Renix wont go into closed loop (O2 sensor) mode

For my 1990 Renix six cylinder, I have a SnapOn MTG2500 scantool attached for trouble shooting. The scantool tells me the ecu is staying in open loop mode.

Per the scan tool...
a. The O2 sensor is operating, fairly steady at near 2.5 volts or so at warmed up idle, and does increase when motor is reved. the O2 sensor is fairly new only a few thousand miles on it.

b. Both short and long term fuel trim is at 128, which I understand to be correct for open loop operation

c. coolant temperature is 187F

b. injector pulse is about 5 when warmed up at idle, when cold shortly after start it was about 9.

What might be the problem that is preventing closed loop operation?

Thanks!

Not getting to temp will definitely do that!

Is not 187F not enough? I drove her 2 miles then idled for near 20 minutes, she reached 187F after 10 or so minutes, then no longer went higher. I have a 195F thermostat per the factory manual. Must I be at 195F for closed loop to kick in? Note the 187F is from the ecu via the scan tool.

At what temperature does the ecu need for closed loop operation?

I suppose I can fool the ecu into thinking the engine is hotter by substituting an appropriate resistor or pot for the coolant temp sensor and see if the ecu goes to into closed loop mode, or drive her more to try to get her hotter. The temperature here is in the high 40's last night when I did the testing.

thanks!

Ok, I drove her and got her more warmed up, below are the scan tool results at idle...

rpm....589
O2 volts...3.59
Inj Pulse mSec...10.4
Loop Status... Open
Exhaust...Lean
St Trim...128
Lt Trim...130
MAP Volts...3.6
MAP Hg...23.1
Man. Vac Hg...8.0
Baro Press Hg...30.8
TPS Volts...0.70
Throttle Sw... Closed
Throttle %... 14
Fuel Sync...neg.
Coolant Temp F...203
Charge Temp F...235
Spark Adv btc degrees...19
Knock...0
EGR...Off

Now I have tied two different ecus, and two different MPS My MAP voltage seems high, as the manual claims it should be 1.5 to 2.1 volts at hot idle

I also noted that at hot idle when I restart the motor, the idle can dip down to 450 rpm or so, and when it is below 500 rpm the ecu will go into closed loop mode temporarily, then the idle will surge to 1200 to 1500 after 5 to 10 seconds and at that time she goes into open loop, if she drops again to less than 500 she goes into closed loop ( or she goes into closed loop which then makes her go to below 500 rpm) this may cycle several times, then stabilize at 600 or so rpm and open loop operation, until I turn her off and then restart.

I drove on freeway while monitoring, and she stayed in open loop the entire time.

Suggestions?

I'd check for exhaust leaks, maybe a cracked exhaust manifold.

Found a huge intake leak! We used a smoke machine got a lot of smoke out the tail pipe. Then blocked the tail pipe and saw smoke coming out the egr stem. Removed the egr, and the egr valve seat fell out. thus the egr was never closed in fact the loose seat was propping the valve open! the seat had been swaged into the body of the egr, but came loose.