Trouble with ALDL connection on mock setup

[Guest]

I finally wired up my 727 ecm and programmed a chip with the code. I made an ALDL cable interface using the 25 pin plug instead of the 9 pin since that's what I had. I was just told it will not work with that plug even though the diagram tells how to wire it, so I'll be changing that shortly.

In the meantime I still haven't been able to send the ECM into diagnostic mode, the light comes on with power but doesn't flash when I ground terminal B (white wire blk stripe) to the negative terminal of the power source along with the ground wires so anyone with some idea of what's going on by all means share.

[bszopi]

I think it has something to do with the proximity of the pink flowers... :P

I'd have to look at some other diagrams, but could it be that it needs to be grounded via the ECM? Without looking into it further, I can't say if the ground pin to the ALDL port comes from the ECM or if it goes directly to chassis ground. If the is via the ECM, there might be an internal resistance issue that is stopping it from going into diagnostics mode.

[Joseph Upson]

Must be something I'm not doing right because I have powered up 3 different computers and no flash. I don't think it needs to be grounded to the Ecm specifically because the ECM case wise anyway is not grounded to the vehicle. Maybe there is a specific sensor ground or signal that is not tied into the ground loop causing the failure to flash codes.


I'm more interested in be able to connect to the ECM and monitor values so I hope to get the proper cable some time before the end of the day.

[bszopi]

The reason I brought it up was when I was working on swapping in a '9396 ECM to control my 3100. We were getting some wierd readings while datalogging and ended up that I abandoned the project. A few months later it was brought to my attention that specific sensors have to tie into specific grounding points or the signal produced will not be accurate/correct. I think it was the MAP sensor in my case that I didn't have tied in right. So that is where I was coming from with that thought...

[Joseph Upson]

The reason I brought it up was when I was working on swapping in a '9396 ECM to control my 3100. We were getting some wierd readings while datalogging and ended up that I abandoned the project. A few months later it was brought to my attention that specific sensors have to tie into specific grounding points or the signal produced will not be accurate/correct. I think it was the MAP sensor in my case that I didn't have tied in right. So that is where I was coming from with that thought...

That has been my growing suspicion from the start so I believe I'll make one more attempt after converting from the 25 pin parallel port wiring to the DB9 wired ALDL cable and after that just take everythint out to the engine stand and wire up from there with sensors on the engine. I have had the same results over 3 different ECMs now.

[armyBob]

That has been my growing suspicion from the start so I believe I'll make one more attempt after converting from the 25 pin parallel port wiring to the DB9 wired ALDL cable and after that just take everythint out to the engine stand and wire up from there with sensors on the engine. I have had the same results over 3 different ECMs now.

What software are you using? I never had to put my ECU in diag mode, it seems to be sending the data stream all the time.

I'm in Tampa too.