Engine noise between 4K and 4.3K rpm - LotusTalk - The Lotus Cars Community
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post #1 of 4 (permalink) Old 07-10-2019, 06:43 PM Thread Starter
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Engine noise between 4K and 4.3K rpm

2008 Elise SC with factory sc, maps and everything engine-related.
I am hearing a metallic aluminum-sounding pinging noise that starts at 4000 rpm and goes away at 4300 rpm. Always and in any gear.
Checked for anything loose in the engine bay and exhaust mounts. Checked compression.

The engine feels fine but I am loosing power. Although I cannot feel power loss in my butt, at Palmer I am down 10 mph on the straight and 6-7 sec per lap.
This started happening after I had a minor fire in the trunk caused by exhaust heat. That was addressed by gutting the cat.

Is there anything special that is programmed to kick in precisely at 4K rpm and end at 4300?

Any other thoughts or suggestions?

Here is the sound: https://tinyurl.com/y6wkkrlt

Black/Silver 60th Anniv Elise

Last edited by artmt; 07-10-2019 at 06:57 PM.
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post #2 of 4 (permalink) Old 07-11-2019, 08:32 AM
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Do you feel a loss of power in that rpm range?
What was damaged in the fire?
I'm not sure how the stock ECU reacts without the cat in the place since it is looking for it with the post cat 02 sensor.
6-7 seconds per lap is a large loss of power.
Talk about a PSA for not running a cat on the track.

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post #3 of 4 (permalink) Old 07-11-2019, 08:58 AM
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Quote:
Originally Posted by ScottH83 View Post
Do you feel a loss of power in that rpm range?
What was damaged in the fire?
I'm not sure how the stock ECU reacts without the cat in the place since it is looking for it with the post cat 02 sensor.
6-7 seconds per lap is a large loss of power.
Talk about a PSA for not running a cat on the track.

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Fuelling only depends on the pre-cat sensor. The post-cat sensor only is there to check for the cat, so engine operation is unchanged.

OP, ten imaginary bucks says the cat originally melted and then caused your heat issue, so best case scenario is that you still have some precious melted bouncing around in the exhaust system somewhere, and you just hit a harmonic that excites it. Try taking the muffler off and shaking it and listen for a rattle.
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post #4 of 4 (permalink) Old 07-11-2019, 01:58 PM Thread Starter
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I did replace the main O2 sensor.
I can't say I feel any power loss specifically in the 4-4.3 range. At least not anything obvious.
The only fire damage I detected, aside from cosmetics, was melted taillight wiring in the trunk.
I also suspect that some junk was left over when may cat was gutted. It is just weird that it resonates with such precision and consistency.
Is it likely for that blockage to cause such significant power loss?

Black/Silver 60th Anniv Elise
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