isfvss

Can someone tell me why the ISF is LOUD at cold start for 30 ish seconds is it the exhaust valve being held open longer or longer duration ,to heat the cats up faster when cold for emissions, this is my guess, after a short time she goes a lot quieter, just interested cheers

Pushtape

lol look at tach and you'll notice the RPM is about 500 higher than normal. It is for warming up things. Also, if yours is LOUD you might have some exhaust mods?

isfvss

No its not cold fast idle I'm a 58y mechanic, it is a instant change of exhaust note not a drop in revs, every ISF does this on cold start.

mahcah

iTrader: (3)

The ECU runs open loop on cold start hence the initial higher RPM.

isfvss

Yep that's it open loop, still don't know why the exhaust note changes and the revs don't.30 seconds after cold start.

FFM

The tone change is quite wild. Especially with headers.

ISF5L

Like you mentioned earlier, every ISF does it. Its just more noticeable when you have an exhaust/headers etc.

I had always wandered this myself and did read about it. Cant remember where now that i want to find it but basically it was part of the cold start mapping of the ECU compensating for higher revs to minimise / prevent possible stalling.

Also had to do with the lack of heat in the engine on cold start ups vs once warmed up. Fuel doesnt burn as effeciently on a cold vs warm engine (lack of vaporisation) so the air / fuel ratio is slightly different on a cold start. Engine speed is higher at start to help burn the excess fuel thanks to ECU mapping and once the engine begins to warm up, excess fuel is dealt with, the air / fuel ratio leans back out to normal

tas02

iTrader: (2)

Because below a specified temp., both the direct and port injectors pulse.

lobuxracer

iTrader: (2)

It always sounded to me like it was oil getting to the top end. There's no way the exhaust timing can be extended or lift changed with the engine. The only thing the VVTi does is change relative lobe center to advance or retard the cam. Maybe, just maybe, it's because the locking pin in the exhaust cam is still in place and the exhaust cam timing is optimised for starting the engine, and once sufficient oil pressure has released the cam drive lock pin, the cam timing is adjusted for run not start. That would be my guess from having heard this many, many times.

Pushtape

Maybe I'm being ignorant here but doesn't every reasonably sized engine car have some distinct cold start noise?

jdmSW20

iTrader: (12)

Yeah I thought this was basically common place on cold start. My ISF does it and my old E92 did it as well, that car was hella loud on cold start and then would mellow out fast after about 20 sec or so. But that car had air pumps to warm up the cats on cold start so that's why it was loud on cold start(but it did sound beastly on first fire up haha)

lobuxracer

iTrader: (2)

GS F does it as well. I started the GS F last night to validate and woke up the wife at 1 am.

2008ISF

iTrader: (1)

Sounds like someone should volunteer and hook up to their car to watch live data on their tech stream software to see what’s really going on.

Any volunteers?

lawrence1

Could also be the air pump injecting air into the exhaust to warm up the cats faster? It is definitely noticeable.

lobuxracer

iTrader: (2)

What air pump?