Hi guys. I just fried my ECU. Truck was running fine. Was backing up to log splitter and got out to check alignment, truck shut off when I was walking back up to cab. No sputter or anything, just like I shut the key off. When I got in I could smell something burnt. After troubleshooting, found that no ground was going to the fuel pump relay, so I pulled the ECU because the ECU provides that ground and kicks it off for pump priming when you don't start it right away. Sure enough, that was the thing that let the smoke out. Opened it up and found a burned capacitor inside.


Question for the forum: Is this something that could happen spontaneously/internally to the ECU, or do I have a short somewhere in the harness?
It's strange to me that if it does have a short, it would happen while the truck was sitting still and idling, which means no wires moving around. I don't want to install another ECU and fry that one too.

88 F150 4.9L 5-speed
The green capacitor in the bottom of the frame is the culprit. One of its legs melted off and it burned right through the other side.

 

The capacitor probably shorted internally, and then quickly died.

Pins 1, 37 and 57 should get battery power with the key on.

 

Oh awesome. That's what I was hoping for. I'll post how it goes tomorrow. Hopefully I don't flush $130 down the drain in about 3 seconds tomorrow when the new ECU comes in

 

Installed the new ECU today and it runs like a champ. Took care of the rough idle and hesitation I could never figure out too. Must have been on the verge for some time now. Regardless, very happy that it's fixed.