1997 ranger 4.0 where does the power for PCM relay in power distribution box come from?

[wildstang]

1997 ranger 5sp 4L 4x4, Son's truck, he was driving it Saturday, about a mile from our road, power dropped, turned onto our road and stalled. Started then stalled. Got it home, no fuel pressure. Unfortunately from further diagnostics, its not the fuel pump. I can power the relay and pump works. So I have constant power in the #13 leg of the fuel pump relay and pcm relay. I'm not getting key on power to leg 65 on either relay. I also have no spark cranking engine over. I tried putting power to the 65 leg on the pcm relay and the fuel pump will turn on, but still no spark cranking. Where does the key on power come from? Is it directly from the switch, then it turns on relay, then power to the pcm? Or does it go to the pcm, then to the relay then back to the pcm to power up other functions?
Son claimed there was some smoke that came out of the shifter and vents. I don't see how it could up through the shifter because no holes in the rubber boot. Is there something in the dash that the key on power for the power distribution box goes through or the wire routed to? I haven't smelt anything that smelled burnt. I pulled the pcm and no burnt smell with that either.

On the firewall under the booster is 3 big plug ins, does key on power to the power distribution box come through one of those and if so, which and which pin?
Thank you for any help

 

[bobbywalter]

quickest way is to jump to the rf filter on the ign...should be one near the coil.

red light green stripe. that will back door your power. test it first and check for key power... if no key power likely the switch.

 

[wildstang]

I’m not very fluent at electrical. What is the rf filter and what’s it look like? So with key on should be power there?
Thank you

 

[wildstang]

Is it any where in this picture?

 

[bobbywalter]

the single wire grey critter.....red green stripe should be the harness side.

 

[wildstang]

unplug this connector and check for power with key on? I can also add power to this to power the circuit to see if it puts power to the relays and starts?
If the coil pack was failing, would this create a low power and then it fails, this wouldn't prevent the key on power getting to the relays would it? This is great help, thank you very much

 

[wildstang]

bobbywalter excellent advice. I greatly appreciate it. I checked my 95 and had power at the coil plug in then checked the 97 and no power. So I back fed it through the grey connector m, the fuel pump started so I cranked it up and started. Now to find where that wire goes. The wire diagram in the Hayes manual shows a 25amp fuse somewhere. Not sure if that’s it or some short. At worst I’ll put a toggle switch in it.

 

[BobSacamano]

it goes to Fuse 19-25 amp

 

[wildstang]

it goes to Fuse 19-25 amp

Where is this fuse? Is this in the power distribution box? I didn't see any 25amp in there or the fuse box on the side of the dash.

 

[bobbywalter]

there should be an ignition diode in the power distribution box .

and a big fat bastard fuse for the eec computer. maybe fuse 2 i would have to look at it or the diagram....usually a 30 amp

with the base run established by back feeding the rf wire we know that the factory weldments are working and the system functions.

assuming the eec fuse is not blown because you already checked that first... pull the diode and put power to the relay side...if it trips the relays and everything functions then ...check to see if the diode is failed. check the other side for key power.


if there is no key power follow back to ignition switch checking continuity in those wires or the ignition switch to see if anything popped loose.....could be corroded connector or loose connector at firewall ect...


if there is ignition power and it is flowing through diode...


starting with the eec relay carefully inspect the pins and wiring and make sure that the eec relay actually functions...the 85(sometimes 2) needs ground.
and the 86(sometimes 1) is usually tan and black...but tan base color generally.

could be bad relay....or burned ground....or something just popped loose...that ground may be in a connector by the battery ect...came loose...

if fuse is blown or ground is burned then there may be a short or pinched wire for evap or something that will be fun to find...