Explorer Fuel Issues (Won't Start)

[tb258]

Fuel Issues (Won't Start) 12/2

Well, on Thanksgiving Morning the '95 Explorer would not start. We could not hear the fuel pump click on. So, after having to stay at home for the holiday and reading through these forums I figured the first thing to do was replace the Fuel Pump Relay. I have no distribution box diagram (if anyone could scan it, it would be much appreciated) so we just replaced one of them and it evidently was the right one as the Ex fired right up. It ran great for 3 days. Monday morning, it would not start again, same symptoms. I got 2 more new relays and this time it would not start. We have checked all the fuses in the distro box and tried replacing all the relays. We checked to see if power was coming into the fuel pump shutoff (inertia switch) and no power was coming from the front. Does anyone have any ideas? I'm pulling my hair out over here. Sorry for the long winded post, and thanks in advance for any help.

Tom

 

[Opera House]

Fuel pump 101

The current flow is: battery, fuse, relay, inertia switch, tank electrical connector, pump, back through the tank electrical connector, and ground. Look for signs of heating discoloration on ALL fuses and relays. Many have the power jumpered to another component and heating results in a bad crimp connection. Corrosion can initially cause this from salt in the air.

Relays get warm because they normally dissipate about 5-7 watts of power. Won't heat your house but it should feel warm to the touch. Remember the fuel relay is on all the time the engine runs. If the vehicle won't start, it won't get warm.

When you first turn the key on, the relay turns on for about 5 seconds then shuts off until the engine starts. This makes it hard to diagnose what is happening.

The computer shorts one side of the relay coil to ground. The other side of the coil goes to the switched 12V power.

The relay coil operates a switch inside the relay package. A box figure on the relay indicates the coil. The other two pins of the relay are the switched contact. If you jumper those two pins, the pump should operate if the key is on or not.

If this doesn't make it run, you keep going down the circuit till you find a bad connection where the voltage stops. Normal pump current is about 5 amps. You can measure this by replacing the fuse with a meter. Many wire crimp terminal pins will fit in a fuse or relay socket and allow connection to a meter. Under 3 amps the engine will perform poorly or stop. Resistance in connections will cause lower currents and lower voltage at the pump. The pump can work on as little as 6 volts and the engine will run.

Switching the relay has a chance of making it work. If you have switched it a few times, are you sure you have switched the correct relay? It could also be the ECM relay that powers the computer. No computer power, no pump.

 

[tb258]

Thanks for the reply, Opera House. One quick question, the ECM relay you speak of. Is that one of the 3 relays in the Distro Box, or is that located somewhere else? We've switched all of the relays around in the distro box, and had no success. And another question is, is there a difference between those 3 relays or are they the same type of relay? I'm going to use your advice about using the jumper to get the pump to run today. Thanks once again.

Tom

 

[Opera House]

Relays are generally interchangable

If they fit, they will handle the current. 5 pin relays can replace 4 pin relays but not the other way. Do a search for online manuals. I was able to download an Adobe format one for my 97.