Quote Originally Posted by In-Tech View Post
Yes, I'm not sure LT1's ever had an EGR circuit that was active, however, all other ecm's have quite a few separate "tables" when the EGR is active. Or I should say, when the ecm thinks the egr is active.

I read all the time where people block their egr and wonder why they have a part throttle lean and knock issue. IF THE COMPUTER THINKS THE EGR IS OPEN IT PULLS FUEL AND ADDS TIMING!!! These are tuneable events and corrections. Changing a cam/exhaust/heads etc drastically alters the egr qualities.

Some egr's are basically on or off, other later ones are pulse width modulated and there are even more fuel tables and spark tables to work with that.
By comparing the 1996 LT1 tables (which had an EGR) with the 1996 LT4 tables (which did not), we can see how the LT1's PCM handles EGR events.

The obvious differences are the EGR-related error codes. Easy enough to disable, but only gets rid of the MIL. The LT4 sets the enable temperatures high to disable EGR but otherwise leaves the settings within sane ranges (Min MAP 22.2 kPa, Min RPM 900, Max RPM 2300, Enable Speed 8 MPH, Disable Speed 6 MPH...Enable Coolant Temp 151.25C). EGR Spark Advance is set to between 0.0 and 1.0 (odd they didn't just zero out the table). Those are the only differences between the two calibrations with regards to EGR operation.

It would appear that merely making sure that the EGR enable values are out of a sane range is enough to disable all EGR-related changes. GM certainly seemed to think so.