Truck Died!!

[BillupsOMally]

I was driving, the truck stalled, then bump started itself back to life right away, (It's a standard), drove a few seconds, then did it again, and kept going like that until I pulled off the highway and coasted into a parking lot. A few of the times it stalled it took a few seconds to fire back up again, if I gave it any throttle it sounded like it was backfiring out the intake.

Soon as I stopped I popped the hood and saw smoke coming from a relay near the fender/firewall on passenger side, so I popped off the battery cable and disconnected the relay. It was almost too hot to touch!

It's not the fuel pump relay. What IS the relay for, and any ideas why it would do this?

1989, 2.9L, 2WD, Ranger

 

[AllanD]

Backfiring?

On a 2.9 that's a classic clogged fuel filter symptom.

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[BillupsOMally]

That would explain the backfiring out the intake, but what about the relay melting down like that? From my wiring diagram I'm thinking it's the EEC Relay that melted down, and if it was intermittently connecting then breaking the circuit, which I think would turn off power to the ECA, which would turn off the fuel pump, which would cause the dying and backfiring?

Is that even possible, or am I just stupid? lol

 

[AllanD]

I didn't see that part when posting...

The two relays are EEC power and fuel pump relay if the Fuel pump relay
is intermittent that would cut off the fuel supply and generate identical symptoms...

As for why the relay burned up?

Old age? is it "hanging" by it's wires?

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[BillupsOMally]

OK. So I checked the EEC and Fuel Pump Relays. The EEC Relay was fried, and the Fuel Pump relay clicks really fast when you energize it.

Replaced both.

I put a fuel pressure tester on, fuel pressure was 40 psi, until I started turning it over, then it would quickly drop and hover around 15.
Replaced the fuel filter and retested, came up to 40 psi again, and only dropped to 35 or so once I started cranking.

The distributor cap was corroded quite badly (only 2 months old), replaced the cap, rotor, wires, and plugs. (Plugs were fouled black.)

Cleaned connections to the ignition coil and checked for spark at the coil.

When it first starts turning over it sparks quickly, like it's supposed to, then quickly slows down and then stops sparking altogether, and occasionally fires after that.

I tested the primary coil and secondary coil resistances, and they tested comfortably within the spec range.

I tested the resistance of the energizing circuit on the new EEC relay and the burnt one, the new one had a resistance of 8 ohms or so, and the burnt one was a direct connection (.01 ohms).
According to my wiring diagram the red wire (which is the negative side of the energizing circuit on the EEC Relay) supplies power to multiple sensors and 2 pins on the computer. Is it possible that when the relay fused, the extra amperage from the reduced overall resistance of the circuit damaged sensors or possibly even the computer??