Can anyone give me a hand. I have a 90 camaro with a 7730. My computer will not communicate with my aldl port when the key is turned over but will connect for 3 seconds when the key is turned to the off position before giving me a error message. I tested the volts on the data line and had 5.1 when on an when turned off it would be 4.9 for about three second before dropping off to 0 I've swapped the ECM out to no avail. What does the ECM need to initiate data out? Does someone have a schematic for the ECM/aldl port and know what I should look for as far as communicating data to the aldl port?

 

Well, the ALDL is 8192 baud at 8N1. It is a 0 - 5 volt interface, otherwise standard serial data. So need a cable that will convert from 0-5 V to RS-232's -8 to +8 volts. Or to USB if no serial port.

The PC needs to send a data packet request in order for the ECM to send one.

RBob.

 

The problem I am having is that the cable won't read anything unless the car is turned to the on position and then back to the off position. This is the second cable i have gotten and has done the same thing. It last for approx. 2-3 seconds. I've used both tunerpro and ttdatamaster for the $8d. They don't connect at all while the car is in the on position when it goes to the off position it connects transmits then loses the connection. I have a feeling that its the ground on the aldl port which I don't know where it connected. But it has continuity when no power is applied. When the key is turned over and power is applied it loses continuity and has a massive amount of ohms. I read somewhere that all you need is the ground and serial line to transmit is that correct? Where is the ground located at on the aldl and what would cause an open circuit when the key is turned to the on position

 

Ground on the ALDL connector (pin A), goes out the bulkhead connector (fuse block area), gets tied to the engine block, then circles around to the EFI harness and back to the ECM.

At the ECM it could be on pin A12 or pin D1.

Check the grounds on the back of the heads.

RBob.

 

http://postimg.org/image/c40nw93jt/

Soo there are three black and white wires one tan wire I'm guessing all grounds. I'm also guessing they were ripped out during the engine swap. What do they go to so I can better wrap my head around the problem I know one is the ECM and the aldl port I'm not sure about the other two?

 

They are EFI system grounds. They could be ground references or even the grounds for the injector drivers.

The tan wire is the O2 sensor amplifier ground reference (in the ECM).

RBob.

 

It was the ground. Thanks.