Wondering if anyone can help,
about a week ago I noticed my AFR gauge drop from rich to below lean as soon as I made any boost, 02 readings on PFC Controller also agreed giving 0.0v, this was after driving a little bit hard, then readings never went any higher that 0.2v but mostly 0.0v, so I replaced 02 sensor, and all seemed fine, although I never drove it on boost till yestarday, at slow speeds and idle 02 readings were flutuating between lean and rich"fine", but when I run it up on boost the reading goes to rich for a second then drops down to 0.0v again and dosent go back up to rich until the throttle is just slightly pressed"slow speeds", some times just stays at 0.0v till restated from cold.

I replaced the MAFS today " no change", also checked for leaks both vacum and boost both seem fine, hell the car still runs as sweet as ever "altough only running standard boost until fixed", but there must be something wrong, has anyone else experianced this problem?

I searched forum first and found problems with FSE FPR, could this be a possable factor?

It is a V2 WRX STI

Many thanks in advance

 

could it not be the wide band lambda has failed?

 

Don't have one present, readings are from the stock 02 sensor in manifold, checked it again this morning, readings are fine till I go over 3200 rpm! Then drops down to 0.0v "lean" but seems to run fine? Thanks

 

in that case the stock sensor must be wideband (though I didnt think they were):
a narrow band is simply a switch (more or less) and yo cannot get an accurate variable AFR ratio off it
a wideband gives a scaled output according to the AFR and is what you need to run a gauge
...I still think its your Lambda thats dodgy, imho

 

Thanks scoobian, replaced lambda 3 days ago and no change to readings, I know it's not as good as a wideband but I do know previous to this fault developing, the readings at the ecu for the 02 were about 0.8ish (rich) on boost but now it's dropping down as far as 0.0v (super lean) on boost,
I'm thinking of checking fuel reg, it's got an old fse, does anyone know the best way to check operation without replacing?
Thanks again

 

I would tend to agree

 

have you possibly just replaced a wideband with a "normal" narrowband Lambda & the PFR is no longer working ? ( a wideband is required )

just a guess.....

 

No I have used the same lambda part Number that I used when I changed it last(about 4 years ago),
got to the bottom of 1 problem today though, Checked fuel pressure and it was same as when I last checked it about 38psi "on idle", But if I blipped the throttle it shot up to about 75-80psi, never actually checked that before, but fitted a new Regulator set it also to 38psi on idle, and it only made about 50-55psi with a blip of the throttle, road tested, afr readings are still not right, but a wee bit better is it possable the car was over fueling soaking the lambda to mess up readings? or would it pick up on it running rich? could my new sensor possibly be nackered from this giving the wrong readings now, or do you think my problem is not related to this fuel reguator probem?

 

A normal subaru lambda sensor wont be any use at all for gauging your fuelling under full load conditions.
an AFR gauge connected to this narrow band sensor is also of no use.

Get someone with a wideband sensor and have it checked properly.
I wouldn't go down other routes just yet until you confirm what the fuelling is ACTUALLY doing.

 

bump

 

There could be a chance that your fuel pump is not flowing enough fuel to handle the requirements when on boost. Fuel pressure will look ok at idle and when blipping the throttle, but when you put some load on it, it won't be able to supply enough fuel to the injectors.

I had a similar problem when the intank hose from the fuel pump to the fuel pump assembly had a small split. A real nightmare to diagnose!!

A quick method to check fuel pump flow is to have your fuel return line pouring into a container. You should not see any appreciable difference in quantity when you blip the throttle.

 

narrowband ambda sensors do not usually control fuelling on boost.