Thunderclaps like Thor coming off throttle - leaky injector?

S

stuartinzg

Active member
Hi all,

As we all know the pops and bangs on overrun are a pleasant addition to the 35iS exhaust system, but recently I have noticed that with Sport mode enabled, under certain circumstances the car seems to call upon Thor who reigns down a mighty thunder clap. We're not talking pop-pop-bang-bang, we're talking almighty crack, to the point everyone within a 50 metre radius turns around to see who crashed.

I would say that it occurs most often when the car is around 90-95c oil temp, in sport or sport+ and manual mode. Accelerate to around 2-2500 and then back off the throttle.

At first it was quite amusing, now I'm considering if the cats and silencers are being mashed to pieces ...

How can you check if an injector (or injectors) are becoming "leaky" ?
 
Do you have white smoke from the exhaust when started from cold ?

Before all my injectors were changed due to a random occasional misfire with engine light from cold I noticed from a cold start there was a load of white smoke

Initially I thought it was steam however as soon as the injectors were changed this all stopped , the ticking noise when the engine is running which is common on the N54 went from quite loud and annoying to barely noticeable after the injector change

Any codes thrown up ?
 
On a cold start let your car run for 20seconds then turn it off, pull the spark plugs out and check if they are soaked in fuel. If so then the injectors are leaking.

But it's pretty normal getting a loud bang when backing off at those revs.
 
35i-Nut said:
Do you have white smoke from the exhaust when started from cold ?

Before all my injectors were changed due to a random occasional misfire with engine light from cold I noticed from a cold start there was a load of white smoke

Initially I thought it was steam however as soon as the injectors were changed this all stopped , the ticking noise when the engine is running which is common on the N54 went from quite loud and annoying to barely noticeable after the injector change

Any codes thrown up ?
Click to expand...

I didn't check for smoke. I noticed it's getting more and more ticky since I bought it - now on 29k miles (bought at 18k).

No codes yet
 
R.E92 said:
On a cold start let your car run for 20seconds then turn it off, pull the spark plugs out and check if they are soaked in fuel. If so then the injectors are leaking.

But it's pretty normal getting a loud bang when backing off at those revs.
Click to expand...

Interesting, thanks. I'll organise this at my friends shop. The pops are changing since I've owned it, becoming more aggressive, like unburnt fuel. If it carries on like this I'll start thinking I'm driving an RX-7 ...

Quick Youtube scan and I found something similiar! It's a bit like this (first pop as it drives away): https://youtu.be/QfHrAOJ26B4?t=1m10s
 
Mine used to do it,but it was hard to replicate it if you wanted to...lol..

It also did it sometimes on upchange at full throttle,a proper loud bang...I thought it was down to the mapping..
 
Mine let's out a huge bang above 4000 RPM when the throttle is above 60% on manual shifts and sometimes when jumping off a near WOT throttle above 4500 RPM.
 
I don't get the crack at your low revs Stuart, bangs and pops yes but like Techathy mine does it at approx 4250rpm, a loud gun shot, always at those revs.
 
You can also sometimes see leaking injectors in log data.

If you do a 10min log of driving around town with the throttle position and lambda AFR 1 & 2 logged you can look out for AFR readings while the throttle plate is closed. Normally the engine will stop all fuel being injected when the throttle is closed but if you have a leak then the bank will show fuel present.
 
R.E92 said:
You can also sometimes see leaking injectors in log data.

If you do a 10min log of driving around town with the throttle position and lambda AFR 1 & 2 logged you can look out for AFR readings while the throttle plate is closed. Normally the engine will stop all fuel being injected when the throttle is closed but if you have a leak then the bank will show fuel present.
Click to expand...

Nice one, I'll do this data log and then post it up see if anything can be spotted :thumbsup: R.E92 to the rescue again
 
john-e89 said:
I don't get the crack at your low revs Stuart, bangs and pops yes but like Techathy mine does it at approx 4250rpm, a loud gun shot, always at those revs.
Click to expand...

I'll see if I can do a Go Pro video this weekend :thumbsup:
 
You must log in or register to reply here.
Back
Top Bottom