Air Fuel Gauges & stock ECU question

[Lude]

basically my car does like to over boost (over 1.3 kg/cm2) and im scared of running lean.

 

so i dont floor it past that (need to play about with my restrictor ring in exhaust)

 

 

1) what boost is the stock ECU capabale of fueling? without running lean/detting?

 

2) where does the aftermarket AFR gauge (wideband) plug into, if the stock lambda is in exhaust?

 

3) will the aftermarket AFR gauge tell me if my stock lamda sensor needs replacing? (obv if running rich im using more petrol than needed)

 

 

my car is fitted with an Apexi SAFC, but im not sure how its setup, and it doesnt fill me with confidence tbh (hence reason for quetion 1)

 

 

help would be apreciated, love to learn & understand bit more advance.

PS car is J specTT6 BPU, (Blitz FCD, exhaust n filter, FMIC, double decat)

Edited January 9, 2011 by Lude (see edit history)

[Homer]

1) The stock ECU is only "mapped" to 1 bar IIRC, therefore as soon as you go past this you're relying on the overhead to keep the fueling in check. They are mapped to run very rich as stock (which is one reason why decatting and raising the boost pressure has such a dramatic effect on performance).

 

However, the stock injectors and map will supply enough fuel to keep safe AFR levels at higher RPM's, it's actually the transition point and in particular when the 2nd turbo first reaches full boost that the map will cause a slight lean condition, usually 3.8k to 4.4k rpm. This is the point that needs to be kept an eye on, I've seen many supra's getting into the 13+afr range here.

 

Your SAFC may well be doing more harm that good though, especially if you don't know what it's been setup for. THe SAFC is too crude a device to effectively map out the transition point lean condition but can help. However it won;t make any difference above 1.0bar since the injectors will already be 100%, I.e. it can't add any more fuel than is already being supplied.

 

2) The AFR wideband sensor is normally mounted 18inches or further from the turbo, however most 2nd decat pipes will come with a boss welded on for the WB sensor to plug into. This is normally just under where the gearstick is so make it easy to feed the sensor line into the passenger cabin.

 

3) The AFR gauge will give you an idea if you are getting lean AFR's and should be essential when doing BPU mods. It's more there to help you know if the car is developing a problem and working well rather than a gauge you check when daily dirving. People call them worry gauges for good reason

It won't help you save your engine and if you do see a seriously lean condition as the detonation will already have occured by the time you react to it.

 

Personally I'd want to look into the cause of the overboost, however the addition of an AFR gauge should be no1 on your list.

[Lude]

thanks mate, so the SAFC is only helping up until 1bar of boost then no good?

 

if the ECU + injectors can only produce a safe amount of fuel for 1bar boost, why do so many run stock twins on 1.2? must not be aware of it? or is some lean fuel ok, just as long as not a dramaticly lean amount.

 

im guna get a smaller restrictor ring & AFR gauge then, hope 1.2 + 1.3 hasnt done damage to my 2JZ

[Homer]

At 1bar it is still running pretty rich so it's "safe" to run at 1.2 bar as there's enough extra fuel to avoid detination. As always, it is a bit of a risk as any fueling component that's not running 100% can easily reduce fuel supply and result in det. This is why the BPU mods include items like new fuel filter and pump & an AFR gauge to keep a check on things.