Why does my ignition relay keep blowing?

[1Byounkin]

Truck info. 91 Stock with the older wiring schematic that has the BAP. The Haynes book shows 91 but not the 91 I have. Must of been from the first half.

This morning I had my 91 explorer idling to hookup a trailer. As I was walking to the back of the truck, it shuts off. So I went back to start it. Fuel relay kicks on along with everything else. Turns over. No hit. Spraying starting fluid showed told me that spark wasn't happening. Than used a spark tester. So I checked the +volt at the plug on the coil, with a light tester to ground. One pin should be hot and the rest are ground to the sensors. That I checked the Ignition relay (in the Haynes book it says the EEC relay). Voltage was going to that, but not out putting to coil. So went bought a new relay. The truck started. Ran drove it around the yard. Parked it. Now I start it at ran and started alot easier. Ran for 3 mins than shut off again. So I did the checking at the coil plug again and now no positive voltage from that relay going to it. BUT THE FUSES ARE ALL GOOD. I've seen most post on here where the fuse will blow. So now back at the beginning. You've got to have power to the coil before anything will happen.

Also switched the ICM and the Crank sensor.

Any ideas??

 

[Roadrunner777]

Maybe I need more coffee, but I don't quite understand. Well, here goes...

If you are not getting voltage to the EEC relay:
The path is battery -> Fuse #1 -> Ignition switch --> Diode at #14 --> EEC Relay. If the diode is bad, do not short it or replace it with a fuse. It is there to protect the PCM from voltage spikes. You could swap the diodes. If memory serves, the other is for the 4x4 system but maybe ABS. I'm too far away from the schematics to look it up at the moment. Maybe you can swap the diodes... I once tried to remove one and broke the plastic holder!

If you are getting voltage to the EEC relay:
Sounds like intermittent EEC relay, swap with known good relay.

OR:

You may have an bad ground for the EEC relay.

OR:

The relay socket is getting iffy and gets more iffy with current flow (heat).

 

[BrooklynBay]

Check to see if there's a check engine light when you turn the key. If not, then it's the PCM relay or the connection to the PCM power wiring. The fuel pump can't turn on unless the PCM is providing a ground signal.