Hi

I am having trouble with my 89 Suburban 5.7L TBI.
I can not get a code 12 ( or any other code ) from the system.

Original ECU blew the ECU-B fuse instantly.
Replaced ECU and got a solid CES light on ignition on.

I have followed chart A-2 all the way down the left side.
I get 5v out of Diagnostic pin (pin B) on ALDL connector.

When I ground Pin B, either to Bin A or another ground point
I get a quick CES light, a short no light, then a solid CES light.

I have replaced ECU with another (3rd) unit with no change in behavior.
It seems unlikely that both replacements... junk yard pulls ... would exhibit same error.

What Now????
Do I need to probe some of the connectors right at the ECU?
Maybe Diagnostic to Ground?

Should I try reading serial Diagnostics from pin E ?
I have not tried as I am assuming that if the check engine light diagnostic is not working then the
serial ALDL data will also be at fault.

Bob