Coolant Temperature for entering closed loop

[Ronnie]

7 minutes ago, 2seater said:

Minimum temperature for closed loop is only 32*C?

That's odd. I've never saw mine go into closed loop at less than 168*F. I wonder if the '90 is different. Mine will allow the converter to lock at a little less than 168* but the closed loop indicator on the CRT doesn't light up until about 168* if I remember correctly.

[2seater]

1 hour ago, Ronnie said:

That's odd. I've never saw mine go into closed loop at less than 168*F. I wonder if the '90 is different. Mine will allow the converter to lock at a little less than 168* but the closed loop indicator on the CRT doesn't light up until about 168* if I remember correctly.

I have never watched in detail for something like that either, so I don't know what to make of it. I know the closed loop threshold seems to be different from year to year, or maybe calibration to calibration in the same year. I am trying to imagine how fast the engine warms up from ~90*F to 153*F in this case. Two minutes, more, less?? Stuck open thermostat = no closed loop?? 

Edited June 23, 2023 by 2seater

[Ronnie]

Maybe my memory is failing. The last time I checked the temp for closed loop was several years ago when I installed the 170* thermostat. I could have been wrong about the temperature. The next time I have the Reatta out I'll try to remember to check it again. I do remember when I was checking it before the temp outside was cold. I was worried the it might not go into closed loop in cold weather with the 170* thermostat was the reason I was checking. What I remember is it was just barely getting into closed loop with the 170* thermostat. Could another sensor have been holding off from going into closed loop as quickly as yours? Maybe the temp sensor in the air box?

[2seater]

Honestly, I do not know all the interplay between sensors and programming and overrides and redundancies. I doubt any one sensor will keep the closed loop from happening, but maybe the O2?? It simply is in the interest of emissions to having it run in some sort of feedback mode whenever possible. I was surprised by the result as well and I may try it again tomorrow with a cool engine.

[2seater]

Okay, I tried it once more with the knowledge of what I learned yesterday:

Ambiant temperature 65*F

Cold start after parked overnight. Started and let it idle which started at 1200 rpm 

23*C by the time I got to ED04 and started stopwatch less than 30 seconds after starting

35*C @ 2:03 minutes and first segment lit on the 1990 temperature gauge

40*C @ 2:34 

Loop light on @ 2:39, or approx. five seconds later. O2 sensor blinking

This matches what's in the chip for minimum closed loop temperature

 

I looked at the 1988 ANCX and ANBM calibration and the cold loop enable is the same 32*C as the stock 1990. The only difference I can find is the 1988 uses a longer 50 second warm loop timer vs the 25 second for the 1990. All other timing and temperature thresholds are exactly the same.

 

Given all of that, it would seem in similar starting conditions, the engine should be closed loop in ~2:30 with a stock calibration

[Ronnie]

1 hour ago, 2seater said:

40*C @ 2:34 

Loop light on @ 2:39, or approx. five seconds later. O2 sensor blinking

I took my Reatta for a drive this morning and did the test the same way and same place I did before when I first installed the 170* thermostat to see when my engine goes into closed loop.

 

I went into diagnostics on the CRT and let it go through the self test. then I went to ED04 (coolant temp). It showed 25*c before I started the engine.  Then I started the engine and with the CRT showing ED04 I headed out on the same route I usually go -- 2 stop signs and then a straight 4 lane highway. I watched as the temp climbed and at 75*c (167*f) the loop light came on and stayed on the rest of the time I was watching it, including some stop and go traffic. When I switched the CRT over to the gauges screen it showed the temp at 170*f as long as I was moving in the cool morning air (74*f). I didn't pay attention to it at stop lights because I new it would start climbing.

 

I can't explain the differences in the temps where my '88 goes into closed loop and your '90 does. I probably have a cooler thermostat but that shouldn't make a difference.

 

Try testing your '90 the way I did while driving and see what results you get.

[2seater]

Mote testing will have to wait. It will be closed loop before I leave the dirt road or it will at least muddy the water. It may be different if in gear or not, I do not know. I do vaguely remember when we were fighting the lack of closed loop and O2 sensor inactivity on the red 89 my son has, after changing the ECM, the loop light and O2 woke up after going only a couple of hundred yards but it probably had some heat in it already? You could always test it the way I did to see if it is different?

[Ronnie]

I will test again  your way when the engine is completely cold.

[Ronnie]

Ok. Did another test. The engine wasn't as cool as I thought it would be but the results were about the same as when driving. I think it probably took more time to get warmed up this morning with the cool air moving through the radiator. I didn't try to time it going down the road.

 

Test 2:

By the time I got to ED04 in diagnostics with the engine running coolant temp was up to 45*C

The Loop light came in 2.47 seconds at 74*C and the O2 light started flashing.

 

I can't explain why my engine doesn't do the same as yours. I'm pretty sure your engine is doing the right thing since you can look at the data tables and know what it is supposed to do.

[2seater]

There may be some hidden instructions in the 88 that I can't see. I asked my son to give the black 88 from Dave a try. It has a freshly programmed Prom and is bone stock as far as I know. I tried my car on the move today as I was leaving my cottage. We just had over an inch of rain in a couple hours so I was just idling out. Start up coolant temp. was 21*C, backed out of the shed, hit the door close button and idled away. Maybe got to 15mph but no more. It is about .2 miles to get to my property line and just as I did so, coolant reached 40*C, loop light came on and O2 started blinking. No apparent difference between moving and static.😎 

[2seater]

Got the chance to test the black 88 of my sons (Daves previously). As mentioned before this is a freshly programmed ANCX Prom. The figures confirm that the 88 is indeed different than my 90. Starting temperature was 28*C, let engine idle as it warmed up. Shortly after 72*C, loop light came on and O2 started flashing. There must be a difference built in that isn't visible or adjustable. Just for interest, if anyone with an 89 would try the same experiment it helpful to see if the 88 is alone or if the touch screen cars are similar.

[Ronnie]

Thanks for testing the '88. The test results being similar to mine tells me that mine is working properly for an '88 model.

[2seater]

Number two son tested the red 89 this morning. Startup temperature of 28*C, one minute forty-five seconds and 33*C = closed loop. Pretty much like my 90, so I do not understand the differences, but with this tiny dataset, it seems there are model year differences.

[Ronnie]

There are so many differences between the '88s and later models. Once the '88s got in the hands of the public and they started getting feedback from the dealerships, the engineers must have saw a lot of tweaks that needed to be made for building Reattas going forward. Some changes I understand, like the axle and hub splines being larger in later model Reattas. That could have been to make them interchangeable with the big Buicks to eliminate parts unique to the '88s.  I don't understand the changes to the ECM chips unless it had something to do with fuel mileage or air pollution. Until we started comparing them I didn't expect there would be a difference.

[2seater]

I would guess that customer experience and feedback played a role as you say. Quicker closed loop would be in the interest of emissions perhaps? The camshaft lift and duration were toned down after 88 as well, despite the internals being otherwise the same. Why? Also unknown.