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part throttle boosting

Old 02-24-2004, 12:42 AM
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Default part throttle boosting

So, with the hack, or a chip, you change the fuel settings. BUT, those settings only really take effect when the car is running in open-loop mode, right? Then it is using the map. Otherwise, it is constantly adjusting based on the o2 reading to keep itself at or near stoich. So, my question is, what prevents us from blowing up our motors at 10 psi and 75% throttle when we are running an afr of 14:1 - because it is running closed-loop using the o2? Is this one reason I hear you aren't supposed to boost in 5th?

IF (a big IF :P) I'm on the right track, wouldn't it be better to "hack" the o2 (send the ecu a lower voltage) so that it thinks it is at 14:1, when it is really 12:1, or something like that? It doesn't sound impossible, or even terribly difficult to me, and I know virtually nothing about building electronics. Has anyone tried this? Would it work? Would it be possible to fool a chipped computer using a software fix instead?

Or am I on the wrong track entirely?
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Old 02-24-2004, 09:37 AM
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Default Re:part throttle boosting

Hmm... dunno exactly.. BUT.. from what I've noticed so far when going into boost at part throttle A/F meter show I'm going more and more into rich area (this is for about 50% throttle), and LEDS don't buce so much up'n'down.. but stays whole time in rich part.
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Old 02-24-2004, 11:05 AM
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Default Re:part throttle boosting

The A/F meter physically is set to stoik. If youve seen the graphs its ~0 volts when rich and ~5V when lean, and right at stoik its a very sharp jump so there would be no way to scale this to lets say 12.3:1 as an ideal instead of 14:1. This is the whole idea behind the WIDE BAND is that the voltage is proportionate to the A/F not just like an on off swith that either tells the computer that your either lean or rich.
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Old 02-24-2004, 12:42 PM
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Default Re:part throttle boosting

Originally Posted by d16tuner
So, with the hack, or a chip, you change the fuel settings. BUT, those settings only really take effect when the car is running in open-loop mode, right?
Nope. It's using the fuel and ignition maps as a reference during it's closed loop routines. It's just also factoring in the O2 sensor voltage, TPS, ECT and IAT as well..

So, my question is, what prevents us from blowing up our motors at 10 psi and 75% throttle when we are running an afr of 14:1 - because it is running closed-loop using the o2?
Tuning of the rest of the map. If the maps were strictly used at WOT (+80% TPS by the ECU) you would only use the right most columns of your maps. (the "high pressure" zones). the lower parts of the vacuum 26inHg to 4inHg are used for part throttle.

Is this one reason I hear you aren't supposed to boost in 5th?
Boosting in 5th is fun. ..but, sort of. If you can't tune your maps, don't boost in 5th. Simply because if you look at a Map Trace of 5th gear driving your RPMs are so low, you'll be at a low fuel point on the map (mid right portion). Normally on a hack, this isn't enough fuel to adequtely cover full boost. But, if you can tune it, drive it, who cares..

IF (a big IF :P) I'm on the right track, wouldn't it be better to "hack" the o2 (send the ecu a lower voltage) so that it thinks it is at 14:1, when it is really 12:1, or something like that?
I couldn't see how one would accurately be able to gauge the fuel compensation by the ECU if one were to scale O2 voltage, simply because the single wire O2 voltage scale is not linear. It's about .92v at 14.2:1, and .05v at 15.2:1. Otherwise, the curve is non existant, and it's flat lined.Your O2 can't see anything outside of that range.
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Old 02-24-2004, 01:00 PM
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Default Re:part throttle boosting

wouldnt tuning *with a wideband* be better in 4th and 5th gears then? sence your are moving threw the rpms a little slower....whens some good datalogging ---- gonna be finished
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Old 02-24-2004, 05:05 PM
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Default Re:part throttle boosting

Originally Posted by d16tuner

IF (a big IF :P) I'm on the right track, wouldn't it be better to "hack" the o2 (send the ecu a lower voltage) so that it thinks it is at 14:1, when it is really 12:1, or something like that? It doesn't sound impossible, or even terribly difficult to me, and I know virtually nothing about building electronics. Has anyone tried this? Would it work? Would it be possible to fool a chipped computer using a software fix instead?

Or am I on the wrong track entirely?
As others have pointed out, the stock O2 sensor is essentially a switch and has no linearity. It's just either "rich" or "lean." The ECU changes from rich to lean which causes it to cycle on an A/F gauge. It's this toggling of the cycle that averages out to a 14.7:1 AFR.

As TurboEF9 so excellently pointed out, the O2 sensor's signal is just a correction to the already existant fuel maps.

-Tim
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Old 02-24-2004, 09:56 PM
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Default Re:part throttle boosting

Originally Posted by TurboEF9

Nope. It's using the fuel and ignition maps as a reference during it's closed loop routines. It's just also factoring in the O2 sensor voltage, TPS, ECT and IAT as well..

So, my question is, what prevents us from blowing up our motors at 10 psi and 75% throttle when we are running an afr of 14:1 - because it is running closed-loop using the o2?
Tuning of the rest of the map. If the maps were strictly used at WOT (+80% TPS by the ECU) you would only use the right most columns of your maps. (the "high pressure" zones). the lower parts of the vacuum 26inHg to 4inHg are used for part throttle.
DUH I really should have thought of that. you'll neever be at -25.54 in/hg at WOT unless something is broken. lol. So, yeah, that makes no sense. I'm glad because it was really starting to worry me. I couldn't figure out how my engine could run 14:1 and not blow under boost. Should have known if everyone else is doing it there has to be something else to it. Oh well, thanks for straightening that out for me. And yeah, I knew the o2 offers poor resolution at a low ratio like 12:1, but based on my then understanding of closed-loop vs open loop, I couldn't see any other way.
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Old 02-24-2004, 09:59 PM
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Default Re:part throttle boosting

That was actually a good question. Nice to see people getting interested in tuning their own setups and learning how it works
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Old 02-26-2004, 02:27 AM
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Default Re:part throttle boosting

Originally Posted by TurboEF9

[b]Boosting in 5th is fun.
thats all i understood from this post :P
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