Yamaha 150txr intermittent reduction of voltage to fuel pump

[knotworthy]

I have a 2005 F150 that's been giving me quite a bit of trouble all year. Thus far it's been grounds, contacts, clogged injectors, dead fuel pump. It sat for a year last year but we've been running it frequently since January.
Now it's running great but it's doing this weird thing where after shut down it won't restart right away. I checked voltage to fuel pump at the blue plug and it's 2.4v.
Then a few tries later as I'm wiggling wires at the front under the fuel filter it'll kick back on. I don't think these wires are related bc I've unplugged each and they don't have any effect on whether the pump primes when the 2.4v issue is NOT present (if that makes sense).
What can cause this? It's driving me crazy. I don't see any damaged wiring anywhere...but I didn't open the loom.

[boscoe99]

When you say that the motor won't start are you also saying that the fuel pump is not coming on for about five seconds time when the key is turned to the ON position?

By the way, the blue wire to the fuel pump is the ground wire. The red/yellow wire is the 12 volt positive wire. With the key in the ON position you should see 12 plus volts on the red/yellow wire. The ECU will ground the blue wire to cause the pump to run.

The blue wire is only grounded for five seconds when the key is first turned on, when the motor is being cranked or when the motor is actually running. The voltage you are seeing is normal.

What is the serial number of your motor? Your title says it is a 150TXR but in your post you refer to it as a 2005 model year motor which would make it an F150TXRD. Which is it? Has the mod kit to eliminate a hot restart issue been installed if it is an F150TXRD?

[knotworthy]

You're correct it is a TXRD. Edit... See attached image.
The voltage I'm getting is from the red and yellow wire grounding to the block. The pump is not priming when the key is on. I don't know if the hot start issue has been corrected on this motor.

[boscoe99]

You're correct it is a TXRD. Edit... See attached image.
The voltage I'm getting is from the red and yellow wire grounding to the block. The pump is not priming when the key is on. I don't know if the hot start issue has been corrected on this motor.

It is not an F150TXRD. It is an F150TXR. Double check the data plate as the letter D is not used. So, it is not a 2005 model year F150.

The F150TXR came from the factory with the stuff needed to mitigate the hot restart issue.

If you are checking voltage from the red/yellow wire to the block then you have a voltage issue. You should be seeing battery voltage on that wire when the key is on. The fuel injectors also have a red/yellow wire. Check the voltage at the fuel injector connector (red/yellow to ground on the block) and see what it is.

The red/yellow wires run to the fuse block. Check all of the fuses for cleanliness and tightness. Check on both sides of the fuse and see what the voltage is.

Check the connector at the fuse box that supplies battery power to the box. What is it?

[knotworthy]

Thanks I'll check that out. Date of manufacturer is September 2005. I guess that makes it a 2006? This particular motors seems to have a mix of parts from both years though based on what I remember in replacing stuff.

[boscoe99]

Maybe this will help:

[knotworthy]

Very helpful thank you. So there's no resistors or anything at play in delivering power to the pump when key is on, correct?

[boscoe99]

Very helpful thank you. So there's no resistors or anything at play in delivering power to the pump when key is on, correct?

No resistors or other components. But, the power does go through the main relay. That's why I suggested that you check all the way back to the fuse. If low voltage is seen on the power side of the fuse then you will go and inspect the connector/wiring that supplies power to the fuse block.

[knotworthy]

Ok will do. Thanks for your help!

[knotworthy]

Update: turned out to be the main relay. Contacts inside weren't working unless we pressed the relay hard from top. Couple well placed zip ties got us thru the day.
I refuse to pay sixty bucks for a$1 part.
Anyone know the amperage rating of this relay?

[fairdeal]

well, in the diagram above,

if #5 is the main relay, #6 is a 20 amp fuse

[knotworthy]

Ahhhh... Good observation.
The fuse for fuel pump is 30amp.
The other two are 20.
Would the relay need to be able to accommodate combined amperage?

[fairdeal]

The fuse for fuel pump is 30amp.

Hmmm - isn't #6 the fuse for the fuel pump, ecu, injectors, coils etc?

perhaps I am mistaken