Baffling electrical issue please help

[thatbotguy]

I just got done replacing the high pressure fuel pump on my 88 ranger and now it won't prime. I checked the fuel pump relay on the inside of the passenger fender and was able to make the pumps run by jumping it from the battery, and the relay bench tested good. A multimeter on the plug shows only 1.8 volts across the signal prongs of the plug with the key on, my assumption is that it should be 12. The other relays test at the expected 12 volts. Does anyone have anything idea what could be causing this? I'm stumped, I've checked everything I can think of to check without pulling apart the wiring harness. The computer under the passenger side dash looks fine as well.
Tia

 

[Uncle Gump]

Wait for it....










Does it have fuel in the tank?

 

[Uncle Gump]

Im also confused by your test procedure...

 

[Angry Possum]

If your showing only 1.8 Volts you have a bad ground somewhere, check your ground line(s) thoroughly. The same thing happened on my boat. It read low voltage, turned out it was poorly grounded.

 

[thatbotguy]

Wait for it....










Does it have fuel in the tank?

Yup
Bunch on the ground too

 

[Uncle Gump]

The EEC relay powers the fuel pump relay when the key is turned to run. The ECM grounds the primary coil on the relay for a couple seconds on key up to activate the relay and close the secondary side to power the pump... to prime the system.

Your high pressure pump relies on the low pressure pump to deliver fuel that far. High pressure pump is more of a pusher then a puller pump.

There should also be a fuel reservoir in that two pump system... between the two pumps.

 

[thatbotguy]

Im also confused by your test procedure...

I will take some pictures after work tomorrow, when I don't have to rely on a shitty flashlight.
I didn't explain it super well but everything south of the relay works as expected, as well as the relay itself. Somewhere between the key and the relay there is an issue

 

[Uncle Gump]

Once the ECM sees more then 6 or 700 rpms... the ECM ground the relay coil to run the pumps.

 

[thatbotguy]

The EEC relay powers the fuel pump relay when the key is turned to run. The ECM grounds the primary coil on the relay for a couple seconds on key up to activate the relay and close the secondary side to power the pump... to prime the system.

Your high pressure pump relies on the low pressure pump to deliver fuel that far. High pressure pump is more of a pusher then a puller pump.

There should also be a fuel reservoir in that two pump system... between the two pumps.

I unplugged the high pressure pump and was able to hear the low pressure pump run so they both work. The green relay is the one with the low voltage, is that the eec relay? I'll do some more scientific testing tomorrow

 

[Uncle Gump]

Green is fuel...

 

[Uncle Gump]

And if both pumps are running... it still won't prime the system and fire up?

 

[thatbotguy]

And if both pumps are running... it still won't prime the system and fire up?

I tried jumping the pumps to prime the system and it didn't work, though I think I had one of the spark plugs pulled at the time and I didn't really give it a good try.

 

[Uncle Gump]

Well... take a deep breath

Get your business in order... and let us know.