Hi,

I have the 305, 4bbl engine in a 1987 Firebird base.

When I insert my 2500 scanner, using the proper aldi connection and 12 volt power to the GM1 connector, the scanner reads correctly, however the engine light will faintly blink and the engine will run slightly rough. As soon as I remove the scanner, engine goes back to running smoothly. Any thoughts?

And I have searched for info on what is the difference between closed and open loop. I am confused on it.

Thanks in advance,

Louis

 

The faintly blinking SES is normal when reading the ALDL data. The ECM SES output is wired through a lamp driver module that also provides for the ALDL serial data.

The engine will run differently with the scanner connected as it is programmed into the ECM. I've worked on a couple of CCC setups and this is an issue with troubleshooting.

Open loop versus closed loop fueling. Closed loop uses feedback from the O2 sensor to adjust the AFR. Open loop doesn't.

RBob.

 

Hi Rob,
Thanks for the reply. I am still a bit confused on open vs closed loop. What indication, if any will I see in either loop.

Many thanks,

Louis

 

There should be a flag in the ALDL data stream that shows open or closed loop. You can also look at the INT, if it is other then 128 that would signify closed loop. Although CCC systems a a bit different then the EFI I'm used to, this information may not be available in the CCC systems.

RBob.

 

Thanks again, Rob

Louis