I think I have the heated O2 sensor tuned in for the 7747 I have. By "think" I mean it doesn't surge anymore when I let it sit and warm up.

I think the sensor is lazy. No matter how long I sit, it never goes into closed loop. Should it? The O2 voltage is right around .893 mV if I just sit. The coolant temp has past the threshold, the timers have expired, but the O2 voltage WILL NOT swing until I start driving. A second or two after I start moving it will swing around then go into closed loop.

Whatcha think??

TIA

 

Often you MUST start driving for the ECM to go into closed loop. In fact, pro-longed idling oftens throws the ECM into open loop (a common reason people fail emission testing if they wait too long).

 

Ok. I don't really know what's "normal" O2 sensor behavior is and what isn't. This is the first time I've had to mess with it.


Often you MUST start driving...

Is that something that is programmed into the ECM, or is that "just the way it works"?

 

It's in the ecm. There are certain MAP high and low values to keep the car in learn mode. There are also hi and low o2 values to go into closed loop and to stay in closed loop.
My eprom has min MAP set at 17kpa and max at 102kpa. The o2 values to go into closed loop are: 556mv/243mv and the values to stay in closed loop are: 812mv/365mv.
Does anybody know if this is what make the ecm go into open loop at idle? What is the advantage of going into open loop at idle especialy now that he's got a heated o2 sensor?

 

Oh yeah I've seen something like that in some of the hacks I have. I'll have to dig out the hacks I have and add them to my WinBin ECU file.

I've often wondered why you'd want the ECM to go into open loop at idle. Doesn't the 454 bin do that?...I thought I heard that somewhere.

 

This seems to be a common approach that GM took with the various ECMs I've played with. My 7730 does this and my buddy's 165 running the $6E does the same thing.

In fact, not only does prolonged idle cause it to go into "open loop" but I have found prolonged deceleration down a long grade will also cause my 7730 to drop into "open loop".

As for the specific reason as to why GM did such a thing, I can only offer a couple theories...but I don't know the actual reason for GM taking this approach. Possibly Bruce does.

I figure it has either something to do with "fuel economy" (cause I always noticed that when my ECM goes into open loop on prolonged idle that the AF ratio is forced to 15.2; the O2 sensor becomes inaccurate, and forcing it to an AF Ratio produces less emisions; or it has something to do with protecting the cats.

 

I'm pretty sure that a lot of the 7747 bins had an open-loop idle from what I've heard/read. I've seen an aftermarket TTA chip that forced the idle into open loop any time the VSS was at 0 mph. I know you can program it to be that way too, as a few 4th-gen guys I know with big cams are going with a "PE idle" to keep things stable. My HOT-cammed 355 always stays in closed loop at idle with heated O2 sensor, and even before with the regular 1-wire O2 sensor, although my headers are Jet-Hot coated if that helps any. The open loop you're seeing Glenn is possibly from DFCO or decel enleanment.