Odd Behaviour

[Polabear]

Ok Guys,
This is mainly aimed at the owners with M/T as I have no experience of it happening in an A/T car. After driving along sedately (some of us do..... :rolleyes5 ) at around 30-40 in 3rd or 4th gear then floor it in 3rd or drop it down from fourth I get a loud pop/cough/spit from the exhaust, heard mainly under the floor. My question to anyone who may know is, is this the product of reigniting fuel vapour rich exhaust gasses which are left in the exhaust tract from driving gently then hoofing it,,,,or am I looking at a potential problem.

[wirdy]

Mine doesn't do this :headsc:

Did it start post boost controller fit?

I have noticed initial overfuelling from BDA's & interlecs exhausts when I've been following them just as they boot it - quite normal, I'd say.

[Legnum Boy]

Try this....

Drive along normally, when running at nominal temperature, pull in and get some more petrol...

When you get back in the car, as you start it up, floor the pedal, just for a second, and you will get numerous pops and bangs. :-D

Great for scaring the carp out of anyone on the forecourt.
Not so sure about the detrimental effect on the Cat. though.... :rolleyes5

Its defo an overfuel, re-igniting somewhere in the zorst.

[nick-f1]

Mine doesn't do that either Sean, so must be boost controller? overfuelling related I should think. I've noticed the same as wirdy as well.

Nick

[valmes]

Do you have boost controller fitted? Have you upped your boost?

I think that effect is called "fuel cut"... nothing to worry about. When flooring from low RPMs you get short boost spikes, and as a result - fuel cut, since it takes time for boost controller to stop turbos from producing needed amount of air flow to the engine. The problem is that BC see the mainfold pressure, and while your mainfol could be 99% full of pressurized air... your turbos still work and overboost since solenoids of BC work with air and can send signal to your turbo wastegates only by air hoses... ! Some can compensate for that, some don't. HKS FCD can help you get rid of it(fuel cut) , but use it only if you have some way of controlling fuel mixture to compensate for lean condition... since FCD changes voltage from Mass Air Flow Sensor to trick ECU...

One way is to get an adjustable FPR. Set fuel pressure at Fuel rail at about 2.9-3.0... Stock is 2.7 at idle. That should do it. Wide Band Lambda Sensor is a "must have" to do tricks with boost and fuel.

Hope this information can help...

[Spirit]

It's definately not fuel cut - I m still sure it is just overfuelling.

[Legnum Boy]

It is a trait amongst all turbo-charged cars. Im pretty sure that its excess vapour igniting on the heat of the turbo...
My old 200sx used to do this to order, especially on over-r.

[valmes]

Overfueling from what?
Standart fuel maps are very good in getting right amount of fuel!

There can be a problem with overfueling if you have fitted aftermarket Blow Off Valve(which is releasing excess air to atmosphere rather than back to the system). Then you can get "rich" and will get same effects...and a black smoke from your exhaust...

[Polabear]

Ok sussed it, its definately a boost thaaaaang, turned my boost controller off today and just ran with stock boost..Et Viola.. no more spitting and farting.... :rolleyes5 thanks all for your input.... :-D