PCM/Laptop Connection issue

[paulmon]

I've got a 94 OBD1 and a USB to ALDL cable. This used to work and for some reason now can't get the laptop to connect to the PCM. Tried a couple of different application and no device. USB cable drivers are installed and app see "COM3" but doesn't see the PCM.

As the engine was a swap I'm going to make sure the wires going into the port haven't come loose, or frayed.

While on the topic, anyone have a copy of FreeScan? Seems Andy's website is borked.

Cheers,

Paul

[bobdec]

You need one wire to the PCM "serial data" ALDL pin M to PCM pin D30 and you need ALDL pin A tied to chassis ground. Other wires in ALDL go to air bag,Traction Control, ABS and keyless entry modules. They are only required if you want to communicate w/those modules. 99% of connection problem are the s/w setup, assigning ports, drivers, correct selections on the S/W. What have you tried so far ??
As far as Freescan.. Let us know if this works ... FreeScan | Free Communications software downloads at SourceForge.net

[bobdec]

Does your PC have USB port assigned to Com 3 in device manager screens. Connection only requires two pins in ALDL, Pin A to chassis ground, and Pin M (Serial Data) to PCM pin D30. What operating system are you using and what apps have you tried.
As far as Freescan, try this , let us know if it works OK.. FreeScan | Free Communications software downloads at SourceForge.net

[cocobolo95]

If you can't get freescan anywhere else, pm me with your e-mail address and I'll send you the program.

[paulmon]

The USB to Serial seems to work perfectly as COM3 shows up. So I'm convinced it's something with the ALDL port itself, granted I guess the ALDL cable itself could be bad beyond the USB portion.

I've got a 12 PIN plug since the wiring harness was custom made a couple years ago. I'll verify the PIN outs on my ALDL port, I see three wires, not two. I'll use my multimeter and check the resistance to verify that PIN 30 is going to the correct PIN on the PCM and it isn't broken and that ground is good.

The Freescan on Source Forge does indeed seem to be the correct one I found that earlier with a little Google magic myself.

Paul

[bobdec]

You said "I see three wires, not two " To clarify there are 4 (four) stock wires in the ALDL connector. 'A' BLK/WHT to ground , 'B' WHT/BLK to pcm D20 used for high end Service Enabling / Dealer/plant use only. 'G' BLK/WHT to Keyless entry module, 'M' TAN to PCM D30 and also spliced to ABS/TC and SIR (air bag) modules. You only need A & M to communicate w/PCM however make sure the splice if there is one on the TAN wire to ABS/TC/SIR is not holding serial data line down.. Since you cable is custom the colors may not match..

[paulmon]

Originally Posted by bobdec

You said "I see three wires, not two " To clarify there are 4 (four) stock wires in the ALDL connector. 'A' BLK/WHT to ground , 'B' WHT/BLK to pcm D20 used for high end Service Enabling / Dealer/plant use only. 'G' BLK/WHT to Keyless entry module, 'M' TAN to PCM D30 and also spliced to ABS/TC and SIR (air bag) modules. You only need A & M to communicate w/PCM however make sure the splice if there is one on the TAN wire to ABS/TC/SIR is not holding serial data line down.. Since you cable is custom the colors may not match..

Yes, I seem to have wires B, A and M. I connected wires directly into the ALDL port for serial and to chassis ground last night and ran that to my adaptor on the laptop, nothing. This meant B and A weren't connected just A and a wire directly to a good chassis ground.



So I suspect something wrong with the serial wire coming from the PCM. I know that's "pin 30" but what connector is that? Once I find it on the PCM I'll use my multimeter to see if there is any undo resistance along that wire.

Paul

[bobdec]

Some stuff to read.. From shbox.com.. 4th Gen LT1 F-body Tech Articles and http://shbox.com/1/DLC_wiring.jpg . here are a couple of threads on the topic ecm pinouts and Bench Top PCM Programming Wiring Harness Schematic .
Note on the last link (benchtop harness) First the schametic of ALDL to fuses and other stuff is not for for a '94 F-Body, but the wiring from ALDL to PCM, and battery to PCM are correct. Also notice the TWO PCM pins for serial data D29 OR D30. There is confusion on this as all the books say D30, but some fourum posts say D29 and ther is no D30 pin ??.. Also The stock '94 PCM has Two ground points.. 1- a stud on the block near the starter with one black wire, and... 2- Two wires on a ground stud (stud has 4 wires, one black wire to coil/ICM, one strap to chassis and the 2 wires to PCM) that is on the front of the left (drivers) head. All these grounds go to PCM pins A2, C32, A18 and D1 again verify those pins are all good if you can..

[paulmon]

Originally Posted by bobdec

Some stuff to read.. From shbox.com.. 4th Gen LT1 F-body Tech Articles and http://shbox.com/1/DLC_wiring.jpg . here are a couple of threads on the topic ecm pinouts and Bench Top PCM Programming Wiring Harness Schematic .
Note on the last link (benchtop harness) First the schametic of ALDL to fuses and other stuff is not for for a '94 F-Body, but the wiring from ALDL to PCM, and battery to PCM are correct. Also notice the TWO PCM pins for serial data D29 OR D30. There is confusion on this as all the books say D30, but some fourum posts say D29 and ther is no D30 pin ??.. Also The stock '94 PCM has Two ground points.. 1- a stud on the block near the starter with one black wire, and... 2- Two wires on a ground stud (stud has 4 wires, one black wire to coil/ICM, one strap to chassis and the 2 wires to PCM) that is on the front of the left (drivers) head. All these grounds go to PCM pins A2, C32, A18 and D1 again verify those pins are all good if you can..

Great stuff. I've spend a great deal of time on Shbox. I think for starters I'll find the serial pin and check it is whole then move onto the ground wires from there.

[paulmon]

I didn't get to troubleshooting this over the winter, but spring is almost in the air.

I have a theory, my LT1 was converted to coil on plug using the Bailey LTCC. My coils are installed right next to the PCM, would this potentially cause issues with the serial port? Interference? This used to work and thinking today I believe the last time my laptop worked with the diagnostic port was back before I had don't the COP conversion.

I've attached a picture of the coils and their proximity to the PCM.

Thoughts?

[Mystery Bird]

I had this happen to me once. I was at the track tuning in between runs when PC lost connection and fried PCM. Eight hours of troubleshooting later I found my serial wire near the PCM was partially cut. So check that wire all the way from DLC to PCM for continuity.

[paulmon]

Originally Posted by Mystery Bird

I had this happen to me once. I was at the track tuning in between runs when PC lost connection and fried PCM. Eight hours of troubleshooting later I found my serial wire near the PCM was partially cut. So check that wire all the way from DLC to PCM for continuity.

Yeah I'm going to do that, unfortunately the wire for serial is on the one connector on the PCM I can't get off easily. Need to unbolt my PCM which is a pain in the ass. Will do it in the next day or so.

[paulmon]

FIXED!

Tested the ground wire and had no continuity, replaced the wire and presto, data logging works!

Mental note, even with the garage door fully open I don't recommend running a cat-less car inside the garage. *cough* *cough*