1984 won't start

[jay]

Hi folks

any help would be appreciated as mentioned above I have an 84 I replaced the fuel pump and filter and, the vehicle starts if I place a jumper in the fuel pump relay and I can remove the jumper and it stays running, I know on start up on the fuel pump relay should have 12v for around 2 seconds on one of the wires, and it does get voltage but it only around 2-3 volts that read on the meter. now maybe this is related and maybe its not but the cooling fan also quit working now I know the cooling fan is a stand alone from the ECM on the 84 so maybe I am looking at a possible ground issue

Thanks for your time

 

[ecss]

Hi folks

any help would be appreciated as mentioned above I have an 84 I replaced the fuel pump and filter and, the vehicle starts if I place a jumper in the fuel pump relay and I can remove the jumper and it stays running, I know on start up on the fuel pump relay should have 12v for around 2 seconds on one of the wires, and it does get voltage but it only around 2-3 volts that read on the meter. now maybe this is related and maybe its not but the cooling fan also quit working now I know the cooling fan is a stand alone from the ECM on the 84 so maybe I am looking at a possible ground issue

Thanks for your time

Did you apply 12 volts to pin G of the diagnostic connector?
Then you removed the wire and the engine started?

Which colored wire only had 2 to 3 volts?

When the oil pressure reaches 4psi the oil pressure switch will close and supply the fuel pump relay with
12 volts to the fuel pump fuse.

These are the schematics for the 84 that I have.

First schematic shows the cooling fan.
Do you know where the cooling fan relay is?
If you do verify you have 12 volts on the large Red wire.

Second schematic shows the fuel Pump circuit.

Third picture shows the Battery fusible links. Probably one of them is blown.

 

[jay]

Hi apprciate the response

I jumped the fuel pump relay out like was told to try in another form and it started right up and then I pulled it out and it kept running..........is the connector you speaking of inside the cab of the vehicle? I believe it is E the color Black and yellow line I believe is to prime the throttle body but it only give me 2-3 volts not 12 to prime fuel pump




u removed the wire and the engine started? yes

colored wire only had 2 to 3 volts?

n the oil pressure reaches 4psi the oil pressure switch will close and supply the fuel pump relay with
12 volts to the fuel pump fuse.

These are the schematics for the 84 that I have.

First schematic shows the cooling fan.
Do you know where the cooling fan relay is?
If you do verify you have 12 volts on the large Red wire.

Second schematic shows the fuel Pump circuit.

Third picture shows the Battery fusible links. Probably one of them is blown.







[/QUOTE]

 

[ecss]

I jumped the fuel pump relay out like was told to try in another form and it started right up and then I pulled it out and it kept running..........is the connector you speaking of inside the cab of the vehicle? I believe it is E the color Black and yellow line I believe is to prime the throttle body but it only give me 2-3 volts not 12 to prime fuel pump

There are 3 ways to power the fuel pump.

1)Jump 12 volts to pin G of the diagnostic connector.

2) When engine oil pressure reaches 4 psi the oil pressure switch closes which applies 12 volts from a fusible
link to the fuel pump motor. (This is backup in case the fuel pump relay fails).

3) Normal fuel pump operation is the ECM applies 12 volts to the Dark Green/White wire of the fuel pump relay
for two seconds to prime the fuel rails.

If the ECM sees distributor reference pulses (indicating the engine is rotating) it will continue to apply 12 volts to the Dark Green/White wire so the relay continues to be energized and the fuel pump continues to run.

The fuel pump relay has 5 wire going to its relay socket.
Pin A Red
Pin B Black/White
Pin C Dark Green/White
Pin D Red
Pin E Orange

Verify at the relay socket the wires are not shorting out. It's very common for the insulation of the wires
to shrink exposing the copper wire.

If your problem is the fuel pump relay is not closing you need to measure the Dark Green/White wire
while cranking the engine. Should measure 12 volt DC.

No 12 volts the ECM is probably the problem.

If you do have 12 volts the relay should energize and you should have 12 volts on the Red wire on pin A of the relay socket.

If you don't have 12 volts on Pin A Red wire the relay is bad.

 

[jay]

Ecm

So if It is the ECM, the chances are replace? do you have any recommendations?................thanks for your response, it was awesome.........you have the bases covered, thanks
the green/white wire when I turn the key just on position not trying to start it 2-3 volts.........I'll double check while I am turning it over for 12v

There are 3 ways to power the fuel pump.

1)Jump 12 volts to pin G of the diagnostic connector.

2) When engine oil pressure reaches 4 psi the oil pressure switch closes which applies 12 volts from a fusible
link to the fuel pump motor. (This is backup in case the fuel pump relay fails).

3) Normal fuel pump operation is the ECM applies 12 volts to the Dark Green/White wire of the fuel pump relay
for two seconds to prime the fuel rails.

If the ECM sees distributor reference pulses (indicating the engine is rotating) it will continue to apply 12 volts to the Dark Green/White wire so the relay continues to be energized and the fuel pump continues to run.

The fuel pump relay has 5 wire going to its relay socket.
Pin A Red
Pin B Black/White
Pin C Dark Green/White
Pin D Red
Pin E Orange

Verify at the relay socket the wires are not shorting out. It's very common for the insulation of the wires
to shrink exposing the copper wire.

If your problem is the fuel pump relay is not closing you need to measure the Dark Green/White wire
while cranking the engine. Should measure 12 volt DC.

No 12 volts the ECM is probably the problem.

If you do have 12 volts the relay should energize and you should have 12 volts on the Red wire on pin A of the relay socket.

If you don't have 12 volts on Pin A Red wire the relay is bad.

 

[ecss]

Only thing left to verify is if the fuel pump relay coil has a ground.
Use your meter and verify Pin B which is the ground wire at the relay socket has zero ohms
from the Black/White wire to the negative battery terminal.

If that's correct it points to the ECM.

You can also jump a fused (5 amp) 12 volts to the Dark Green/White wire and the relay should close and the fuel
pump should run. This would confirm the ECM is the problem.

If you buy a rebuilt ECM don't forget to remove your Eprom chip from your original computer. The ECM has a small metal cover held on by one bolt. Remove the cover and carefully pull up on the ends of the plastic carrier which the Eprom is held in by. Pull it straight up.

I have a used ECM, if you're interested send me a PM.