jmrussell89

Evening folks,

I’ve been really scratching my head about this lately. I installed a Driven Fab baffled catch can the other day and ever since my afr has plunged. Maybe it was doing this before hand, but I’m doubting it.

The weird part about it all? It’s Speed Density tuned, the car does not misfire, the spark plugs look fine, there are no boost leaks, makes the normal pops and bangs a side exit exhaust would make, and the sensors have been recently replaced. Why in the hell am I still seeing this? Is it fuel pressure? Bad regulator, etc.

I’m seriously lost. Car runs amazing, holds 28psi beautifully, and doesn’t even smell like fuel. I checked everything in my maps, logs etc and was all fine.

staywide8

iTrader: (1)

I had a similiar issue, but mine was lean. New wideband sensor fixed it. That would be my guess

jmrussell89

Sadly that’s not the case. The thing is, it reads the correct numbers at idle and cruising. (Should have mentioned that) and I’ve replaced the sensor recently.

staywide8

iTrader: (1)

Mine went lean anytime throttle was introduced, but read correctly at idle. Backwards, but still, the sensor fixed it.

jmrussell89

I guess I can give it a go and replace yet another sensor lol. I did save myself some money and bought the normal Bosch WB rather than the ridiculously marked up from AEM, but I don’t think that’d be an issue.

six40

No issue there, I've done it as well. Bosch 17018 is the correct replacement for the older AEM wideband sensors. The wideband o2 is actually used on the 2000-2002 Subaru 2.5 SOHC engine in various models.

jmrussell89

Yep, that’s the one I replaced with as well. It just seems odd that I’d get the same thing from two sensors. One three years old and one brand new. The new one got to 10.5 once before it just went back to showing 10.0.
I may see if someone in my town has one that I can plug in but I doubt I get different results. Sadly tuning is an all day affair, and a long way away, but if it just keeps doing it I may see if it really is a tuning issue. What effect a proper catch can would have is beyond me, but who knows.

six40

What you can do is reverse the catch can and go back to the way it was before, and see if your AFR's change. Short of that I'm not sure what it can be, as a catch can shouldn't change that especially on SD. AFR's in the 9's @ WOT are possible. You can have rich knock, but you can also have the car running fine depending on the tune. It is still unnecessarily rich though.

jmrussell89

Evoscan logs showed no knock, outside of the occasional 1-2 count in random places on different logs, and sadly the gauge only reads 10 so I can’t see what it’s actually seeing. I got in touch with my tuner if they could send a more in depth log file but they’ve yet to respond sadly.

The exhaust is pretty black, but that was pretty common even before it started showing this 10.0. I wanted to actually plug it back in normally, but crushed the front bung when installing the AN fittings. (Powder coating issue from a while back). With SD to run this way, there’d have to be some leak past the plenum, and if that was the case I would have noticed by now and the car wouldn’t run as well as it does, obviously.

I’ll eventually take it back to tune one of these days, as I’m worried this is false and am afraid of pulling fuel myself, when it doesn’t need to be. It was tuned using a WB in the tail pipe, so maybe it’ll show something different.