Fuel pump wiring

[Scotts96sploder]

I looked, can’t find a good answer.

Problem: 96 5.0, crank no start, can’t hear the fuel pump.

I checked the fuse and swapped relays, checked power at the inertia switch thing, get a spike in run, ran 12v from the battery to the green and both the other (actually tried all the combos) and did not get the fuel pump to run. Checked resistance from there to the pump, all combos mega other than the two not ground wires around 7k. I also had someone crank and poked around at the plug to the pump and got a bunch of different voltages 12/6/5.
Assuming a bad pump but I would like to check power to the pump pigtail to be 100% certain before replacing the whole sending unit. Does anyone know which two pins are the power to the pump at the pump plug?
Once I know it’s the pump I was going to get the whole sending unit, that way I won’t have to go back in there again for hopefully another 25 years.

 

[Scotts96sploder]

So if I go to the plug to the pump and check across blk-Dkg/yel I should see 12 while cranking right?
And if I don’t, i have to assume a broken wire since I already applied 12 to this circuit and got no pump. Actually I guess I didn’t ground the negative, I’ll try that after checking for voltage from the plug.

 

[410Fortune]

Smart
Man
Checking
Voltage at pump
Connector
Before dropping tank

The two largest wires are the + and - for the pump will only get power for a second w key turned (prime)

Next step is to
Send battery power to pump
And see if she fires, how she sounds

 

[J_C]

So if I go to the plug to the pump and check across blk-Dkg/yel I should see 12 while cranking right?
And if I don’t, i have to assume a broken wire since I already applied 12 to this circuit and got no pump. Actually I guess I didn’t ground the negative, I’ll try that after checking for voltage from the plug.

The BK GRN/Yel only goes as far as the inertia shutoff switch, then pink/black out to the pump, so the pink/black wired pin on the connector to the pump, and the black wired pin on the connector for ground, show which two sending unit connector pins to use to try powering it.

 

[Scotts96sploder]

@J_C so just apply 12 to the pigtail on pink/blk and blk, whichever pins match. Will do! I read you could feed back from the inertia switch to do the same thing. But I much prefer at the pump to eliminate wiring problems.
@410Fortune I half dropped the tank looking for the plug before I found it lol. But I read you can change the sender only dropping the back anyway. So if it’s the problem I’m most of the way there.
I’ll probably try that tomorrow after work and get a sender installed Sunday if it’s the problem. I was gonna buy axel parts with this money… ****!

 

[Scotts96sploder]

Ok, ran 12 straight from the battery un-fused lol, to black pink/black. Nothing, silent as the grave. And to be double sure I checked resistance, 1.5M so yeah, I guess the fuel pump just decided to quit all the sudden at the end of a test drive. So weird. You would think it would have shown some kind of symptoms first… whatever, ordering the whole sender now.

 

[Scotts96sploder]

Question, how come mine looks completely different from everything else I’ve seen on here? Also o’Reilly’s doesn’t sell a complete sender, but they have the hanger and pump separately. The pump they sell is not this one… so looks like I’ll have to got both and put them together.
Pump resistance changes from 1.5-50k depending on how much you fiddle with it. Pin out for power testing was correct black-pink/black and no high resistance in those wires. Just in case anyone can use this info.

 

[410Fortune]

That is how the 96 sending units look
You only need to replace the sender if you were having issues with the tank float/ level otherwise it is a waste of money and the factory parts usually work better/
More accurate anyways. Not a bad deal to just replace the pump and strainer
What brand pump did you get?

Precision would be my choice if going to oreillys

 

[Scotts96sploder]

@410Fortune they had the wrong image on the website, the one I ordered was a complete unit from precision. This one appears to have been apart before at some point, some of the plastic tabs/clip things were cracked and the wire to the float was damaged when I pulled it out. I also would like to never have to drop the tank again if I can help it.

So if you’re reading this and think you have a fuel pump problem :
Fuse
Swap relay
Inertia switch
Power check at inertia switch (green/yellow-pink/black)
Resistance check at inertia switch
Resistance check at pump pigtail (pink/black-black)
And to be certain apply 12v to the same pins, and I think you can also apply 12 to the circuit from the inertia switch, but I’m not 100% on that.

 

[J_C]

Yes you can also apply 12V to the inertia switch (at its input to test the switch or its output to leave it out of circuit), but this leaves the variable about whether the wiring to the pump and its ground, and the connectors (contact/corrosion) are good.

 

[Scotts96sploder]

Exactly. In my case I wasn’t sure if I may have nicked a wire installing vinyl flooring, so I had to confirm everything before ordering a pump.

 

[410Fortune]

I always check power from truck and the apply power to pump before dropping the tank

Has saved my from dropping the tank more then once, nice to find out the pump is good and it’s a relay, or bad wiring connection

Well done!