When does the ECM kick in?

[Peer81]

Hello,

I'm looking for all the variables to be in order before the ECM goes into closed loop.

I know the O2 sensor should be sending data (after it warmed up).
The coolant should be at a min. temp. But what is this temp?
Maybe there is a min. time the engine should be running?
Any more?

Greetings Peter

 

[Rex S]

ECM "wakes up" when you start the car as it controlls the engine. Maybe I don't understand the question?

 

[Tim81]

Peter, I'm not an expert but here is the way I understand the ECM. The engine will run in open loop until the correct operating temp is reached, somewhere around 190 degrees coolant temp, I do not know the exact temp. Once at the correct temp the ECM switches to closed loop mode and the carb mixture and timing are controlled by the ECM from data received from the MAP sensor and O2 sensor. Hope that helps, maybe someone else thats more knowledgeable will chime in...Tim

 

[Peer81]

Your correct Tim,

But the ECM will look at more things then only the coolant temp. Like I said also the O2 sensor should be working (at operation temp). And maybe something extra.
Thing is, I would like to know the exact coolant temp the ECM wants to have.

I replaced the 180 thermostat to a 160 degrees. But I'm having a hard time to get the engine to operating temp so I can set the carb just right. Going to switch back to the 180 this weekend and see if the engine will get a little hotter.

Greetings Peter

 

[Tim81]

Peter, funny you should mention the thermostat. When I first purchased my car it had a lot of trouble running in "open loop" mode most of the time and the trans TCC would rarely lock -up. I removed the thermostat and found it to be rated at 160 degrees, the service manual calls for a 195 degree thermostat. To make a long story short I installed a 195 degree T/Stat and now everything is fine including the TCC. According to the manual when the coolant temp is above 150 F degrees and the O2 sensor is above 600 F degrees the ECM switches into the "closed loop" running mode.

Regards Tim

 

[Hib Halverson]

Closed loop in the 81 system comes with the coolant temp gets above 150 and the O2S gives useful data.

The manual doesn't clearly explain that the system cannot measure the temperature of the oxygen sensor. The 600° number is cited because that is about the temperature that the sensor tip needs to be before it can start providing useful data.

With an 81, the combination of very slow processor clock speed (so slow, they benchmarked them with a sundial) the O2 sensor sometimes cooling at idle to the point that useful data is not transmitted and a 160 thermostat may have the engine rarely entering closed loop.

My guess is an 81 is going to run best with a 180 'stat.

 

[Tim81]

Closed loop in the 81 system comes with the coolant temp gets above 150 and the O2S gives useful data.

The manual doesn't clearly explain that the system cannot measure the temperature of the oxygen sensor. The 600° number is cited because that is about the temperature that the sensor tip needs to be before it can start providing useful data.

With an 81, the combination of very slow processor clock speed (so slow, they benchmarked them with a sundial) the O2 sensor sometimes cooling at idle to the point that useful data is not transmitted and a 160 thermostat may have the engine rarely entering closed loop.

My guess is an 81 is going to run best with a 180 'stat.

I agree 100 percent...

 

[GerryLP]

Tim.

I presume that when you say the, "service manual", that you mean the shop manual for the L81, but for the life of me, I have been trying to locate that spot that says what the thermostat should be rated at, and I have not found it....could you lend a hand, pal?

GerryLP:cool

 

[redvett]

I have done several 81 & 82's that i installed a heated O2 and solved the drivability problems. The heated O2 will keep it in closed loop.

 

[Tim81]

Gerry,

I am mistaken, you're right I can not find the thermostat spec in the Shop Manual. I know I found it somewhere stating it should be a 195 degree stat. If I can verifie this I'll let you know my source. I'm sure that a 195 stat is correct..... Tim

Tim.

I presume that when you say the, "service manual", that you mean the shop manual for the L81, but for the life of me, I have been trying to locate that spot that says what the thermostat should be rated at, and I have not found it....could you lend a hand, pal?

GerryLP:cool

 

[GerryLP]

I know that I remember testing the thermostat (and recently at that), and now I cannot find it...:L , so it is probably there buried in some little corner in a chart or something. Thanks for checking!

GerryLP:cool