fine (isolated by removing aux belt) but I do need to double check the crank pulley bolt.

The sound continues above 7.5k, when you're properly "on it" you can't actually hear it until you let off the gas, so I initially associated it with the gear change (dodgy synchro for example) but I've since ruled that out is it happens in all gears and neutral.

The shift light observation is interesting, I'd not noticed that but in hindsight I can't even remember when the light is supposed to come on despite having a couple of 2zz Lotus cars since 2016! This may be coincidental, but is probably worth mentioning to the tuner to see if it's a response from the new ECU.[/QUOTE]
 

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Discussion Starter #6
Bit of an update on troubleshooting...

Had manifold off and found evidence of slight exhaust leak at the gasket, fixed that but no change unfortunately.

I found a YT video of an MR2 w/ 2ZZ that had an almost identical sound coming in at 7.5k rpm, his problem turned out to be lift bolts (or at least, something that caused lack of high profile cam) and the sound was the sound of his lower lobes operating at high RPM. I've had my cam cover off once, but think I need to double check it all.

I know my cam activation is working because I can hear it, feel it and the car made good power on the dyno just a few days ago. It also logs on the new ECU so I can see when it comes on (and stays on).

I'm almost sure I've ruled out everything external to the engine now, but then again I guess I can never be certain.

Can anyone suggest any good tests or checks to do with the cam cover off? I know what a wiped cam looks like (I Think?) and I know to check lift bolts... but that's about it!
 

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Discussion Starter #8
Thank you, that's a useful link! I don't see any red flags based on what I can see under my cam cover though, shame!
 

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Discussion Starter #9
Happy to say I've resolved the issue, or at least.... worked around it for now.

It's all related to high-cam activation (just going to call it vtec as it's quicker...). Somebody commented that my car sounded exactly like theirs did when their 2zz vtec failed to activate, the low lobes at 7.5k and above just can't hack it (valve bounce? No idea) and so the car sounds very rattly.

I checked the config on my new ECU and sure enough it has parameters for VTEC activation, it requires 4900rpm, 50% TPS or above and 50kPA MAP or above. The first two are easily achieved on axle stands, but the car makes no boost when not under load... so all the testing I'd done on axle stands was not engaging VTEC and was the probable cause of the rattle...

But I still had experience of this rattle whilst under load, so I developed another theory. I watched back some gopro footage and noticed that you couldn't hear the rattle whilst accelerating, only whilst deceleration or during a gear shift. What happens on both of those occasions? You lose TPS and MAP... I checked the logs and yep, VTEC was dropping between gear shifts meaning that the small lobes were being thrown into the action at high RPM and was generating the rattle.

I made a quick change on the ECU to ignore TPS and MAP for deactivation of VTEC and voila - problem solved.

Obviously I have some follow up questions with the tuners, did they forget to configure this? Or is it supposed to drop VTEC between gears and mine is just unusually rattly on the low cam? Either way, car feels/sounds much better now so I've relaxed big time!

Before I changed the VTEC parameters:

Afterwards:
 

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Great detective work!
 

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The only reason I can think you would intentionally drop the cam like they had is to increase engine braking, but there's already more than enough of that with our platform. Good job! Check your overrun fuelling parameters in that region as well and make sure that, when spark and fuel are active, you have a reasonable AFR. Being port injected, you want the injectors to stay on during overrun to help with response, especially when blipping downshifts.
 

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Discussion Starter #12
Thanks guys, good pointers on the AFR. I had a wideband fitted into the manifold as part of this install so I've got all the data to check - will give it a scanning over later today.
 
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