ECU relay failures

[j-driver]

I've got an '87 XLT (2wd) that I seem to be unable to get a working ECU relay for. The truck was running before the original relay failed. I ordered two on ebay, carquest surplus stuff, and both turned out to be bad. So this time I ordered the SMP RY-111 on Amazon, looks the same, and it seems to be nonworking as well. I tested one of the carquest relays before installing it, making sure I had the polarity right (positive on the center small terminal, #2) and it was bad right out of the box. I even went to the extent of hacking a GM relay to get power to the ECU, first without, then with a flyback diode, which worked at first but I think I had a cold solder joint in the hack that I did.

Two questions. First, the stock relay is said to be "electronic". I took the cap off one of the Carquest relays, and sure enough, there's a very small component board inside that controls the trigger coil. Based on my very limited knowledge of electronics, it looks like they use a small transistor to drive the relay coil, an RC circuit to give it a soft start, and a flyback diode to suprress the voltage spike when it shuts off. So does anyone know if all the bells and whistles on this relay are really necessary, or can I get by with wiring in a different relay with a flyback diode and not burn up the ECU? I'm getting tired of going through the same loop again and again.

Second, is it possible there's a problem somewhere that's causing the control boards to fail? If so, how would I troubleshoot it? I'm reasonably sure that at least one or two of the relays I bought were bad right out of the box.

I'm curious whether anyone else has had a similar experience. Seems trivial, but the truck won't run without some way of getting power to the ECU. Appreciate any help or feedback.

 

[PetroleumJunkie412]

Way above my pay grade.


Where's @RonD when you need him...

 

[Curious Hound]

I'll give this some thought in the morning. Which terminal is #2? Most times, automotive relay terminals are labeled 30, 87, 87a, 85, 86. 87a, in the center us rarely used because it is the "normally closed" contact.

 

[j-driver]

Thanks, the GM relays are almost all like that and maybe the newer Fords are too, but I haven't worked on anything newer than what I've got. Those relays usually have a pinout stamped on the top so you know what's in them. This one has just 4 terminals, two large ones -- one from the battery via a fusible link, and the output to the ECU, and two small ones, one that takes 12v from the ignition switch, and one to ground.