Gm Controllers

[peter paul fenske]

Hi Vance and George

The egr in these things up to 89 or so will generate a trouble code
if it doesn't get hot enough. It uses a thermal switch. When the computer
commands egr , shortly thereafter it will check for the thermal switch to
be activated. If not a code 32 is the result.

I presume a cat is not used. Thus without any backpressure the egr
operation is different than originally planned.

Tinkering with the switch location might help. Also in the code the eror table 
can be modified but I have yet to try it.

Also make sure that the PW modulator for the egr gets ported vacum. Do not
directly connect vacum to the EGR. Use a mytec pump to check its operation.

When a TPI vehicle is run without a cat, perhaps souped up a bit with headers
it will tend to run lean in open loop modes. These are wot and start, and warmup
modes. If you want to fix this you can enrichen the mix by increasing the
fuel pressure to about 50 PSI. Closed loop should easily handle this with
the block learn.

Otherwise you will have to get into the code.

Egr operation for 90-92 is simpler. The ECM activates the egr at 50 MPH or so
and looks for a corresponding change in Map. Thus you don't have to worry about
a silly thermal switch.

To change to a 90-92 730 ecm you need to purchase one C-D 32 pin connector 
from GM and one Map sensor. Use the previous post to defeat VATS.
Use a 91 camaro wiring diagram to upgrade yours. 

GL: peter

ps i need a MAF when you are finished.