Loud boom on hard up-shift?!

General General Lotus Talk
1

I�ve noticed a rather loud �percussion boom� at the point of up-shift through the gears and changing approx 6800 � 7000rpm.

I am used to hearing a few pops and bangs when I am decelerating and down gearing, but never had these bangs before on hard acceleration.

Is this normal? If so, what is the reason for this?

2

Dont know if it is normal but mine does it as well. It is flames exploding out of the exhaust . Take it you have a cat pipe and sports exhaust as mine doesnt do it with the cat in.

3

mine does that + 2 foot flame

4

Only time i have had that is when i have had to out of desperation fill up with bad fuel (low octane), it’s not the usual pop and bang, more like a platic bag being popped ? Try filling up with some good quality fuel.

At the risk of being laughed at i would go so far as suggesting that if it continues and never did it before, it could be the lamda sensor.

  • Sneaks off to dissapear into crowd inconspicuosly -
5

I only fill up with Shell Optimax which is the expensive higher octane stuff. OK�…what is a Lamda sensor and why are you sheepish to mention it? 

Carttman

6

I only use Optimax as well and it doesnt do it with the cat in - so I assumed it was due to having a straight through exhaust and cat pipe. I have the Eliseparts back box which is about as straight through as you can get!

7

You can make this happen if you “lazy” shift at about 7K when the exhuast is at a good temperature.

Seems to only work for me with Optimax or BP Ultimate and then only after a good thrashing so its nice and hot -

I do it deliberate when someone is a bit close …

If you shift faster or at higher revs it doesnt happen

My experience anyhow …

8

I tried it last night but to no avail… I’ll try the “lazy” shift and see if that works

9

My neighbour saw flames from mine 1/2 mile away

10

OK�…what is a Lamda sensor and why are you sheepish to mention it? 

Carttman

the Lambda sensor measures the oxygen level in the exhaust to make sure the mixture is optimum for the catalyst (but not optimum performance). If you have a cat bypass or computer that ignores the lambda probe it is irrelevant.

11

…so I guess most people with Exiges require Lamda sensors then?

Carttman

12

My neighbour saw flames from mine 1/2 mile away

That’s some palatial manor you have!

13

if only

LOL