You're chasing your tail here. The pump should have 12v to it. Disconnect the harness from the pump and check for voltage. Then reconnect the pump and check for voltage. Let us know what you find.

 

You're right, I am, but I'm learning.

"You won't do that again, will ya?!"

So today the pump assembly was rebuilt and so far it's working as it should. Didn't have time to test anything thoroughly today, but I'll still test the harness and pump volume test soon.

 

How can I measure the pressure on my pump? I have the same problem with my truck.

 

You can't very easy.
Test fuel pressure at the injector rail on a fiitting made to connect a gage to. It looks like a tire stem.
Normally the pressure should be around 35 psi +/- after the regulator drops it down for injector use.
Good luck.

 

Is it the one in the left rail with a cap?

 

It's the ONLY one on the fuel rail.

 

Can I use a regular tire pressure gauge to measure the pressure at the fuel rail port?

 

It might work if you can screw the cap onto the fitting and is will seal..
You don't want any gas flying around the engine bay when the motor is running or hot. That's a no no.
DON'T do it like checking tire pressure, use a gage meant for the use.

 

Hi Guys, I need a little help here. My newly aquired 99 F150 with the 4.2 V6 engine has a crank-no-start condition. I'm getting battery voltage at terminals 30 and 86 of the fuel pump relay. Terminal 87 of the relay has 6.8 volts and same is present at the green wire on the fuel cutoff switch located at the right kick panel. Terminal 85 has ground. Voltage is even lower at the fuel pump connector, a mere 4.5 volts with the ignition ON. It does go up to battery voltage for a split second when I turn the ignition switch to the off position. Original fuel pump was shorted out, I'm in the process of replacing it along with the rusty fuel tank. I notice that this thread has been inactive for 2 years and I'm trying to resucitate it because it is very similar to what I'm dealing with.

 

The very first check to make is with a pressure gage on the fuel rail test port.
Key to run powers the computer that in tern starts a 3 second timer that puts out a ground to the pump 'relay'.
A the end of the timing, the relay drops.
Do this several times to get a look at pump performance.
If you do not see the pressure build to about 35 psi in three or four key cycles, there can be a pump or circuit issue.
.
At cranking, the computer is already powered up.
That being the case, the crank rotation is sensed by the computer and re operates the timer circuit full time as long as the crank is rotating and computer is seeing the crank position sensor pulse train.
This keeps ground on the pump relay operating the pump full time.
Do this and not chase voltages unless there is a total failure of the pump to turn on with the key to 'run' for a few seconds and or low or no pressure.
Good luck.

 

Voltage readings for the fuel pump are valid for ONLY 2-3 SECONDS WHEN THE KEY IS FIRST TURNED TO RUN.

Readings taken at any other time, unless the engine is running, are INVALID.

 

Thanks for coming to the rescue Bluegrass. Fuel pressure at the rail is zero. Pump does not start. Grounds to the fuel pump connector, checked with a wire directly to the positive pole of the battery check at battery voltage. Positive wire at the fuel pump connector is 4.5 without the direct wire and 6.6 volts using the direct wire (this time hooked to the negative side of the battery). Similar readings are seen at the fuel cutoff switch green wire, with or without the relay 301 connected. The terminal 87 of the relay 301 reads 6.78 volts regardless of the position of the ignition switch. I think that terminal 87 should not have any voltage when the relay is not connected. This 87 relay terminal may be getting the 6.78 volts from another wire somewhere at its way towards the fuel cutoff switch. Please correct me as necessary.

 

Meanwhile, terminals 30 and 86 of the relay 301 read battery voltage with the ignition ON.

 

Thanks Projects. Voltage in the first 2-3 seconds after the ignition is turned on is 4.5 volts at the fuel pump connector. A known good fuel pump does not turn on during that time.

 

I also noticed that when the ignition is turned on, the speedometer gauge goes to its limit, then goes back to zero. Is this normal?