I am having trouble linking diacom to my 87 vette at 8192 baud (it will link at 160 baud). I went to the the diacom website and found this message:

"1986 thru 1989 Corvettes, Camaros, and Firebirds with 5.0L and 5.7L engines are equipped with engine control modules which require a special diagnostic adapter for high speed communication. Are you using Diacom's special TPI diagnostic adapter (part number 91006) ?"

Does anyone know what is in this special adapter?

Thanks,
Mark

 

It is an adapter that plugs in between the 2 cords. It contains a 10k ohm resistor which the ECM needs to trigger the tx/rx function in the ECM. It's a must for Diacom to work.

Frank :flag

 

Yeah its the one that says "TPI" on it.

 

The 91006 adapter looks exactly like the black 91007 adapter except that it says "GM SPECIAL - TPI" instead of "GM 1982 & Up". I needed one for my '89 and ordered it directly from Rinda Technologies (773 736-6633) for $24 plus shipping last year.

Hope this helps! :seeya

- Greg Smith, '89 Coupe

 

Greg and Brian are right, but this can be confusing. With Diacom, one cable is an ALDL connector at one end and a 5 pin DIN connector (Old PC Keyboard style) on the other. It will be Diacom #91006 or 91007. The confusion comes from GM moving the ALDL serial data pins around. Diacom expects the serial data to be on the 3rd pin of the 5 pin DIN connector. The 91007 cable wires this pin to ALDL pin L and M, where serial data is present on '90 and up OBD-I. If this cable is used with an earlier car, and that car's ECM is in other than Diagnostic Mode (low speed data), there is no data for diacom to link to on DIN pin 3. What 91006 does is wires DIN pin 3 to ALDL pin E. This is where high speed data is on '89 and earlier Corvettes. What Frank mentioned is an adapter that is DIN 5 pin male on one end and DIN 5 pin female on the other about 2 inches long. What it does is crosses DIN pin 3 to DIN pin 5 or 1 depending on where you start counting. Pin 5 is unwired on the 91006. This effectively gives you the 91007 and 91006 in one neat package. Depending on when you bought your Diacom, you either got a 91007 with the little DIN adapter or got the 91007 and had to order the 91006 to get high speed data frrm '89 and earlier. Where Frank went wrong is in the 10K Ohm resistor. It isn't in the adapter. The other Diacom cable, the one with the DB-25 connector at one end that connects to your computer's parallel port and the 5 pin DIN at the other houses all the electronics. When you change modes in Diacom a different resistance will be placed across pins 1 and 4 of the 5 pin DIN connector. When connected to the other Diacom cable this resistance will be seen at ALDL pins A and B. 10K Ohms is one resistance for one mode. Diacom can also short these pins (0 Ohms) and effectively does what you do with a paper clip when extracting codes.

Hope I haven't bored everyone to tears.

 

Last night I modified my interface cable. Adding a switch to short pin 3 (aldl E) to pin 5 (aldl L,M). Linked perfectly. Now I can just flip the switch to change between the two connector types.

Thanks for the info, saved me $25.

 

No problem, glad someone found the info useful.