RRC 3.9 EFI Fuel Pump issue

[roule35]

Hi,
After rebuilding the engine, the fuel pump doesn't work . I checked:
- the main and fuel pump relay ok
- inertia switch ok
- fuel pump 3 pins connector : 5 volts on the blue wire (gauge) OK , O volt on the green one...
- fuel pump relay socket (blue one) : I have 12 volts on the pin 30 and 86 but nothing on the 87 pin even when i bridge 85 and 86 ??
- no voltage on the C40 fuse circuit on the main board (fuse is good)
- no voltage on the coil (+ battery and - coil pin) - condenser seems ok.

Don't know what to check after ... and what to replace battery (old one) , coil ...
Thanks for advices.

[stevieturbo]

roule35 said:

Hi,
After rebuilding the engine, the fuel pump doesn't work . I checked:
- the main and fuel pump relay ok
- inertia switch ok
- fuel pump 3 pins connector : 5 volts on the blue wire (gauge) OK , O volt on the green one...
- fuel pump relay socket (blue one) : I have 12 volts on the pin 30 and 86 but nothing on the 87 pin even when i bridge 85 and 86 ??
- no voltage on the C40 fuse circuit on the main board (fuse is good)
- no voltage on the coil (+ battery and - coil pin) - condenser seems ok.

Don't know what to check after ... and what to replace battery (old one) , coil ...
Thanks for advices.

And if you power the pump manually does it run ? Elaborate more as to why you believe the pump itself is at fault ? And what work was done during this rebuild ?

The pump motor/load should be on pin 87, with 12v fused supply at pin 30. Bridging 30 and 87 should energise the motor.

Bridging 85 and 86 at the relay socket could short something and cause damage. I can see no reason you'd ever want to bridge those as those are the relay coil/trigger wires. 86 typically being a 12v and 85 being a ground.

[GreenV8S]

Seems like you have an electrical problem on the switched ignition circuit, perhaps aggravated by you shorting out the fuel pump relay.

I'd start by diagnosing the problem on the ignition switched supply. You should have battery +ve voltage on the coil +ve supply while the ignition is on. If not, check for blown fuses, pinched wires, missing earth straps, alarm/immob upset and so on.

Once the ignition switched supply is fixed you may still need to fix whatever you may have damaged on the fuel pump circuit.

[roule35]

stevieturbo said:

And if you power the pump manually does it run ? Elaborate more as to why you believe the pump itself is at fault ? And what work was done during this rebuild ?

The pump motor/load should be on pin 87, with 12v fused supply at pin 30. Bridging 30 and 87 should energise the motor.

Bridging 85 and 86 at the relay socket could short something and cause damage. I can see no reason you'd ever want to bridge those as those are the relay coil/trigger wires. 86 typically being a 12v and 85 being a ground.

Thanks, i 'll try to bridge 30 and 87
The pump prime with a external 12 volts (i hear it) but not enough to eject fuel from the pipes...may be another issue...

[roule35]

GreenV8S said:

Seems like you have an electrical problem on the switched ignition circuit, perhaps aggravated by you shorting out the fuel pump relay.

I'd start by diagnosing the problem on the ignition switched supply. You should have battery +ve voltage on the coil +ve supply while the ignition is on. If not, check for blown fuses, pinched wires, missing earth straps, alarm/immob upset and so on.

Once the ignition switched supply is fixed you may still need to fix whatever you may have damaged on the fuel pump circuit.

Thanks
No voltage on the coil (multimeter on the + battery and - coil = O volt), may be try with a direct wire battery to coil ...

[GreenV8S]

roule35 said:

No voltage on the coil (multimeter on the + battery and - coil = O volt),

You need to be measuring voltages from battery -ve, not coil -ve. The coil is negative-switched so is only connected to the battery via the ignition amp. I'm not sure what you were planning to connect to the battery, but if you were thinking of connecting the coil to the battery then there are some ways that could go badly wrong.

This shows how a little knowledge can be a dangerous thing. No disrespect intended, but are you sure you want to try to diagnose this yourself? You appear to be in danger of making things worse.

[stevieturbo]

roule35 said:

Thanks
No voltage on the coil (multimeter on the + battery and - coil = O volt), may be try with a direct wire battery to coil ...

As Green says....find someone competent to diagnose this, as it sounds like you're going to cause more harm than good with your current level of understanding.

[roule35]

GreenV8S said:

You need to be measuring voltages from battery -ve, not coil -ve. The coil is negative-switched so is only connected to the battery via the ignition amp. I'm not sure what you were planning to connect to the battery, but if you were thinking of connecting the coil to the battery then there are some ways that could go badly wrong.

This shows how a little knowledge can be a dangerous thing. No disrespect intended, but are you sure you want to try to diagnose this yourself? You appear to be in danger of making things worse.

You're right, I have 12 volts between - battery and + coil. i recovered the 1991 manual to check precisely the connections...

[roule35]

Finally, i found the inertia switch is bad (was good before my rebuilt ???), i bridge it and now i have 12 volts on the fuel pump connector... BUT the fuel relay cut just one second after ignition instead 3 or 4 seconds...what could be the issue ?

Edited by roule35 on Saturday 30th August 15:32

[GreenV8S]

The pump is normally only powered for a short priming pule when you switch the ignition on, and when the engine is actually turning.

[roule35]

GreenV8S said:

The pump is normally only powered for a short priming pule when you switch the ignition on, and when the engine is actually turning.

short, ok but one second ...shouldn't be enough , right ?

[GreenV8S]

roule35 said:

short, ok but one second ...shouldn't be enough , right ?

It's normally about two seconds.

If you get power applied for about 1 - 2 seconds when you switch the ignition on, I'd assume that's working as intended and move on.

[roule35]

The pump prime but no benzine comes out...i took it of the tank, test it in a water bassine, prime bur nothing out...
Two years ago before my rebuild the pump was fine ...may be time to change it...i 'm not sure the sender unit could be repair...

[GreenV8S]

If you have power to the pump, and the pump is not pumping, then that suggests the pump is faulty.