ksg10

Been reading up on AFR gauges on here and one thing that keeps coming up is narrowband vs wideband. Can someone explain the difference to me, and is there any real benefit to choosing the more expensive ones as opposed to the £40 ProSport one off eBay?

bengo

iTrader: (17)

A narrowband sensor is not very accurate and will only show AFRs around stoich (14.7:1) which isn't very useful when your car is boosting (openloop). A wideband sensor can measure a much larger range of AFRs (usually between 9:1 - 20:1).

HTH

Ben

JTinnovations

iTrader: (2)

To add to that - a narrowband only reports "rich" or "lean"; it's a binary device essentially. The ecu changes fuelling so that the average of the readings is neither rich nor lean, which means stoichiometric (14.7 AFR with pump fuel or, more pedantically, a lambda of 1.0).

Bristol98

That would explain the constant bouncing of my needle then, unless on WOT, then it sticks to rich....

ianbott

I'm more confused than before now after reading the last couple of posts, lol.
Are they necessary? what could you do with the info from the afr?
Thanks Ian.
P.S sorry for the hijack.

bengo

iTrader: (17)

It's normal for the AFR to bounce around 14.7 when in closed loop, apparently Subaru added this to preserve the exhaust cats and for emmisions. My wideband hunts around 14:3-15:2 in closed loop.

JTinnovations

iTrader: (2)

I would say they are of dubious value on a stock tune - if the narrow band fails, you'll get a CEL and the ecu will fail-safe and make sure the fuelling is OK. Likewise, the stock tune is very safe and will err on the rich side on boost.

Once you start modifying and remapping, then the map is being taken away from it's completely-safe targets in order to get more power etc. This reduces the margins of error.

If your engine starts running lean on boost (which the standard narrow band cannot measure; and at which point the ecu is running from fuel tables without the benefit of a lambda to keep things adjusted) then, most likely, bye-bye engine.

So a wideband is definitely useful to keep an eye on things.

Are they essential? No, not really, but they can be useful. I ran my 360bhp '05 JDM STi without one for years...but I did kill it when I made an ill advised mod and ran lean *off boost* for 80 miles: a wideband might have caused me to pullover and have the car towed...I'll never know

I have a wideband now, but then I'm running a Syvecs in fully closed-loop mode - i.e. the fuelling on boost is also controlled by the lambda so the ecu targets very specific lambda values at ALL times. Nice

ianbott

That's a really good explanation, thanks

eelz

iTrader: (10)

Don't suppose you'd care to share with us 'that' particular mod please mate? just as a precaution for others.

JTinnovations

iTrader: (2)

I decided to fit an RCM intake trumpet with a 'kin large K&N filter. It had an 80mm MAF tube...and I knew I was not to fit until just prior to the map. I fitted it at home and drove the 80 miles to meet the mapper, thinking that counted as "just prior" whereas I not have fitted it until I was actually with the mapper

The car ran lean, ending up with cracks around the spark plugs (larger than the usual ones you get on scoob heads) and low compression on 2 cylinders

The good news was that it gave me the opportunity of having a forged 2.5l built, which now runs 525bhp and similar torque on 10% meth (see my TimH username on here for details )