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Discussion Starter · #1 ·
Twice yesterday! Started the car and heard a bang from the exhaust.

The only time it’s happened before was when I started the car after a period of no driving for about a week.

Unburnt fuel? Or something more serious

(I’ve got a full tank of the Tesco’s 99 RON unleaded)
 

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When I had my speedparts stg3 my car would 'bang' sometimes. Changing back to the Std ECU has removed the bang (and the thunderous performance )
Not sure what might have changed for you but I guess the uprated ECU must throw more fuel around.
 

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Discussion Starter · #3 ·
Yep, MapTun stage 3 ecu in the car at the moment so hopefully it's nothing too major.

thanks
Zahid
 

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I've had the same problem on & off in my 1994 CSE 2.3t for the last 3 years, and was told it was the DI on the way out - although the previous owner assured me it had recently had a new one. I understand that it could damage the cat, but AFAIK it hasn't damaged mine, still passes MOTs OK most recently a few weeks ago.
 

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Discussion Starter · #5 ·
hmmm, that's interesting as I've only recently put on a new DI. I also have a CAT bypass pipe fitted. However did have to put the CAT back on last week for the MOT, but have since changed back after the test. I hope it is'nt the DI as I'll be really peeved

Zahid
 

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Discussion Starter · #8 ·
before that it was a cat bypass and the bangs were much more frequent without the Cat[/b]
aha! Hopefully that's it then


My DI has nowhere near 15k miles on it, more like 2k!

cheers
Zahid
 

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Zars funny you mention 'bang' on start up my Aero has started doing the same more so when been left for a day or two I thought unburnt fuel!
It seems to have started not long after getting
3" down-pipe fitted
I also have had a new DI less than 2K ago.

The car drives fine so will leave it at that
 

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Discussion Starter · #10 ·
Oh mate, no probs there, plenty of
in the car

Just wondering whether I'd see something lying on the ground after driving off
 

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Mine bangs sometimes on start up (usually when warm) & I know others that do too. Common link is the JT exhaust. Not a major problem, but it tends to make people jump if I am at a petrol station!
 

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Nothing to do with cats or JT exhausts, I'm afraid - my Aero has always done it, through changes of:

standard downpipe/cat to abbott downpipe sans cat

standard centre box/resonator to oem absorption centre box

standard '97 VSS ECU to standard '93 non-VSS ECU to Stg3 Speedparts ECU

all kinds of petrol...

standard airbox to Speedparts open-cone-in-the-wing

DI pack change

Still scaring people at petrol stations!

The difference has been the change from 'Whummmph!' before modifications, to 'KABOOOOM!!!!' now that the intake/exhaust/ECU combo is in place.

When my little girl was at nursery, I 'flamed' on start-up once and left a big scorch-mark on their newly painted fence too - thankfully that sort of behaviour hasn't repeated (I think it was a death-knell from the DI pack).

Carl
 

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My stage 4 9-5 bangs and pops quite often when cold but is ok when warm, I have video's of flames shooting from my exhausts when it does it

Never did it as standard or even at stage 1 tune so I guess it must be over fuelling Forgot to mention it also does it after a short stop even when warm
 

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Surely the only thing actually causing the bang, whether you hear it or not, is excess fuel in the exhaust.

Doesn't this
A) ruin your catalyst(s)
B) fail your emissions test on high HC levels?
 

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It is usually caused from the way DI cars start up... when you crank it over, the ECU doesn't know if it is TDC for cyl #1 or #3, and #2 or #4, so it fires two cylinders at a time - untill the DI registers an ignition in a cylinder. If for some reason, it takes a little extra cranking, then some extra fuel will be in the exhaust, and if a cylinder fires at BDC, then it will have exhaust valves open, and you will get combustion (of unburnt fuel from cranking) in the exhaust manifold and exhaust, causing a loud bang in the process. I found that it happens on my standard aero if it turns over more than 3 times, but starts with the bang.
I have read this is a normal thing that you just live with.
 
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