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Engine Management, Fuel, Spark, EGTs, and Air/Fuel Ratios This forum includes general electrical, modification, tuning, repair, replacement, identification and restoration of all components mentioned above including SMEC, SBEC, Logic Modules, aftermarket engine management, etc. Nitrous oxide posts go in here. This is the place

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Old 04-01-2008, 04:00 PM   #1
When does the engine switch to open loop?  
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I know on my tbird it switches at 3000 rpms, causing a good 5 mpg drop at around 80 mph. Im just wondering if theres a similar thing on the shadow. Also wondering if theres a certain amount of throttle that triggers it, as well as boost pressure.

Im basically trying to figure out the most fuel efficient way to drive the car right now, and to accelerate in the engines efficiency range and avoid accelerating like grandma.
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Old 04-04-2008, 01:22 AM   #2
Re: When does the engine switch to open loop?  
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Nobody knows this stuff?
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Old 04-04-2008, 03:30 AM   #3
Re: When does the engine switch to open loop?  
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Nobody knows this stuff?
:)I don't!
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Old 04-04-2008, 04:08 AM   #4
Re: When does the engine switch to open loop?  
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sounds like an interesting thing to do, would like to get some info on that too! doesnt it just switch to open loop under WOT only?
anyway, is there any kind of easy ALDL/OBD stuff you can scan these cars with? I'm comparatively new to these TDs, but on the 3gen F-body you can just hook up a cable to your laptop and check if it's in open or not (sorry, dont beat me for the F )

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Old 04-04-2008, 06:00 AM   #5
Re: When does the engine switch to open loop?  
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When the car is in open loop, the car basically ignore o2 feed back and runs on it's default mode, things can that cause open loop is listed below, as far as I can find...

1. WOT the engine
2. Several limp mode
3. When the main monitor devices are up to temperature or ready (coolant temp, o2, map)...
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Old 04-04-2008, 06:08 AM   #6
Re: When does the engine switch to open loop?  
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that's exactely what i already knew from the chevy small-blocks.
but, as bhazard already stated, some may also open at a specific rpm, and on our vehicles, maybe on a specific boost rate?

edit:
isn't proper temperature like the cts and o2 actually CLOSING the loop?
till the o2 heats up to 600F it doesn't even give useable information imho!
normal operation = closed loop, right? so it's only opened when you just did a cold-start and monitor devices have to warm up to function properly
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Old 04-04-2008, 06:11 AM   #7
Re: When does the engine switch to open loop?  
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tryingbe is keeping our cars running
I think his mpg drop is cause by increased aerodynamics and drag.

There is no open loop by boost setting in the calibration, only open loop by WOT.

Download Dcal or MoparCHem and open some of the calibration and start looking.
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Old 04-04-2008, 10:11 AM   #8
Re: When does the engine switch to open loop?  
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I think tryingbe meant when the sensors AREN'T ready.

I guess it would make sense that it doesn't switch to open loop at a certain rpm, since I cruised to WV at about 3500 rpm and still got 30 mpg.

And judging by that I would say that you could accelerate at a brisk rate and not take a serious mpg hit.
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Old 04-04-2008, 08:19 PM   #9
Re: When does the engine switch to open loop?  
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Old 04-04-2008, 08:42 PM   #10
Re: When does the engine switch to open loop?  
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5-7psi also puts you into open loop. It's easy, get a cheap a/f gauge and you'll be able to tell when you're in closed or open loop. Our computers are much more sophistcated than the Ford crap of the same era. RPM's have no effect in what loop you're in.
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