I have an '88 f-150 with a 4.9L I6. Yesterday I was backing out of a friends driveway and the truck shut off on its own. it started right back up and sputtered once on the ride home. So I checked codes and got

41- no exhaust gas oxygen switching detected always indicating lean.
25- knock sensor not detected during dynamic response koer.

Now it won't even pre-pump the fuel when the key is turned on and i checked the pump and its good. I don't think its pumping while I try to start it either.

Is there a fuse that I missed or a relay that someone knows about that can cause the fuel pump to not get power.

 

turn the key on and see if the relay clicks if it doesn't then thats the problem

 

i don't know where the relay would be to check that

 

Don't know about your 88, but on my 90, the relay is on the drivers side inner fender. It is in a plastic box next to the air filter housing. There are two relays. One is for the ECC, the other for the fuel pump. Have someone turn the ignition on and off while you hold the relays in your hand. They should both click when they turn on, and 2 seconds latter the fuel pump relay should click again as it turns off.
Another thing you can check is the inertia switch. This switch shuts off the pump if the truck is in an accident or rolls over. Both the relay and the switch are generally reliable, but you need to start somewhere to chase down this problem.
How did you test the pump to know it is good?
I don't think the 300 has a knock sensor. After you solve the fuel problem, try unhooking the battery for 10 minutes then reconnect and drive it for a few minutes and pull the codes again.
Good Luck Frank

 

the fuel pump relay wasn't working so I changed it and still nothing how do I reset the inertia switch

 

I found the switch and the red button was already down. I bypassed the switch and still nothing so I plugged that back up and I'm still getting no fuel pump power

 

you actually have 2 fuel pumps.

 

Ya a low pressure in the tank and a high pressure in line neither are doing anything but I don't think the tank pump kicks on till the truck is turned over and the sound of it is so quiet that i wouldn't be able to tell if it is running anyway

 

"the fuel pump relay wasn't working so I changed it and still nothing"
Nothing as in the relay still doesn't work, or the relay works and the pump doesn't?
Is the ECC relay clicking on and off when the ignition is turned on and off?
If it is, you may have a damaged wire going to the fuel pump relay, or corrosion in the relay socket.
Good luck Frank

 

the relay is brand new but its not kicking on so there must not be power going to the electrode that kicks it on and off and the ECC is working fine.

 

If you know where the wires run please let me know i traced the positive from the pump back up to the relay thats how i found the relay. but where do the wires come from if someone has a diagram it would be much appreciated

 

The eec relayturns on the fuelpump in a sence, does the check engine lite come on when the key is on run? If the light is on the u have power to ecm and the next step is to check the connections at the relay and also the neg terminal at battery. The neg wire has been known to corrode and cause trouble also

 

the check engine light does come on and which negative wire is known to corrode

 

I had this problem a few days ago. The negative wire runs along the top (or somewhere around there) of the radiator and connects to the negative terminal on the battery, make sure it's grounded well.

 

I'm going get a new battery and fuel pump just to take them out of the problem