Is there a way to wire up an LED to tell me when the car is in both closed and open loop?

 

Nope, just need to use a scan tool.

 

Sure there is. I think Willie (this is the second time I've mentioned his car. I think it's my hero..hehe) has one that monitors the Air Control Solenoids. When it bypasses the air flow to the cat, that's a fairly good indication of closed loop operation, and he has an LED that shows when this happens.

If you're just doing diagnostic, and not talking about a permenant LED display for that, you can put the car into field service mode at the ALDL connector by grounding the B terminal to A. This will flash the SES light; if it flashes quickly, it's in open loop. If it flashes slowly, it's in closed loop. It can also show you whether it's running rich or lean by how long the bulb stays lit during the closed loop flash. Lit longer means rich.

 

Actually, Jza, I'm asking this question because I saw that on Willie's car too . This would be a permanent installation... Would I just wire up a relay in a circuit to those solenoids to enable/disable the LED(s)? Do you have a picture of the solenoids and maybe a wiring diagram of them?

 

The air control solenoids is the Princess Leah looking thing on the passenger side just above the smog-pump. It's got a black connector, and a grey connector. The black connector is the divert solenoid (diverts air to the converter). Now you could splice in the wires for the LED here, and it would be a little more obvious what the function of the wires are. Pin A on the black connector is a switched 12v source from the gauges fuse (on with the key). Pin B, is grounded by the ECM. If you wire the LED circuit in parallel with those two wires, it should light when the solenoid is activated.

You could also tap into the wires inside the car. Assuming you have an 86 with the stock computer, it will be a black wire with pink stripe going to pin C2 on the ECM. That will be the (-) connection on the LED (the LED will probably need a resistor in series). Connect the (+) post on the LED to a switched 12v source. Gauges fuse is a good spot.

For the "open loop" indicator, you can use the ALDL connector pin C. That's a second ground path for the port solenoid (the other grey connector). Running 12v through an LED (with resistor) into it should do nothing unless the port solenoid is activated by the ECM, in which case the LED lights. Grounding it will activate the port solenoid. If you're gonna tap in near the ECM, that's pin A2 on the ECM.

Here's a diagram, but the divert solenoid pin labelling is incorrect. The top one should be "B" and the bottom one should be "A". I think this was deadbird's little drawing, but I'm not sure.

 

Thanks for being so helpful, Jza! I'll wire those two LEDs up once I get my custom indicator panel installed.