-ant-

just wonderd is to ok to fit a fuel cut defender to a scoob, does it not cause any problems becuase my knowledge is they mod the signal to ecu but wouldnt this make the ecu think the the car is running diffrent boost and cause det.
Want to get one because when its cold in 3rd mainly gear it spikes alittle somtimes and going between warrington and burtonwood the ground leval changes . The car spikes a bit more in in burtonwood than it does in warrington and it changes in diffrent parts of the town, just cba with it fitted a mbc to have a bit more control and i do but its pissing me off now lol

sponners

iTrader: (4)

yeah, it will cause the ecu to run a bit leaner. (thinks its boosting less than it actually is)

Mrchips

iTrader: (7)

I wouldn't put one in, have you tried cleaning the pipes from boost solinoid to turbo.

-ant-

there all new pipes when i put the mbc on but its the exhaust thats made it do it more than it should. i want to get a dffrent one and sports cat but im skint till feb.

silent running

I'd never use one on any car. Not even on my old 200SX that cost me £600. I used a dawes device to whack the boost up a little and left it at that. The ECU fuels for it and the job's done. Once you start trying to trick the ECU beyond its limits then you end up with broken engines. There's a reason why the ECU has a fuel cut, just like there's a reason why it has a rev limiter - it's as far as you can safely go.

ALi-B

iTrader: (1)

On a classic scoob, all the FCD does is make the car think its running lower boost. This however does not affect fuel or ignition timing in any way, with the exception to the actual fuel cut failsafe itself.

The ECU handles boost separately to ignition and fueling. The MAP (pressure sensor) is used in the main to ensure the engine reaches its target boost and cut fueling completely should the boost limit be exceeded. Otherwise fueling and ignition remain pretty much unaffected. As these are handled by the MAF (airflow), oxygen sensor (for idle/cruise, not full throttle/boost) and knock sensor.

What does happen when using a FCD to allow high boost is that the fueling will respond more or less in proportion to the airflow. So more airflow, more fuel.

HOWEVER, under high load conditions (full throttle/full boost/high rpm) the ECU has mapped extra enrichment. Enrichment being making the car run richer than the technical ideal air fuel ratio. This enrichment is to provide quench effect and keep combustion temps at safe levels. The issue here is this is fixed by the ECUs programming, and running higher boost requires MORE quenching and thus more enrichment. The ECU will not compensate for this without reprogramming.

So what happen is that when running higher boost your eating into the safety margin provided by the enrichment; You can only raise peak boost levels by a finite amount until a point is reached where the car needs extra enrichment to keep combustion temperatures under control so that you don't go and melt some pistons.

Ignition timing is along the same lines; the knock sensor can only retard ignition within its set limits.

So, point being; the FCD itself won't kill the engine. But using it to allow higher boost without sorting the fueling and ignition maps will. As the engine no longer has a fail-safe system to prevent excess boost, and the ECU can only compensate by a limited amount - it cannot provide further enrichment nor extra timing retard that maybe needed in certain circumstances. Unless its reprogrammed, of course.

To iterate; using a FCD on a car running stock boost won't do anything. But using it with a boost controller be it electronic or a dawes has the potential cause harm to the engine. As will fitting a FCD to a car with stock ECU boost control, but is suffering from spiking/surging/overboost issues - using a FCD is not fixing the problem, which lies in the boost control (such as a undersized restrictor (MY97 onwards), blocked/kinked pipe work, purge solonoid issue or a tired wastegate actuator).

So the words "use with utmost caution" apply here.