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1988 Ranger high pressure fuel pump not getting power


MonteroShogun

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Hello, everyone. I need some help. I have a 88 Ford Ranger 2.9L 4x4. The high pressure fuel pump stop working out of the blue. I removed the high pressure pump and tested good. Then I reconnected the high pressure pump and then I found out that the high pressure pump is not getting power. I checked the fuel pump relay with the key OFF and the constant power (yellow cable) is reading 12V, then tested with the key ON and the constant power wire (yellow in my truck) and the ignition switch wires are reading 5-6V. Is there a chance that if the low pressure fuel pump went bad, that is causing the reading of 5V in the relay connector when the key is ON (I don't think so, but needed to ask) or... is there a chance that the PCM went bad ? Does the low pressure fuel pump (in the tank) is the one that makes noise when turn the key ON or is it the high pressure fuel pump the one that makes noise? Any help, suggestion will be really appreciated. Thanks in advance!
 


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RonD

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Welcome to TRS :)

The computer only turns on the fuel pump relay for 2 seconds with Key ON, after that you will see 5-8volts on the fuel pump wires, until engine starts or key is turned OFF
There is no amps, its just 5-8v from the computer's Monitor circuit to see if fuel pump relay is working, so very normal to see that with key on after 2 seconds

Ford spliced in the high pressure pump power to the in tank pump's 12volt wire under the truck near the high pressure pump
And this splice is known to corrode and fail
So follow the high pressure pump wires to this splice, cut and re-splice as needed
And make sure pump's ground wire is also good, there is no 12volts unless there is also 0volts(battery ground)
 

MonteroShogun

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RonD.

Thank you very much for the prompt reply. Would you happen to know which of the two pumps is the one that can be heard when turn the key ON? the low pressure pump in the tank or the high pressure pump? Thanks again!
 

Uncle Gump

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I believe they both come on...

Per RonD the fuel pump wire is spliced to "both pumps".
 

RonD

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+1 ^^^

Both pumps should come on for the 2 seconds


You can turn on the pumps 12volt manually, by turning on the fuel pump relay
You will need to find your OBD1 connector in the engine bay, should be passenger side inner fender, between relays and firewall

Look here: https://www.therangerstation.com/tech_library/OBD_I.shtml

OBD1 connector is shown and the Fuel Pump slot is labelled
That slot is the GROUND that turns on the Fuel Pump Relay, same ground the computer uses

Make a jumper wire from Ground(or battery negative) and put it into that slot
Turn on the key and fuel pump relay will close and STAY CLOSED until key is off or jumper is pulled out

This can make troubleshooting easier with dual pump set up, you can "feel" if high pressure pump is on
 

fyre82

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I've been struggling with a similar intermittent no fuel problem in my 88, most recently twice with higher temp, 210 and AC on. It died like it was out of fuel, pump ran at key on and gave me spurts of fuel and air at the schrader. It wouldn't start until it cooled below 190, after the flatbed ride and a tow strap ride home. I'm looking at all of the above to try to work this out, plus flushing cooling etc.
Thought in my head, could the fuel pump relay fail due to heat, or am I looking at a vapor lock? haven't heard about that in forever. I replaced the tank pump last year as it failed completely.

Thanks Ron for the OBD fuel pump hack, I will be installing a jumper for if/when it happens again.
 

RonD

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Vapor Lock was an issue when engines use mechanical fuel pumps and the fuel pressure in the fuel line from gas tank to pump was 0psi
So on a hot day a metal fuel line near exhaust pipe could get hot enough for gasoline to vaporize, and mechanical fuel pump can pump "air/vapor", so engine would stall
Or after shutting off the engine and letting it sit for a few minutes the fuel line would get heat soaked so vaporized fuel

With fuel injection pressure is 30psi so fuel can't vaporize in the fuel lines, which is why you haven't heard of this is a long time.

Its why there is pressure in you cooling system as well
Water will boil at 212degF(sea level)
50/50 coolant/water mix will boil at 225degF
Add a 15psi rad cap and 50/50 boils at 260degF

Gasoline is much the same, at 30psi it wouldn't "boil" unless it was on fire, lol
 


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