I've fought this ongoing very rich during warm up condition for years now. I had a junk fuel pressure regulator that was causing high pressure when cold and lower pressure when hot and I thought that was it and while it was a contributing factor it wasn't the whole problem. Basically until it reaches operating temp (180 degrees and stays there for a while) it wants to run a good 2 points richer then the commanded AFR. I run it in open loop so say on my way to work when its commanding around 16:1 I'm seeing more like 14:1 at the leanest. Getting up to speed I should be seeing around 14.5:1 and I am seeing more like 12.5:1 and its killing my fuel economy. It does this for a good 4 miles before it starts to slowly, steadily, lean out. I would say after a good 7-8 miles and things are finally up to temp. the actual AFR matches the commanded. I've got a big radiator and a 180 degree thermostat and an engine that just doesn't make much heat so it takes a lot of driving to make it finally heat up. I was told there is some sort of table that is basically a correction multiplier over the overall fuel control vs temperature but I haven't been able to find anything. Makes sense that GM would do something like this to richen it way up when cold to go well with that retarded timing to really heat the cat and engine up fast but for my application its not cool at all. Any ideas of what this table is called and where its located at?

 

Timewise, how long does it take? The PCM will initially enrich the engine for initial run, but this usually is out and gone within a few minutes.

 

I would say a good 10-12 minutes. The other part to it is if during this time when its running rich, if I go to WOT it seems to cancel out whatever is making it be excessively rich and then it for the most part the actual and commanded match.