closed or open loop?

Is there a definitive way to tell if my '88 Renix is in closed loop?

I don't know if there a test you can do to determine if it's running closed or open? Are you having some symptoms?

YES! Absolutely, positively!

If you can rig up a backprobe or wire tap to the two smaller black wires (not the larger gauge orange wire) on the O2 sensor wires with the the O2 sensor still connected to the harness, then with engine runnning and using an analog volt meter you can watch it rapidly oscillate from lean to rich across the 2.5 volt threshold at idle. At idle it will oscillate from about 1 to 4 volts about once per second in the closed loop mode. At 2000 rpm or higher it closes the gap to a 2 volt to a 3 volt oscillation across the 2.5 volt target. Rapid decel will peg it rich for about 5 to 10 seconds (less than 1 volt as I recall) before it goes back to a 1 to 4 volt swing. If it is running open loop, and rich it will display anything for 0 to 1 volt at steady idle. More importantly it will not rapidly oscillate back and forth across the 2.5 volt mark in open loop.

If your O2 sensor's heater is working and getting 12 volts it will go into closed loop shortly after start up on the Renix.

This only applies to the 87 -90 Renix system.

The O2 voltage on the 91 and later models dropped to a 0 to 1 volt range with .45 volt target.

Dont quote me here but closed loop should be anytime the engine is warm enough to open the thermostat.

jeepfreak84 said:

Dont quote me here but closed loop should be anytime the engine is warm enough to open the thermostat.

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Thats when I can tell my Renix is in closed loop, it idles down a hundred or two RPM's after it warms up. Or in other words it idles up a little when it's in open loop. It idles up for the first 10-15 seconds after startup, then the idle comes down some, then down a little more after the thermostat starts working and the gage shows just over a quarter or so. My tach just isn't that accurate at lower RPM´s, I'm not going to even try and peg specific idle RPM's to open and closed loop. But a little higher and a little lower I can detect by ear and see by the *relative* position of the tach.
I've read that it goes closed loop at around 140 F. Though the 02 sensor seems to kick in earlier.
Maybe it's just the Renix I have now, the last one wasn't nearly as temperamental as this one (or maybe I just didn't notice the quirks as much).

Mine @ start-up mode 12-1500
Warm-up mode 1000
Idle mode 800
but that's mine

People get screwed up a bit with open and closed loop. If I can remember them all, it's startup (crank) open loop, warm up open loop, operating temp. idle closed loop, operating temp. cruise closed loop, deceleration closed loop and wide open throttle open loop. Various sensor inputs are used and ECU outputs change with each mode.

I've been thinking of running a very small indicator light to the EGR solenoid ground wire at the ECU (it switches at the ground). The EGR solenoid should not denergize unless the motor is in cruise closed loop mode. Or in other words when the indicator light goes out (battery power to the lamp, ground through the EGR ECU ground lead), you are in closed loop cruise. The EGR solenoid is default open, which means that to actuate it (turn on the vacuum) it has to be deenergized, or the ground interrupted. Won't help to tell if you are in closed loop idle or not, but something anyways.
I've also been thinking about doing the same (a small indicator light) to tell me when my torque converter is in lock up.

jeepfreak84 said:

Dont quote me here but closed loop should be anytime the engine is warm enough to open the thermostat.

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Not a problem, I won't quote you! :laugh3:

8mud,

I disagree with both of you on this one. I had my 87 Renix for 2 years before I had a working, installed attached O2 sensor on mine, and during those two years the start up idle was just as you two described. The Renix does not go into closed loop mode with out a working attached O2 sensor.

Now that I have everything working properly on mine, it starts up at 850 RPM, drops down to 750 RPM after a few seconds and stays right there, hot cold, warm, first days cold start up, or the last fully warmed up start up of the day. I have entirely eliminated the high idle even at start up now. In park it idles at about 575 RPM warmed up, 650 rpm cold. These are all according to my OEM tach.

Ecomike said:

Not a problem, I won't quote you!

8mud,

I disagree with both of you on this matter. I had my 87 Renix for 2 years before I had a working, installed attached O2 sensor on mine, and during those two years the start up idle was just as you two described. The Renix does not go into closed loop mode with out a working attached O2 sensor.

Now that I have everything working properly on mine, it starts up at 850 RPM, drops down to 750 RPM after a few seconds and stays right there, hot cold, warm, first days cold start up, or the last fully warmed up start up of the day. I have entirely eliminated the high idle even at start up now. In park it idles at about 575 RPM warmed up, 650 rpm cold. These are all according to my OEM tach.

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Renix's are like women, they all have the same basic equipment, but all have there individual quirks.
O2 sensor is used in every mode except crank, wide open throttle and under 1200 RPM decel(I think), but the book says you don't get a true closed loop until operating temperature. And even a closed loop, has different sensor inputs and ECU outputs depending on the mode.

Renix's are indeed like Women, they go through cash and credit cards like gas in a Hummer! :shiver:

I suspect what they mean by operating temperature is the operating temperature of the O2 sensor! In which case the HEGO-Renix sensor gets there in about 10 seconds or less because it has a built in sensor heater.

8Mud said:

Renix's are like women, they all have the same basic equipment, but all have there individual quirks.
O2 sensor is used in every mode except crank, wide open throttle and under 1200 RPM decel(I think), but the book says you don't get a true closed loop until operating temperature. And even a closed loop, has different sensor inputs and ECU outputs depending on the mode.

Click to expand...