Hi there! This is my problem, I got a ford f150 1999 6 cyl 4.2 automatic. My truck starter with a rough idle and when I made a full stop in a red light I had to hit the brakes at all time because it feel like I was hitting the gas and the brakes at the same time, so a friend of mine told me to replace the iac and it work for a couple of days. Then i tried to start the truck and it didn't turn on, I replace the pcv valve, a couple of air hose that was broken, new sparks, clean egr, new air mass flow but the truck didn't start. I check the ignition coil and I have spark on all the 6 cables. The fuel pump relay is good I put another one, so i check the inertia switch i reset the switch and the truck turn on so after that i drove the truck around the neighborhood I was happy truck but the next day the truck didn't want to turn on. After that I replace the fuel pump but the truck didn't start either, So I check the inertia switch and I find out there was no power and I put the test light and the voltage looks real low so I put a direct power cable from the battery to the inertia the truck turn on and when it was on I took it off and the truck turn off. Then I check the fuel pump the fuel pump is not getting power either now I am desperate and don't know what to do. Any help will be very appreciated!!!!

 

In the engine bay look at fuse 10.
If ok swap relay 301 with another relay.
You replaced a lot of hardware before you found the fuel pump issue.
Cost money to guess.
Good luck.

 

Thanks for the reply. I have the diagram on my hands the fuse 10 is empty, and the diagram says not used, and I switched the relay with another and still nothing happens. I also took all the cables from the gas pump to the engine bay and all the cables are good.

 

Fuse #10 in the UNDERHOOD fuse box, not the one in the cab. The manual calls it the power distribution box. That's also where the relay is.

 

I looked in your year's owner manual to get that fuse number so it must be a change.
There has to be a fuse at some other location because the pump has it's own power supplied through the relay.
Now it's voltmeter time to chase it down.
.
Understand when the key goes on and PCM is powered up, the PCM grounds the pump relay only for a few seconds then drops off. The relay supplies power from a separate fused source.
When you crank the motor the relay re-operates when the PCM detects crank rotation from the crank sensor.
Good luck.

 

I am sorry i was confuse with the fuse the other person is right is the one underhood, the fuse in 10 is a fuse 20 and is good.

 

Did you pull the fuse and test it with an ohmmeter?

 

Yes i did pull out the fuse and checked the ohmmeter(with a multimeter) and the fuse is good. But still don't turn on. It's been over 3 months and nothing. Any other advices?

 

I got an update. Check all wire and jump the relay slots power is going to the pump, but there's no ground. Check the slot of ground of the fuel pump relay there's no ground in that slot, can i cut that ground put another cable and ground it to the chasis?

 

You still don't understand how it works.

 

I download the manual, 232 pages but, nothing in there answer my question

 

does anybody knows where is the main relay ford f150 1999 v6 4.2? if it does where is located?

 

.......If your looking for the fuel pump relay, it is shown on page 156 as #301.
.......Page 154 shows you the layout of the relay locations and fuses in that distribution box.
.......Lets review the fuel pump operation;
....Key on powers up the PCM.
....This (the pcm) supplies a 'timed' ground to operate the pump relay to close power from the 'fuse' through the crash sensor to the fuel pump for a pre fuel charge of the fuel rails. The pump has it's own ground source to complete it's circuit.
....Once you begin cranking the motor, the PCM re- operates the fuel pump circuit for full time operation as long as the engine is running.
.....Read this review as many times as you need to get the sequence of operation and relate to the issue for trouble shooting.
.....Note that the PCM never operates outside remote circuits directly, because of the current and control requirements and always uses a slave relay to do the high current supply.
....You have to understand this because we cannot help you beyond this point from a keyboard. You are not missing anything and the manual is all correct on these points.
....You have all you need to test and find the problem area.
....There should be very few instances when you need to alter a circuit to get it to work.
.
If there is still a question, explain exactly what you need to know and we will try again, to help.
Good luck.

 

I got an update. I replace the pcm and check the pressure of gas was too high, so i replace the fuel regulator, now the trucks turns on but now the problem is that every time i turn it on i have to take out the fuel pump relay because if I leave it on the sparks gets flooded.