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Old 01-23-2011, 06:37 PM   #51
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Re: VTEC-E question, help!

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Originally Posted by benfrogg View Post
I agree with you about throttle position for most every vehicle on the road. However, with this VX, even minute changes in throttle opening mean large changes in instant mpg. For example, most small hills I can climb in fifth gear. At half throttle (or a little under, I can maintain lean burn) and my mpg display goes down as low as 45mpg. As soon as I lose lean burn, it drops to 24mpg or so. That's at just over half throttle. 3/4 throttle is about 14mpg, WOT is single digits. Like 6-7mpg. So, yes, in theory more throttle will lower pumping losses, but the VX seems to be very sensitive to throttle position care of the TPS.
The problem with WOT on cars that aren't throttle by wire is that when you hit WOT, you actually go into open loop mode which means the car uses pre-configured fuel tables which are always more rich in order to "protect" the engine. "flooring" it on a DBW (Drive by Wire) car such as my Volvo S60 does not put the car into open loop, once the car is warmed up, it always is in closed loop mode. On my '98 Civic, I believe the car goes into open loop at about 3/4 throttle so it's pretty similar to your situation and what you've been seeing.
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Old 01-23-2011, 07:47 PM   #52
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Re: VTEC-E question, help!

Close but no cigar. It's not DBW that makes WOT happen without open loop, it's wideband O2. WOT doesn't even require open loop, but common programming assumes (quite correctly) that when most people floor the pedal they want maximum power at the expense of fuel economy. It could be programmed out if you don't mind sacrificing a few HP.

However, with DBW you will often get WOT even though you haven't floored the accelerator pedal. That WOT does NOT include open loop even if you don't have a wideband O2...but flooring it will still put you in open loop unless wideband-equipped.
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Old 01-23-2011, 11:35 PM   #53
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Re: VTEC-E question, help!

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Close but no cigar. It's not DBW that makes WOT happen without open loop, it's wideband O2. WOT doesn't even require open loop, but common programming assumes (quite correctly) that when most people floor the pedal they want maximum power at the expense of fuel economy. It could be programmed out if you don't mind sacrificing a few HP.

However, with DBW you will often get WOT even though you haven't floored the accelerator pedal. That WOT does NOT include open loop even if you don't have a wideband O2...but flooring it will still put you in open loop unless wideband-equipped.
Uh, do you understand that Open loop=not using O2 sensor but pre-programmed values? Having a narrow band or Wideband o2 sensor is irrelevant as to whether or not you're in open or closed loop when WOT. I just noticed that DBW cars don't go into open loop when they're floored because they can autonomously control the throttle valve regardless of pedal position. Something about being WOT on non DBW cars forces them to be in open loop mode instead. Keep in mind that even today, most cars use narrow band o2 sensors.
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Old 01-24-2011, 05:59 AM   #54
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Re: VTEC-E question, help!

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Open loop=not using O2 sensor but pre-programmed values?
That's exactly the reason why the type of O2 sensor in use determines whether you need open loop or not. A wideband O2 can provide the data necessary to make the maximum amount of power at WOT. A narrowband O2 doesn't provide the right data so it has to be ignored; it's basically a go/no-go sensor, while a wideband can say exactly how rich or lean it is.

Wideband O2 sensors are much more common now than they used to be. The correlation you've noticed with closed loop WOT and DBW is probably just because DBW also became common.

Your 2004 Volvo S60 Turbo's upstream O2 sensor is wideband, according to Oreilly Auto Parts:
http://www.oreillyauto.com/site/c/de...2205&ppt=C0018
My 2008 VW Rabbit was also equipped with wideband O2 and DBW throttle.

Can you suggest why DBW vs. cable throttle would make a difference?
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