Everyone has said how the factory calibrations run on the rich side. To be honest, I never bought into this, because every stock GM vehicle I've scanned has typically had BLM's in the 130. So, this never made sense..

...until tonight. I scanned two runs at the drag strip, and holy smokes! The ECM is trying to run the fuel ratio as rich as 11.2:1!! I know this is an open loop "guestimated" AFR, but wow.

Is this what everyone's talking about when they say factory calibrations are too rich?

The sad part - even running this rich, i'm still averaging 2.6 degrees of retard across the entire run.

Guess it's time to go search the archives for tips on WOT tuning, but any comments are welcome...

 

Typical of being in cat-con protection mode. They (GM) floods
the cat with fuel to keep the temperature down.

RBob.

 

Anyone else? Glenn? Grumpy? Is this what everyone means by the stock gm calibrations being rich? Do you really need to flush this much fuel through the converter?? Any ideas why it would have knock counts and timing retard - false knock? or is this normal?

 

I believe the stock VE tables (AUJP 1350) run fat through the midrange. When I installed my offroad pipe (read here deleted my cats), my car would give off fumes in certain driving situations. reving it up and steady loads at cruzing speed seem to be the worse. I first turned my attention to the O2 sensor to verify it was working properly and that an exhuast leak was not messing with it. Next I checked and replaced my vacuume lines and checked for intake leaks. After fixing thes thingas and verifing all was in working order I proceded to modify my eprom.

1. leaned out the enrichment based on operating engine temp. This is equivelent to a choke on a carb and GM leaves the choke on almost all the time on stock memcals
2. Fattened the lower VE tables to compensate for Choke modification.
3. Proceeded to lean out the midrange load and RPM range of the VE tables.
4.To compensate for the enleanment I started adjusting the timing back.

I suggest you study up when leaning out an engine. Going to far lean is the quickest way to burn it up. I will also state that I performed these steps on a stock 91 speed density 350 auto GTA. I am not in anyway declaring I know what I am doing or that these are the right steps to take for your own car. Any conformation would be appreciated

 

Yes, the cals are rich.
Even using the commanded 14.7:1 AFR is richer then it needs to be.

The 128-130 is so minor as to not be an issue, the issue is that the engine is richer then what it needs to run at.

At WOT the 11.2 commanded is again too rich. For cat protection as RBob mentioned and it's cheaper for warranty to change spark plugs rather then engines.