Does anyone know what the pcm inputs are for a 93 lt1 to go from open loop to closed loop?

I thought it was just coolant temp, but it seems there must be something else.

(i suspect digital oil temp, bc my car wont go into closed loop, and datalog shows digital oil temp pegged low).

 

It's coolant temp activated. And the rest of the sensors must complete the loop.

 

Time, temperature and O2 switching.

 

No oil temp involved.

 

The coolant has to be above the threshold value for a certain length of time before it will switch to closed loop. The ECM keeps track of the startup temperature so it know how long to wait.

The ECM also looks for the O2 sensor to be hot enough to put out an accurate signal.

 

Sounds like a problem with the sensor on the water pump.

 

CTS coolant temp switch <> your talking about

 

I didn't answer because I hadn't looked at any 93 BIN's. Are you quoting that year,,,or your year?

It is true on my 89 that a minimum temp is required for closed loop. I suspect it's the best way to insure the O2 has heated up enough.

 

The year doesn't matter. The various versions of the ECM firmware have different values (very minor differences) for the parameters, but the basic operation is the same.

After the coolant temperature threshold is passed, the ECM starts looking at the voltage coming out of the O2 sensor. It starts out very low when the sensor is cold and finally passes the threshold value when it heats up. That's when the ECM goes into closed loop mode.

That's also why a non-heated O2 sensor in long tube headers will never go into closed loop mode. It just doesn't get hot enough to reach the threshold value.

 

The O2 sensor has a static ,power on (cold ) output of approx .45V

When the O2 gets hot enough ( >600F) to operate it, rapidily cycles lo - hi -lo ( 0.2V - 0.9 V) ;
It is that changing Voltage the ECM looks for to confirm O2 sensor is operational so it can go CL

 

Seemed logical to conclude that from the 85-89 bins I've looked at. Is the same true for ODBII bins?

In the ones I've looked at, there are 3 time values to wait for closed loop. The assumption (I made) is you couldn't drive that amount of time (from those temperature points) w/o the engine getting hot. The times are parameters so you COULD try and force the engine into closed loop before it's actually hot. (In fact, I shortened those times a bit on my faster-heating 383.) OTOH, I didn't find a reference to the ECM looking for valid voltage coming out of the O2 sensor. I thought cars with problematic O2 sensor temps gave erroneous O2 feedback versus not going into closed loop.

That's one of the reasons I was hopeful about the success of the VetteTech longtube headers. With their tri-y design, the builder had (and chose to take) the option of placing the O2 sensor in the first pipe junction. As such, it sits just as close to the manifold as stock. Probably a hair closer. So, my VT longtubes actually work just as well as stock (in terms of O2 operation). And, I don't have a heated O2.

 

Well... NO. When the O2 sensor is cold it puts out a very small voltage. As it heats up the voltage gradually rises. Keep in mind that you're running in Open Loop at startup, which is calibrated to run rich, which means a (relatively) high voltage from the O2 sensor. That means that the O2 sensor is headed toward it's "rich" output of about 800 mV. When it rises above about (depends on which firmware you're running) 550 mV the ECM switches to Closed Loop.

The "rapid cycling" is caused by the ECM, NOT the O2 sensor. The ECM cycles back and forth between rich and lean and the O2 sensor follows that rich/lean condition. This is CLOSED LOOP: the ECM commands a rich condition (wider injector pulses), the O2 sensor voltage goes up in response to the rich condition. The ECM sees the higher O2 sensor voltage and commands a lean condition, the O2 sensor voltage goes down because of the lean condition. This rich/lean cycling happens about once per second. Here's a scope trace from my O2 sensor at idle:



The .450 volt number is the Lambda 1.0 voltage, which means perfect combustion. The curve in the following pic is for 14.7:1 air/fuel ratio. If you're running gasoline with ethanol or other additives, perfect combustion is still Lambda 1.0 at .450 volts output but the AFR will be different. This is the response curve for an oxygen sensor:

 

I beg to differ .
A DM log from one of my '730 setups.
Cold start KOEO clearly shows .450V (Black line is O2 V output . Blue is rising coolant temp )