Fuel Pump stopped working, Electrical problem.

[jmullins09]

Hey guys. I'm at my wits end.

Truck:
1994 Ford Ranger XLT V6 4.0L (non cali)

My Issues:

The truck died on me one day, I drove it a couple miles and parked, couple of hours later I tried to start it, it started for 2 seconds than choked out and died. Would not start again.

First thing I did was check the fuses, they all seem to be in working order. I checked to see if the inertia switch was popped, it was still pressed down. Had it towed to my house.

What I've done so far:
Replaced the old fuel pump with a new one, replaced the fuel filter, replaced one of the relays (specifically the fuel pump relay while the old fuel pump was still in) Checked the wired for voltage at the connector end, checked for voltage going to the engine fuse box, to the inertia switch, to the connectors that connect the inertia switch, pink/black wire to fuel pump, and red/yellow wire.

For some reason, the fuel pump will run bare from battery to pump at 12.6v, it will run down to where it should be if I short from the battery and bypass the inertia switch. But whats weird is that from the fuse box, I'm getting 12V into the box and 5.5V coming out going to the inertia switch. I don't know why the drop in voltage, is the PCM bad or is it a relay? Any help would be extremly appreciated, I need this truck and I cannot afford a new vehicle.

 

[Earl43P]

Welcome to The Ranger Station!

You will only see the 12v out of the relay for 3 seconds after the key is turned to Run OR all the time while the starter is cranking it over.

I would try a new relay since they are a common failure item. You should also know that the PCM relay supplies the power to the fuel pump relay.

When you turn the key to Run does the Check Engine light come on? (this is a test of the CEL lamp AND an indication that the PCM relay is operating). If not, replace the PCM relay.

You should also know that the fuel pump's GROUND is located all the forward on the inner fender. You might want to clean up your ground points.

This diagram might explain things better than words: http://www.therangerstation.com/tech_library/EDiagrams/files/Diagram_Enginecontrols4_0_3_0_1of3.JPG

 

[jmullins09]

Replaced the relays but I don't know if I replaced the right one for the PCM. But I bought 2 relays and stuck the one for the fuel pump in and one in the EEC.

 

[fh in Houston]

Change the PCM

I have the exact year and engine ranger. About three months ago, I had the same problem. Car stalled would not restart, etc. Changed fuel pump, would not work. Finally checked voltages and got the same readings as you. Tested direct power to the pump and worked (new and old).

Found out that the PCM (POWER CONTROL MODULE), which is the system computer, would be the culprit because of the odd voltage readings. It is about $100 at the local parts. It could be listed as PCM or ECM (Engine Control Module). On our model, the PCM is in the drivers side fender/firewall, and is difficult access. I had to remove the fender wheel cover/cowl to get to one of the bolts. It is a simple job (unplug wiring, remove, install, plug in wiring), just hard to get to.

I recall the ranger misfiring before it stalled, which sent me along the track of the fuel pump to begin with.

I am 100% sure this is your problem.

Happy mechanicing.

 

[jmullins09]

Got the PCM out, to make it clear its a big square metal box correct? People where not joking when they say it is a pain to get to. Going to get a new one today, by god I pray this is the solution.

 

[alwaysFlOoReD]

It is a big square metal box ~ 2"x 6"x 8" with a [iirc] 104 pin connector.
Good luck,

Richard

 

[jmullins09]

That was it. She pures like a lion now. Can someone sticky this or make it a priority so someone else who has these exact problems doesn't go through the things FH and I had to endure. Some tips for others, The PCM (or EEC or ECM) was located on the drivers side deep in there right above the wheel fender. it has a black rubber housing on the front of it. If you follow the main wires from the engine fuse box down you'll run right into it.

 

[MichaelWingley]

I'm having this exact problem right now. About 13 days ago, i changed the fuel pump 2 days later, and then the next day about halfway through the day it just stopped running. It continued to crank, but wouldn't start, i know it's a fuel problem because when i attempt to test the fuel pressure it says i have 0. So i tested the Fuel pump relay and i have 68 ohms going through that, (Google says its supposed to have 60-80 ohms), Then i tested the fuse box and it had 10.35 V, then i went down to the fuel pump inertia switch, and it read about 9.63. The fuel pump read the same. Not exactly the same readings but still lower then normal. IDK if your going to sea this, but if you do id appreciate any help and/or your opinon if you think its the ECM.