Swapping out my 1982 LG4 305 for a brand new 383 stroker. New engine will have a Holley Brawler carb on it, which other than the electric choke connection, will not have any electrical connections to it unlike the Rochester that's on there now. There are two connectors going to the carb as shown below that plug in on the top and side. I'm thinking these provide info from the ECM about engine parameters to control fuel mixture, etc. These won't be needed on the Brawler, but will leaving these unplugged throw a check engine light (that I'll have to unplug the bulb for)? As it is, there are so many connections there were left unplugged by the PO when he rebuilt the engine and zip tied to the wiring harness that I have no idea where they originally went. Just hoping this thing will run right when I get everything hooked up. Thanks

 

recommend removing the entire ECM harness as a unit (and storing all of the pieces).

you can pull it through the right fenderwell and pull the ECM as well. either remove the check engine light driver or the bulb as it will light with the ECM gone.

without the carb connections (and the ccc-carb) the ECM will be useless, including the dizzy connections. you'll have to replace the EST dizzy and if auto, wire in an alternate means of controlling torque converter lock.

the choke connection is separate from the ECM harness.

 

Yes, now that you mention it I see that all of the connections on that harness have to do with engine control, like O2 sensor, carb connectors, coolant temp sensor, and then the TC lockout (it's a TH350C) and a couple of grounds. So under my new setup that whole harness is not even needed. I knew I'd have to put a vacuum advance distributor on it. I had rewired the TC lockup and put a toggle switch inline with the brake pedal switch, but now I need to rethink that because with the harness disconnected there probably won't be any power coming to the connector at all. Will have to use another 12v source I guess, still tied into the brake pedal switch.

Luckily I don't have emissions checks in NH, just a safety inspection. Thanks for your response

 

OK, I'm thinking of keeping the ECM installed and tucking the harness into the passenger side fenderwell out of sight. The only reason I'd like to do this is to take advantage of the wiring for the TCC lockup and the VSS signal that is fed to the ECM that will control at what speed the TC locks up. From looking at my service manual, it appears that the VSS, ignition power, brake switch, and gear selector switch are what's providing control of the TCC. "The ECM provides a ground for the TCC solenoid when vehicle speed is high enough." The gear selector switch should still work and remove the ground when in park and neutral. The only thing I'm not sure about is the mention of "when operating conditions such as heavy acceleration indicate that the converter clutch be disengaged, the ECM removes ground from the TCC clutch solenoid". I am not sure how that is done. I am not seeing any vacuum signal in the circuit according to the diagram. But I'd like to take advantage of the existing wiring and the VSS to control when it comes on, and it doesn't appear that any of the other inputs on that harness would affect TCC operation (O2 sensor, Coolant Temp Sensor, carb connections, etc.). You think this might work? I have already confirmed that I have 12v to Pin A on the TCC connector that plugs into the trans and I don't when I step on the brake. I do not have a ground on Pin D but I believe that's because of the VCC not letting the ECM do that because the car is not moving. I suspect that if my VCC works correctly it will send the signal to the ECM and the ECM will provide the ground to Pin D at the appropriate speed to complete the circuit for TCC to engage. Of course, I'll have to lengthen the wires for the harness that goes to the connector, as the harness will be moved back into the fenderwell but that's easy to do. Think this will work? Otherwise, I'll just have to connect A and F on the ALDL to establish a permanent ground to Pin D and control it with a switch.


Thanks, this forum is a lifesaver

 

the ECM determines acceleration conditions through info received from the TPS and VAC sensor. I'm pretty sure it also will not allow lock until operating temp is within range.

you could try a remote TPS but the effort and resources may be better applied to a known work around.

search for alternate means of lock using the a vac switch

 

You are right. The VAC sensor is on that same harness (and bolted to the firewall just behind the brake booster. I'm sure it needs that signal too. Maybe I could keep that in the loop too but there's no fixing the TPS problem as that's in the carb itself which is going away so if that's really needed for the ECM to apply the ground, it won't work. I guess I'll give it a shot and if it doesn't work, I can always ground pin D permanently. I already have a switch installed on the 12v side after the brake pedal switch.

 

you can try it but you'll have to provide the proper voltage across the TPS signal wires to match the throttle position the ECM wants to allow lock up.

with the connector unplugged there will be 0 volts, shorted near 5V. behavior will also likely be sluggish

 

There's no mention of the TPS as an input in the service manual, so hoping that it won't be an issue. With the VAC sensor kept in the loop, I'm hoping that along with the VSS will be enough to tell the ECM to close the ground and enable TCC engagement. We'll see, I guess. It will either enable lockup or it won't. I cant imagine it will be sluggish, as the ECM will enable a ground or not - there will be no in between.