I was just thinking about this the other day when I had a post about WOT AFRs.
I thought that the ecm went into open loop because it goes right to 128 BLM when you smash the pedal. If it goes to 128 directly than what good is the o2 sensor? Does the integrator still move around under PE mode?
Please help me understand this because I'm about to hit my head really hard against my keyboard (quiz today and bad head cold).

------------------
, Jon (350 TBI!)
91 Red My website

 

The O2 is only used in closed loop. It is what closes the loop, meaning the ecm is not only figuring what it thinks things are but it has FEEDBACK, this feedback to what it is doing is being closed loop.

WOT/PE, is a special condition, it just ignores the O2 and goes to a set of defined AFRs. Another special condition is accleration enrichment.
Most scanners just display an *inidicated* closed loop, since it's in closed loop, and is just a special condition. Different programs/ecms will vary on how the scanner sees things.

When in full closed loop, the ecm does not try to maintain a 14.7:1 AFR. It deliberately toggles across that point to keep the converter working, and min emissions. So it AVERAGES a 14.7. That's why the swings across Stoi., vary so much.

Also, some programs go to a rich BL correction if present, meaning some ecms read 128, and some might read say 135 at WOT.

 

Okay so how does the ecm know that it's giving a richer AFR under WOT? How the heck does it know without using the o2 sensor for feedback? Am I right that the ecm goes into open loop under WOT?

------------------
, Jon (350 TBI!)
91 Red My website

 

Closed/open loop has nothing to do with WOT conditions. Closed loop occurs mostly when the coolant temp is warm enough, and maybe after some engine run-time timers engage.

When you nail the throttle, and hit the PE mode, "learn control" goes off, thus the ECM ignores the O2 sensor. In this mode, the ECM uses other tables/parameters to control fuel. Since you are adding more fuel, richer, the AFR is lower than normal. You should also observe that the O2 sensor should be steady at a high level, around 900mv. That is also the indicator of WOT. The actual level kind of depends on the state of the sensor.

Hope this helps.

------------------
Best ET 14.413 @95.57 without
pulling valve covers or manifolds.
Also with stock 2.77 rear end!!!

 

Yea go tell that to car craft. in their issue this month they said they were going to turn up their fuel pressure in their bird for better atomization and that it wouldn't change the mixture because the o2 sensor would correct it. LOL

 

The ecm doesn't know or care what the O2 voltage is at WOT.
Like I said WOT, and AE are special conditions, where the O2 is ignored, thou in some calibrations a corrected BL is used.

 

well they got it 1/2 right, as far as trying to correct idle/cruise.
Amazing they get anything right any more.
The magazines are really getting funny, all they want are english majors, it's more just repeating what their adverizers tell them is the truth.

 

So learn control goes off but closed loop is still on, right? Okay, if that's the case then that would explain why the ecm would go into a different BLM because of MAP voltage.
Why is it that at idle that some cars (if not all) go into open loop. Is it because of the low map reading or what?
Grumpy, can you please e-mail me, I'm in Ohio now and I'd like to talk to you about a few things.

------------------
, Jon (350 TBI!)
91 Red My website

 

Not all calibrations allow for open loop idle. And the reasons for doing that vary.
Overheating converters, being one.

 

Once you get into closed loop, you usually stay there unless the car cools down. If you are idling for long period of time, the O2 sensor may cool down enough to not function. Remember the sensor has to heat up to around 600deg before it starts working. Thus the need for heated sensors. It also depends where in the exhaust flow the sensor is located. My '92 GMC S15 has a heated sensor, but my Camaro doesn't. The truck sensor is a little downstream compared to my IROC.

When idling for a long time, I don't think the ECM is the one who decides to go open loop. It is the O2 sensor, which stops working because of low temp, that forces open loop.

Grumpy correct me if I am wrong.

 

A *cold* can send an ecm into open loop. That can also set a code 13 in come calibrations. If you look thru the Mask ID 42 cals, there are some that have a timer, that sets the open loop idle, ie no VSS for x mins and it goes open loop at idle.

The manufactures play all kinds of *tricks*.
One of the big three had a tie in from the ecm to the door jam switch.
Why?.
In the EPA tests they chassis dyno'd the cars with the dr door open, so they had a lean cruise enable that in part was triggered by a door jam switch.

 

Grumpy, you know WAY too much, lol.

------------------
, Jon (350 TBI!)
91 Red My website