quicksilverado

iTrader: (8)

With the cut outs open the turbo will move more air. Unless you are SD tuned, the afr could get lean enough to loose an engine. The o2s will not compensate for the extra air.

Rick_Vor

iTrader: (36)

I could see that happening if you have a really restrictive exhaust and a small wastegate so you would get boost creep with it open. Otherwise, wouldn't the wastegate keep the same limit of boost regardless of the exhaust backpressure?

Rick

quicksilverado

iTrader: (8)

Not always. It can also happen when you remove the air filter, which some people do at the track.

slow67

iTrader: (2)

Also with full exhaust vs open cutout, less backpressure = more hp, which requires more fuel....and O2s don't compensate at WOT on factory PCMs.

chpspecial

iTrader: (1)

Actually the o2 sensors do correct fueling at WOT. they apply the same LTFT factor at WOT as they do in closed loop fueling. So while its barbaric, it still does provide some correction.

silver-mod-o

iTrader: (15)

That is true... Some fueling adjustments are done using long terms. But as stated it's barbaric at best.

I kind of always assume everyone running forced induction setups on these things is tuned open loop speed density. I know when I took the MAF and O2's out of the equation and started tuning only with a wideband, reading plugs, IATs etc, my fueling got more accurate and was far easier to control.

My opinion about the cutout thing is this... If you want it super quiet and run a fairly restrictive exhaust then yeah I can see having one, otherwise just run a free flowing exhaust system and let it be what it is...

Rick_Vor

iTrader: (36)

I see said the blind man as he picked up his hammer and nails...

Makes sense. The motor will see the same boost level but becomes more efficient hence it is moving more air at a given amount of boost and becomes lean.

Rick

AKlowriderZ71

iTrader: (22)

I don't believe this is true. The O2's are only used in closed loop, as far as I know. As soon as you go WOT, or even into PE, the PCM goes into open loop. This is when a failing MAF sensor will rear its ugly head.

I've ran across this 2 or 3 times. Step on the throttle, go into PE, watch the scanner show the switch from closed loop to open loop, then watch left & right fuel trims go way lean. As soon as you lift, goes back into closed loop, and no longer lean. When I see that, I install my "known good" test MAF, and go for another drive.

Just my own thoughts & experience on the subject, trying to help.

For the record, I also believe that any force induction setup should have a 2 or 3 bar MAP speed density OS, instead of just a MAF.

slow67

iTrader: (2)

X1000....O2s only react in closed loop. Yes it will remember LTFTs at WOT, but the only way to get any values is to be near that area (on the VE table) at part throttle. For this very reason, most tuners don't use LTFTs, they leave them disabled and use STFTs only.

silver-mod-o

iTrader: (15)

Yeah, I just did some reading to verify that.... I haven't looked at fuel trims in so long it's pathetic lol. Most everything I tune is OLSD anyway. Doesn't matter if it's n/a or f/i