ECU wiring prob, little help?

[86turbo]

Hello,

I have an 85 coupe that has the is still using the factory dash harness but the engine harness is from a 93 efi car. Got the car running, everything is fine, however I am troubled on a small part of the wiring. The brown connector located behind the drivers side shock tower has a gray/red signal return wire that is suppose to connect to a neutral safety switch and pin 30 on the ecu. Without this wire grounded I have found the car will NOT start when hot. It will crank just fine but wont give whatsoever. I've been looking over and over the ecu pinouts in my Haynes book and veryuseful site and cannot figure out exactly how this works. What exactly does pin 30 do? Is this pin suppose to be grounded when you have the trans in neutral while cranking? I see the gray/red wires go to pin 46 on the ecu and I have a feeling this should not be grounded like I have now. Can anyone give me some guidance??

thanks

Drew

 

[liljoe07]

No it should not be grounded. PIN 30 is what the ECM uses to ID wether the trans is in nuetral or in gear.

If the brown connector you speak of is shaped sorta like a triangle, then that's the code test port. That grey/red wire is the signal return circuit that a lot of the sensors use. And its used with PIN 30 on a 5 speed setup with the clutch switch. So when the pedal is down, the circuit is closed and the ECM gets a signal that tells it that the trans is in neutral.

Grounding out that wire is probably throwing the sensors readings off. So don't ground it.

 

[86turbo]

no, I grounded out the signal rtn wire (gray/red) I know this should be a dedicated ground to pins 40 and 60 in the ecu. A resistance check between this wire (at brown 8 pin) and ground gives 4.5k. I think the trace in my ecu is burnt up. My harnesses are brand new from lrs and since the ecu does not need to sig return for anything I will just ground that wire from the 8 pin. I got the ecu used and someone prob tried to read their codes and jumped 12v straight to that wire and burned it up in the ecu.

thanks

Drew

 

[liljoe07]

SIG RTN should not be grounded. The ECM does use that source. It goes to the TPS ECT,ACT,EGR,MAP/BP sensors also.

I think I know what connector you speak of, Its a round plug correct?

 

[86turbo]

the connector is a brown, round 8 pin located behind the DS strut tower. It has the oil press, water temp wires that go the inst cluster... ya know?? Maybe the Ford motorsports harness is different than some factory ones? Ok check it out, sig return (gray/red) is common to all engine sensors. It goes to pin 46 which connects directly to pins 40 and 60 (ecu grounds) I just read in another thread where jrichter (sp) was saying how the interconnects that ground out the sig return get burned up by people improperly jumpering for code reading. That is why is mentioned I have so much resistance between sig return and ground. It should be zero, hence grounded. I don't see the issue with grounding the return circuit to the body until I have a chance to properly repair the interconnect in the ecu.

 

[liljoe07]

Ah, I see what your saying now.

You could try and run the codes, that will tell you if the ECM is burnt or not.

 

[86turbo]

well, the car runs fine. I just replaced my engine/injector harnesses with some new stuff for piece of mind. The car ran fine before and it runs fine now only when that return wire is grounded, haha. I think the ecu is fine, it just needs a little tlc when I have the time....

thanks for your help

Drew