Need help with pcm wiring
2010 ranger 2wd, manual trans. 4.0l
On the pcm. ( if im not using correct terms i apologize)
but the block on the firewall with the three big plugs with the locks on them. If someone could illustrate for me what wire coming out of one of those plugs turns on the fuel pump relay it would be greatly appreciated. I'm chasing down intermittent power to fuel pump and I'm now suspecting a bad computer

 

The Fuel pump relay gets full time 12volt power with key on, the PCM grounds the relay to activate it but only for 2 seconds, but 2 seconds each time key is turned off and on again
PCM will not ground the fuel pump relay full time until engine is started, RPMs above 400, cranking speed is 200rpm

PCM has 3 connectors two 50 pin and one 70 pin

FR relay ground is on one of the 50-pin(C175B), pin 12 yellow/orange stripe wire



The reason the FP relay doesn't stay on with key on is for safety, if a fuel line should break in an accident the engine would stall(under 400rpm) and pump would shut off, versus continuing to pump out fuel and possibly feed a fire

 

So if the pcm stopped giving the relay a ground while running it would present the issues I'm experiencing no?
Thankyou for the info sir

 

Yes, assuming RPMs are reading above 400

PCM monitors fuel pump 12volt power, its called the Secondary Circuit
P0231 Fuel Pump Secondary Circuit Low
P0232 Fuel Pump Secondary Circuit High
P0233 Fuel Pump Secondary Circuit Intermittent
So computer would set the low or intermittent code if 12v was lost when FP relay is closed(ON)

If also checks to see if the Primary Circuit(the relay coil) has 12v with key on, engine running or not
P0230 Fuel Pump Primary Circuit Malfunction
It would set this code if FP relay coil lost the 12v or if wire to PCM was intermittent while driving

I assume the CEL(check engine light) is not on?
Do you have an OBD2 coder reader?

If you have a code reader then do a "sanity" test on computer
Unplug a sensor, start engine
Should get a CEL and then a code for that unplugged sensor
Repeat with different sensors, but one at a time

There is a inertia switch on the cab side firewall under glove box, it passes the 12v from FP relay to the pump
You can put a test light on it that you can see while driving, and it would go off if 12v was being cut
Looks like this one, has a RED button on the top: https://www.onlinefordpartscatalog.c...tch-7l5z9d362a
If vehicle has ever been in an accident this switch needs to be replaced as once they are "tripped" they can only be temporarily reset

What wouldn't set a code would be bad Ground for fuel pump or bad fuel pump

 

No check engine light but I plugged a reader in the other day from work ( I'm a locksmith, we use it to make keys) and it gave me the fuel pump senondary circut high code.

 

P0232 Fuel Pump Secondary Circuit High
That would come up it you were jumping relay or otherwise feeding fuel pump 12v with key on engine off

You can get a Bluetooth OBD2 reader for under $15(ELM327), that works with any smartphone, APPs are free or $5
And works on any 1996 and up vehicle, so good tool to have

And since there were no:
P0231 Fuel Pump Secondary Circuit Low
P0233 Fuel Pump Secondary Circuit Intermittent
Computer monitor is working
Lack of those Codes means fuel pump has been getting 12v when it should, so most likely you are not on the right track with fuel pump power issue