No power to fuel pump

[CountryBoy704]

Just recently completed an m5od swap ('97m5 for '87a4ld) and trying to get the ol girl to crank up. The pump is not cutting on with the key in run position. I've replaced the fuel pump and eec relays, bypassed the inertia switch, checked and cleaned the connections at the pump. The pump runs if you apply 12v at the inertia switch wires. Any ideas?

 

[CountryBoy704]

Anybody? I'm lost and trying to figure this out

 

[Lil-Pony]

Check fuses and check for power at the fuel pump relay.

 

[doorgunner]

Get a good wiring diagram...check all fuses..make sure that the correct wire going to the bulkhead connection has good voltage......then make sure the wiregoing from the bulkhead connector to the EEC relay has good voltage....then make sure that the wire going to the fuel pump relay has good voltage....then make sure good voltage is going into the inertia switch has good voltage 12-13 volts....then make sure good voltage is coming outta the inertia switch----since you know that the wiring is good below the inertia switch to the fuel pump.

 

[RonD]

The EEC relay supplies the Fuel Pump Relay 12v to open and close, computer supplies the Ground to open and close the fuel pump relay.

The fuel pump's actual 12v power, that passes through the fuel pump relay, is from a 30amp fuse in the engine compartment fuse box.

So the EEC relay supplies relay power not fuel pump power

Fuel Pump power is like this:
30amp fuse--------(Fuel Pump Relay)-------Inertia switch--------Fuel Pump(s)

Fuel Pump Relay power is like this:
EEC Relay------Fuel Pump relay------PCM(computer)--ground

 

[Earl43P]

Wiring schematic link:

http://www.therangerstation.com/tech_library/EDiagrams/files/Diagrams_ElectronciEngControls2_9_1of3.JPG


Check the ground near the PCM and at the radiator support.
There may be a small ground from B- that came loose.

If 87 has a Check Engine Light, it should come on in the Run position indicating that the EEC relay has energized. The fuel pump relay coil gets its power from that happeneing, as Ron described.

 

[CountryBoy704]

thanks for the replies! So the pump works if I jump power to the pin on the fuel relay and I am geting 12v in from the starter relay so I believe one of the other two wires is the culprit. They both run into the harness back towards the ecm, one should be a ground into the ecm and I'm not sure about the other one? this is a 1st/2nd gen so no engine compartment fuses here

 

[RonD]

Fuel Pump relay should have 4 connections
The 2 load connections, passes power thru when relay is closed
And 2 for relay power and ground.

The relay power will be 12v but only when key is on.
The relay ground will be a ground for 2 seconds when key is first turned on, so you can hookup a test light to 12v and to this slot and cycle key on and off to see which slot is the ECM ground

The Load 12v power will have power all the time, key off or on, and it will have a fuse somewhere.

OK found an 1987 wiring diagram
The fuel pump power is fused with a fusible link, 20ga blue, EEC relay also uses a 20ga blue fusible link, they are connected together, at the battery or solenoid battery side.

That fusible link will be on a Yellow wire going to the fuel pump relay.(EEC relay also uses a Yellow wire).
Wire to inertia switch will be Orange/light Blue
Wire for relay power will be Red, it gets this power from the EEC relay, so only when key is on.
Ground from ECM is Tan/light Green.

So Relay wires should be
Yellow-----to battery via fuse or fusible link, 12v power 24/7
Orange/light Blue-----to inertia switch, and then fuel pumps

Red----to EEC relay, fuel pump relay power, 12v only when key is on
Tan/light Green----to ECM, grounded to turn on fuel pump

If fusible link is bad or missing use in-line 30amp fuse to replace

 

[Gilbee01]

Ron if the inertia switch is bad couldn't that also cause the loss of power?


-gil-

 

[RonD]

Ron if the inertia switch is bad couldn't that also cause the loss of power?


-gil-

Yes, but he added power at fuel pump relay and pumps came on so inertia switch is passing power as it should.

 

[CountryBoy704]

back at this today, inertia switch is bypassed just in case, I have continuity through all fusible links and power going into the relays, going to go check the computer ground per RonD's suggestion now thanks for all this help!

 

[CountryBoy704]

ok so if I ground the ecm wire from the fuel relay directly the pump cuts on regardless of key position, starting to wonder if the ecm is bad?

edit: my multimeter reads 12v at both the ground and power wires for the fuel relay with the meter ground on the battery and key both on and off, not sure if I'm testing incorrectly or if that means something else is wrong?
Also remember I just finished an auto to manual tranny swap so is there anything from the wires that do the neutral safety switch or reverse sensor that could play into this?

 

[RonD]

Yes, it would read 12v on both relay power pins, but only with key ON.
The relay part is just 1 wire wound around a metal core, when it has power flowing thru that 1 wire it turns metal core into an electro-magnet, that will pull the contacts closed, the Load part of the relay.

All mechanical relays work this way, so do fuel injectors.

So if there is 12v on one end of the relay wire there would be 12v at the other end, but no power flowing, you need a ground at one end to get flow.

Check the EEC relay, that's what provides the 12v to the Fuel pump relay, with EEC(key) off there should be no power at the relay pins, so grounding relay wouldn't turn it on, it reads like it has 12v 24/7, which is not right.
Power would be on the Load pin 24/7, that's direct from the battery as it should be.

Pull out EEC relay, that should cut power to Fuel Pump relay, if it doesn't then some one has rewired it, wrong.

The 4 pins in Fuel Pump relay
Relay part
1. 12v from EEC relay to Fuel pump relay, only on when EEC relay is on, and EEC relay is only on when key is on
2. Ground from ECM, this pin would show 12v, if above has 12v and ECM is not grounding it at the time of the test.

Load part, clicks closed when relay part has power flowing thru it, so relay has 12v and a ground
3. 12v from fusible link to battery, 12v all the time, not on key switch
4. Power to inertia switch when contacts close

 

[kimcrwbr1]

There is a fuse link from the battery to the fuel pump relay hot all the time.
with the key on you should get hot from the eec relay to the fuel pump relay coil
the computer controls ground to the fuel pump relay coil.
You can try running the fuel pump full time by jumping the the EEC test connector I will get you the link.

 

[kimcrwbr1]

http://www.therangerstation.com/tech_library/OBD_I.html
Scrool down to the analog voltmeter method just below that it shows you the fuel pump pin on the VIP connector. Run a jumper wire from it and turn the key on and then touch the jumper to ground the fuel pump should run. You can test the fuel pressure without running the motor that way also. If the fuel pump runs then it is the ground wire from the computer to the relay.