This is one of the nagging little things you spend time trying to "tune out" so I thought I'd reach out. It's a temporary issue that doesn't affect driveability but I guess I like the idea of a nice smooth warmup.
Basically, as the motor warms up, it hits 48-50C and AFR climbs from low 13s
up to 16-17. Playing w idle VE appears to shorten the time span that the AFR stays lean, but it still goes lean for 10-15sec. This takes place as I can see the
ECM going Closed Loop at that coolant temp. Does this have anything to do with the PID controls activating w C/L? This is on an LT-5 using a $D0A mask.

 

Had the same issue on an LG4 engine I converted to TBI. All I did was to bump up the closed loop enable CTS threshold. It just didn't like being in closed loop at that temperature.

The disturbance only lasted for about 30 seconds or so.

Also check the SA CTS & VAC compensation table. Usually right around that temperature GM likes to reduce the spark timing same (at normal loads). This is done to dump heat in the exhaust to get the cat-con up to temperature.

RBob.

 

RBob,

I was heading that way since it seemed to happen consistently right at the 47-48C point. The WB shows AFR going to 17 and then dropping back down to 14.7-15.3 after a few seconds. The only parameter value I could see that was close to that was the CTS Threshold temp for HOT MAT. There is a timer for the Hot/Warm/Cold MAT for C/L enable where the cold MAT is set to 20C and the timer is 30sec from that point. So I am wondering if the combo of the two creates the C/L entry point at about 50C? Would seem that in cold weather, it would try to go C/L at an even colder temp. Recall, I also have the MAT converted to IAT.

I also took a look at the SA v Cool Comp table and decided to throw in another degree around those temps.

 

These are the ones:

CLSD LP - CTS Thres for Hot MAT
CLSD LP - CTS Thres for Cold MAT
CLSD LP - MAT Hot/Cold Thres for CTS

RBob.

 

RBob,

What do you think of using

CTS Threshold for Hot/Cold Timer (Bump up the Cold CTS)
Time for C/L Hot/Warm/Cold CTS (Increase the time for C/L in Cold CTS)

I'll be trying this strategy later today.

 

It depends upon the MAT temperature and what the CTS & MAT thresholds are set to.

The MAT threshold defines which of the two CTS thresholds are used for closed loop enable.

RBob.

 

Well just came back after loading new bin and startup. It worked. Got passed the 47.75C point and no stumble. Viewing the WB, I could see it stayed in O/L then got in to C/L at about 68C. It went a bit lean momentarily but then stabilized. Overall, warmup went pretty smoothly. Granted its 85F in the garage but that allowed it to warm up faster. I've attached a screenshot of TPRT w the parameters I changed. You can see the stock values as well.
So IIUC, as we see in the screenshot, the threshold for Hot/Cold MAT is set at 4.25C. Above that point, ECM did use 47.75C and now its 57C for the C/L timer, which at cold CTS, will be 50sec. I didn't include one other parameter which is the CTS Threshold for Hot/Cold or 70/29C. Anywhere in between is considered Warm.
I'm assuming that the timer doesn't change once its tripped. IOW, if it starts at Cold that's the timer, it does not change as it transitions from cold to warm for example.

 

Yes, it is the start up CTS that is retained and used.

RBob.