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.

 

[Curious Hound]

It shouldn't matter whether you use a magnetic relay or electrinic one. They do the same job.

Do you have battery voltage at the relay? One of the contact terminals should have power all the time. One of the "coil" or control terminals should have power when the key is in run or start.

You should be able to use a jumper wire and temporarily jumper across the contact terminals to get power to the ecu. See if that gets you running.

Another thing to check is the ground connection for the relay coil. If the ground connection is loose or dirty, it won't work.