is it normal to go open loop when decel?

[Laminar Lou]

I've got this nifty scangauage and have been playing around with it.

One thing I have noticed is that the Tundra goes into open loop when letting off the gas at freeway speeds. I understand why it goes into open loop at WOT, but what is the reason for it to do it when it is decelerating in a modern fuel injected engine?

 

[Master ACiD]

i dont know but the last 2 cars i owned cut the injectors off under deceleration like that.

 

[Mokanic]

What type of nifty scan gauge?

 

[moribundman]

My Audi injects a shot of fuel right after I get off the gas, resulting in nifty exhaust burbling when unburnt excess fuel hits the two cats. My A/F meter confirms this burst of fuel.

 

[Laminar Lou]

Hmm... maybe I need to do some reading. I thought this would have been one of those easy questions.


Mokanic,

Google "Scangauge II". I'd post a link but they aren't a sponsor and I don't want to violate any board rules. It's a pretty neat gizmo.

Admins,

I tried to edit my post but the time limit has expired. I want to get rid of that smiley of a thinking person because, well, you can see what the source server replaced it with.

 

[brianl703]

Open-loop simply means that the ECU is not using the input from the O2 sensors to control the air-fuel ratio.

Since the ECU is almost certainly turning off the fuel during deceleration, there is no need for it to use the input from the O2 sensors, therefore, open-loop.

 

[Gary Allan]

It's what my Jeep FSM states as normal under hard deceleration. It takes in all kinds of data (VSS, coolant temp, battery voltage, AC select and request status, MATS, MAPS, cam & crank sensors). It then, as brian says, ignores the O2 sensor and cuts the ground to the injectors (termed a fuel cutoff strategy). If it's not perceived as hard deceleration, then it chooses the proper pulse width for continuous fuel injection. The PCM then, via the AIC, sets the idle speed.

Although it doesn't say that it ignores the O2 during non-hard deceleration, it doesn't assert that it does

It's still considered an Open Loop operation ...or at least the second sentence indicates so without qualification.

 

[Laminar Lou]

Brian,

Thanks. I did a little searching and found additional evidence to support it was normal.

 

[MC5W20]

yep, according to my OEM produced service manual for my car. When you let off the gas at speed, the ECM will stop the fuel injectors. This is a fuel saving strategy. It will only turn the fuel injectors back on if gas pedal is pressed or speed drops below the threshold that would stall the engine.

 

[brianl703]

It's also an emissions control strategy--according to one book I've read, the biggest emissions control problems with carb'd vehicles are at decel. With FI, they can just turn the injectors off to solve that problem.

On my 2006 Saab 93 it is pretty noticeable when the injectors are turned back on when decelerating (it is a stickshift). They are turned back on right around 1000RPM.

On the Ford vehicles I've driven that are stickshift it's not so noticeable. Maybe Saab could check with Ford for some better decel strategy code

Actually come to think of it Saab's way might be better. You'll certainly never forget you left it in gear and stall the engine when coming to a stop!

 

[mechtech2]

The fuel is cut off under certain de acceleration parameters.
It's a good thing, and save fuel and wear from fuel wash.