There is so much useful information on this forum and I'd like to contribute. So, I am starting this thread to document the issues I experience with my DX and what I did to troubleshoot and repair it.

Occasionally, the check engine light remains on when I turn the key to ON. When this happens, I can't hear the "hiss" of the fuel pump and the engine will turn over, but it won't start. If I wait long enough, I can hear the main relay click, the fuel pump hiss, and then the check engine light goes off. Once the CEL is off, the car starts without issue. The ECU does not display any OBD codes when I short the nearby two-pin connector. I pulled up the carpet near the ECU to get visibility of the LED window. In normal operation, the red LED blinks once when the key is turned to the ON position. When the CEL stays on, the LED remains off until I hear a click from the main relay which is followed by the LED blinking once. I read this post about cracked solder joints on the main relay which had me convinced it was the relay. I removed the relay and reflowed the solder and reinstalled it. Now the CEL never goes off no matter how long I wait and I figured I just did a terrible job resoldering the points and probably damaged the relay more. I removed the relay and used a 12-V battery from my drill and some jumper wires from my electronics kit and followed the procedure here to test it. It passed the test, which made me suspect the harness next. I used the main relay diagram shown below to reference the pins on the harness. I put the negative terminal of my multimeter set to DC voltage in pin 2 and the positive to pin 5 and read 12 V (key in ON position). I checked pin 7 and saw 0 V. I checked pin 1 and saw 0 V.

Pin 1 says it is the positive terminal of the battery. If that's the case, then I should be reading 12 V at pin 1, but I'm getting 0 V. This leads me to conclude that the battery voltage is not making it to the main relay and thus never reaching the ECU through pin 3. (If you are reading this and thinking I'm the biggest idiot that ever walked the earth, please correct me so I can understand better what I'm working with) Based on my troubleshooting thus far, the most likely culprit is the wire connecting pin 1 to the fuse box...at least I'm pretty sure that's where it goes. I haven't traced it yet and the Haynes manual has a wiring diagram for 1985 through 1987 that says it goes there. I'm done for tonight and will try to dig into this more tomorrow.




Another issue which was much easier to solve was the brake light staying lit when I lower the hand brake. I checked the brake fluid and it is below the minimum. I raised the floater switch and sure enough the light went out. Fix should be straight forward, if I can get it to start.

 

I found the failed component, but it was bitter sweet.

I traced the wire from pin 1 to the fuse box under the hood. When I opened the box I saw that all the connectors were charred. Checking through the circuit I found the fuse for the ECU was open. I popped in another 15 A fuse, turned the key to ON, the CEL turned off, the pump whirred, and the engine started.








The reason I think this is bitter sweet is the fact that I don't know why they got charred and the fuse opened. Since it was the ECU fuse that was opened, I am assuming there is something wrong with that. Aside from figuring out root cause, I need to repair the wires & connectors. I am not the best at cable work, but I'll figure it out.

I'll get the brake fluid issue resolved and start driving this to work again while checking on the state of the new fuse periodically.

 

welcome to honda tech man ^_^

those connections dont look bad
thats a paste that was put in there on day one to make sure the wiring never gets rusty

lets see your sedan

i love those things

 

That's 28 year old dielectric grease, not charring. The connectors / wires in the pictures you posted look fine.