Ok...so everything is quiet as a mouse until I get to 6000rpms in 2nd or 3rd gear (note: not 4th or 5th) whern the knocklink starts lighting up.....get big red at 6800rpms.

Also flashes Red when I lift off if it HAS been detting?

AFR is as Rich as Richard Branson.

Am only running 0.9Bar, so what could be causing this?

Poor spark?

Has only been a problem since H&S exhaust was fitted.

 

Could be that now exhaust is running so freely, there is limited back pressure in system, so may be the cause. This will also be one of the reasons for the A/F ratio so high, as due to higher gas flow out, the flow rate "in" also increases.
But, no doubts, as I've responded, someone else will come up with yet another theory!

 

Crapola batch of fuel if this is new.
Optimax has apparently taken a down turn recently if you use that, otherwise some prat could have simply stuck the wrong fuel from the delivery tanker in the wrong container (happens all to often, it seems...)

 

Don't think it's the fuel......appeared as soon as the exhaust was fitted, and at 0.9Bar car SHOULD still run fine on 95Ron.
Esp as AFR is so very rich, bad fuel would show lean AFRs.

Good suggestions, though.

Why would NO backpressure cause det on a TurboCharged car?

 

Erm, a few little things here...
No Impreza should be run on 95RON. They weren't designed or set up for it, even in the UK. The car can run on it - I suspect it could be run on supermarket 91RON too but like a bag of junk (which it may well become shortly after using it...).
In totally standard trim, the ECU can probably cope with the 95RON stuff. Make the exhaust more free-flowing and you will improve the VE of the engine, it'll require less advance (ie will need less advance!) and could easily move beyond the amount of retard the ECU is able to apply. In short, the engine is more efficient, will be more 'sparkly' and will need better fuel to cope without det.
And you can get det irrespective of how much fuel is lobbed in. The engine runs rich in order reduce cylinder temps - if the fuel is bad enough, however much cooling is applied the flame-front can still be too fast for the timing.

 

It's a Legacy, not an impreza, and the factory map definitely supports 95. It says so in the manual. It also say 98 is reccomended


So would reducing the VE of the engine fit with the "High RPM det" pattern that I am getting? It's only ever run on Optimax, so I am fairly sure the fuelling is okay. Indeed I had no choice but to resort to a £5 of 95 in there the other day, and the problem was no worse.

I wonder if the knocklink is picking up something else other than knock? Or is it that my VERY old sparkplugs and coilpacks are not combusting the fuel properly?

Have to comment that I can't "hear" any det, though at such high RPMs I dunno if I could anyway.

 

Ok, whichever - it's the same engine
And forget the manual - I think you'll find that was all changed by the marketing people. Have a look at an identical EU model & it has 'use no less than 98 RON' plastered all over the place.

Yup. well, 6k is getting to the point that there's noise all over the place anyway! 4,500rpm is the touchy bit (point of maximum VE) so I suppose the only way to check is with det cans - could be the new exhaust banging against something
But, with the combination of the currently iffy Optimax & a few drops of unleaded, it might be enough to throw it anyway.

 

not an expert but,

1. i think that the ecu sets itself up according to lowest octane of fuel it recieves and does not increase itself upon returning to higher octane (SUL). thus will not be running correctly.

2. after about 6k rpm with just an exhaust, i believe the torque curve starts to drop considerabley and to no real performance benfit.

all IMO

Weava

ps: i also have found that my wrx overfuels now with complete H&S system, due to lack of cats i am told.

i am sure there are plenty of views- i wait with interest



[Edited by mista weava - 9/9/2003 3:57:56 PM]

 

Dude, I think you'll find that's only the newer ones that adjust automatically. And they have limited scope for retarding the ignition as knock protection so I wouldn't rely on it, especially if it's an import. Nom, am fully agreed that changing the exhaust will change the VE of the engine, but even on a really bad batch of fuel it shouldn't result in det on a car that is running 0.8Bar of boost (peaking at 0.9) when the AFRs are rich.
As you say, I suspect it is a lot more likely that the knocklink is picking up 'background' noise, especially as it blips into the red after lifting off at high revs, when the engine SHOULD be over fuelling (VTA Dumpvalve).

Anyone else got any ideas? Would a bad spark cause Det? Could it be my knocklink is knackered (the red light comes on dimly for a few secs on power up, so it's possible).

As you say, I think I will be investing in a set of det cans shortly.