Some may have read my other posts but a quick recap is a TPI motor in a 57 Nomad. I used a S&P stand alone harness and a 730 ECM. The computer goes into limp mode as soon as the key is turned on. It will not communicate with a scan tool, it will not give codes when the aldl is jumpered, the SES comes on and stays on all of the time. I have checked the wiring to the ALDL and it is fine. I replaced the ECM with no luck. I have ohmed out the harness and it all looks good. The only thing that I have found suspious is that the black/red wire to the dist. module shows to be grounded thru the distributor. Is that normal? The black/red wire goes from pin A on the distributor module to pin D9 on the ECM. Please tell me this is the problem so that I can get this going! Thanks for the help. Steve

 

It is a weird problem by your symptoms there. How do you know it is in limp home mode with no info from the scan tool or the SES light?

You never have said definitely that the car runs. Does it??

Your blk/red wire from the dist. certainly would not cause the ecm to not communicate thru the ALDL.

Turn the key on and check for the 5v reference from the ecm. The easiest way would be to pull the TPS connector and check pin C.

If everything you have posted is true, e.g. there are no wiring errors and the ecm is definitely good, then I would start looking at the grounds. Often weirdness is caused by poor or missing ground connections. Go to your wiring diagram and chase down every ground shown. If there are crimp terminals make sure none were crimped over the insulation and not making contact. Ideally, all the grounds should be connected to the same place on the frame. Make sure there is a good electrical connection between the engine block and the frame.

Good luck!

Steve

 

Thanks for the reply. It does run it just runs in limp mode/fail safe model. The way I know it is in limp mode is beacsue the SES stays on all of the time, the timeimg never moves regargless of RPM, and it will run just the same if you completely remove the prom and run it on the memcal. I checked the grounds and all have less than 1 ohm between the harness and frame. The reason I was asking about the dist. wire was I thought maybe I had shorted the origianl ECM thru the grounded wire, then maybe the new one got shorted the same way, but the ground there may be normal. Thanks Steve

 

I checked a distributor I have laying on the shelf and the red/blk wire appears to be a diode inside the module. Low resistance in one polarity and high in the other. Check the resistance with both polarities and if it is greatly different I think you can rule that out as the culprit.

I am skeptical that the red/blk wire could take the ecm out completely. Maybe one part but not the whole thing.

Do you get your 2 second fuel pump operation when you turn the ignition on? Do you have 5vdc going to your sensors? I think there is something obvious getting by us here.....

Steve

 

Are you absolutly sure the memcal is right for your application?

 

No, I am not sure its correct, and I would love for it be something that simple. Is there a part number listing or photoguide I could check to see? Thanks Steve