1999 f-250 super duty... okay, here is what i have going on. basically no power to the fuel pump. For the last 2 weeks the fuel pump relay and 1 of the relays behind the radio (next to the blue relay) would chatter and the truck would die. Wait about 5 minutes and turn the key on and if the chatter was gone then it would fire up and run... So NOW no chatter on either relay and not cranking up. - motor turns over just fine- just no power to fuel pump. So i changed out the relay- both behind the radio and the one under the hood. still chatters and no start. i have checked the Inertia switch and 12 volts there...
Here is my question, when i turn the ignition on, i have no power to the base of the Fuel Pump Relay.... Where does the power come from to power the relay???

 

actually under the hood in the fuse/relay box, i can remove the fuel pump relay and i do have 1.2 volts on one of the holes that the relay plugs into... all others are dead.

 

and it is a 5.4L

 

Not sure about your model but in many applications the fuel pump relay gets its power from the ECU relay. No power to fuel pump can be either a bad ECU or pump relay.

 

ya i think i need to find out why there is no power to the relay base with the key on.

 

Remember, the fuel pump will only work for a few seconds in the key starting position. After that, the ecu has to detect engine movement/running to then supply power to the fuel pump relay to keep the engine running.
If you just turn the key to the run position, you won't find any power supplied though the fuel pump relay.
A safety feature.

 

ah ok that makes sense... so right now when i turn the key to the on position, the new relay behind the radio and a relay under the hood "new too" in the fuse box buzzes.. if i turn it off and on or wait 10-15 minutes the buzzing will stop and it will start... i removed all the grounds under the hood and under the dash that i could find and cleaned them and still the relays just "chatter" like crazy... at his point i think i am going to figure out how to put 12 volts to the fuel pump side of the inertia switch to see if the pump will run so i can fire it up..

 

Remove the kick panel covers and inspect the ground studs and lugs for corrosion or looseness.

There are also two grounding points on the firewall under the hood, tucked back into the corner behind the fuse box on the driver's side. They're critical for proper operation of the PCM (which controls so much else including the fuel pump relay).

 

I have cleaned both ground studs under the hood near the fuse panel. Also took off and cleaned the ones under the dash. actually did that a few days ago.

So as of now, i do have 12v to the Inertia switch. I jumped the switch out and the fuel pump did not run. Turned Key on and no pressure out of the schrader valve in the fuel rail, just dead.

So i will pull the bed off the truck this afternoon and check the fuel pump for 12v's.

I just didnt think the fuel pump going bad would cause the relay to "chatter".

 

There are also grounds behind the kick panels. Check them.

It won't (can't). That's something else besides the pump.

 

Sorry i forgot to mention that i did get the ground behind the kick panel.
Well here we go with the update. So when i put the key in and turn it "on" the chatter is gone from the fuel pump relay and one relay under the hood in the distribution box. So no more chatter . Here is what i have now:
1. I have checked/cleaned (wire wheel/sandpaper) all the grounds i can find.
2. cleaned battery terminals.
3. charged the battery over night to make sure its hot.
4. cleaned the 12v stud on the distribution panel under the hood. 1/2 nut with big cable hot 12v.
5. verified with key in on position that there is 12v at the Inertia switch.

At this point try to start. Turns over but no starting up and running.
Got out can of ether. few shots in the intake hose and kicks off and runs then dies.

Turned ignition back on. hit schrader valve, no gas or pressure.

SO i think hmmm fuel pump... still thinking fuel pump actually...

SO HERE is where i have an issue..... key is off and my dad says - hey lets hook the OBD2 up to it and see if there is a code?? We did this yesterday and nothing... BUT this time it shows Cannot Connect ????

 

You cannot communicate with the truck with the key off. The ignition has to be in the RUN position, otherwise the computer is turned off (not powered).

 

sorry had a typo. i had the key on and it would not communicate. tried several times and "unable to establish a link with the vehicle" or something to that effect is what i got each time.

 

i actually read this post https://www.ford-trucks.com/forums/5...y-chatter.html and it sounded exactlt like my issue.

I wonder if the ECM went out based on the fact that the OBD will not lync to it.