Fuel pump not turning on - help please [Archive]

gwmbox

6th October 2017, 10:18 AM

dom14

7th October 2017, 03:12 PM

Hi all, this is related to my other post here (http://www.nissanpatrol.com.au/forums/showthread.php?41013-Fuel-Pump-fail-check-after-LPG-conversion-GU-4-5-Petrol-2000), this post however is related specifically to the fuel pump issue rather than which fuel pump to use.

Auto 2000, GU, 4.5 litre on LPG with Petrol Sub-tank

The car went from working fine to not running on fuel. So I thought it was a the fuel pump.

So ok I have replaced the fuel pump, reconnected the fuel wiring and hoses and installed it all back into the car. I am still not getting any fuel flow and I can't hear the pump going. If I put power direct from a battery to the male blade ends on the top cover of the pump power plug the pump turns on fine. If I reconnect the power plug (two wires) back into the pump, it will not turn on. So I checked fuse and relay, fuse is ok and the relay seems fine. I then checked the power I am getting from the relay plug end and I am getting 12.4v, however when I check the power plug into the pump I am getting 11.6v. I understand there is resistance that can cause this to happen but it appears that the power it is getting may not be enough. I swapped over relays from other relays but still not getting the full 12v at the fuel pump plug wires. There has been nothing changed prior to the pump stopping to work.

My Fuel pump relays are located in the up to 2000 GU model under the glove box, not above the fuses under the driver side dash which is from 2000 models.

I am able to run on LPG fine, but it takes a little extra time to start.

I live rural and my closest 'suitable' mechanic to assist is 130kms away.

Has anyone got any ideas for me to try to resolve this issue

Thanks

Greg

I'm not sure the slightly less voltage is the real reason, but since the pump turns fine if you give it direct power from the battery might have partially diagnosed the problem.

In mine(RB30 dual fuel) had a FPCU(Fuel Pump Control Unit). It's more than a relay as it works as a safety device to cut of the power to the fuel pump in case of an accident( engine stops but the ignition is still on). So, it's piggy backed via oil pressure switch and there is an electronic circuit that triggers the safety action as above. When the ignition is turned on the FPCU allows the power to go to the fuel pump. One of the way this FPCU becomes faulty is not allowing power to the fuel pump when the ignition is turned on. The solution is to either replace the FPCU or wire up a direct priming power line with a push button switch on the dash to prime the pump(Once the engine's started the pump usually gets the power from alternator line which is also connected to the FPCU, but that may also not happen if the FPCU is completely dead). I replaced the FPCU with a LPG tachometric relay(LPG safety switch but used for a different purpose in this case), so the safety cut off job of the FPCU still gets done, but using the ignition signal rather than the oil pressure. For priming, I wired up a direct line to the pump(basically to the pump +12V wire that goes to the above tachometric relay). I also wired up it differently than before, 'cos before the petrol pump runs even when the it is on LPG. Now, the petrol pump runs only when the fuel selector is on petrol. When I wanna switch from LPG to petrol on the road, I just have to prime the pump first using the primer push button switch I wired up for ten seconds or so, and then switch to petrol(so, just enough petrol gets to the petrol cut off solenoid near the carburetor.

Now, how does my above confusing story apply to you?

I suspect either a unit similar to above FPCU or bad connection issue to the ECU that does the above job is affected, depending on yours is a carby or EFI one, and I guess it is EFI.

What I suggest you do is to wire up a direct +12V to the fuel pump and with a separate switch while you try to work out where the real culprit is. Locate the +12v wire that goes to the fuel pump under the dash or under the bonnet and give +12v via a switch on the dashboard. A simple on/off switch will do. I think it should work, even with the not so simple dual fuel setup of EFI engines.

Bear in mind though. Giving direct power to the fuel pump means the above said safety function of cutting of the power to fuel pump won't happen in case of an accident. So, you should only use it as a temporary measure while figuring out where the actual issue is, be it a bad earth, bad +12v line to the pump or something else.