five pin relay wiring for elec fuel pump

[waltraud]

Hi,

i have an 83 Dg running LPG and petrol.

Fitting a posiflow electric fuel pump 1.5 - 4psi with relay to speed up changover to petrol and generally make it more relaible as pump worried that stock pump can go dry etc..

Im not quitew sure of all wiring. SO....i think it is terminals

86- ground
30- fused live 12v
87 to fuel pump
87a or 85 ?? from +ve terminal of LPG / Petrol solenoid as a trigger to switch off when running on lpg (no power to solenoid) or on when on petrol (12V to terminal)

so i am left with either 87a (middle terminal) or 85 blank? the idea (thank you Andrew Campershack) is that it defaults to on and therefore feeding the fuel pump if the LPG system fuses and dies....hope this makes sense to someone.

[MidLifeCrisis]

The 5-pin relay looks like this ....



I'm not sure that I understand your description fully but ...

If you wire the following;
Pin 30 - fused live 12v
Pin 86 - ground

Then;
With no 12v signal at pin 85->the 12v signal from pin 30 will be connected to pin 87a
With 12v signal at pin 85->the 12v signal from pin 30 will be connected to pin 87

Hope that helps ....

[ajsimmo]

Ok, here's what you need to know (refer to MLCs diagram above).
The fuel pump feed is wired through Pin 30 and Pin 87a, which are normally connected, unless the relay is energised (12v and earth to 85 & 86) thus throwing the switch and breaking the circuit (switches off power to 87a).
So pin outs are:

85 +12v feed from lpg solenoid (live when on lpg)
86 ground

30 ignition +12v feed (with in-line fuse)
87 not used
87a to fuel pump +12v

Hope that is clear. Any probs give me a call.

[waltraud]

Thank you all, Andrew, that's perfect many thanks,.

[waltraud]

Dear all, some feedback on fitting new fuel pump.

This is going on a 1.9dg with Gasure lpg conversion. I fitted a 1.5-4psi pump with filter in line from the tank. When wired to the five pin relay as described by Andrew above the following happens. On first stage of ignition key turning on the fuel pump runs but then stops when engine started on lpg. The interesting difference to running on a mechanical fuel pump is that when I switch to the middle position of the lpg switch I.e. Petrol flow on and lpg, it does not let petrol in apparently. But when I switch to petrol only on the lpg switch it fires up the pump and picks up after 1-2 seconds. So it works well except for the changeover from gas to petrol it seems. I'm glad to be able to use either fuel again.

[Mocki]

That's why I took the petrol switch off solenoid off altogether and replaced it with the relay for the electric pump - you don't need the petrol switch off solenoid with the electric pump and whilst AJ is right about electrical failure leaving you with no back up I have a switched power source with a spade connector at the relay to be connected if need be , but in 11 years of running on lpg have not once had a electrical problem with the LPG system so it's a low risk . Keep it simple I say

[waltraud]

Thanks Mocki, so with the wiring as it is, if I removed the petrol shut off solenoid the relay kicks in to supply petrol at changeover as required. Thanks bit I don't get is why it worked on mech pump but no electric, at the middle changeover position I mean. Must say that it did feel a bit precarious changing to petrol but effectively with a briefly dead engine.

[Mocki]

Bear in mind my system is the old original type with the three position rocker switch , when I switch from LPG to petrol I go straight from LPG to petrol position not stopping in the middle , but when going from petrol to LPG it is necessary to switch to the middle which supply's no fuel until the carb is empty and then onto LPG
There is only a momentary period of no power when switching from LPG to petrol and a little longer when going from petrol back to LPG as long as it takes for me to switch the switch after the carb Empties

[waltraud]

Ah, well in that case I suspect their is little difference as I realise that to switch over it ideally needs to go quickly via middle position to petrol only.... Ie my switch is push lpg.... Lpg/petrol....... Petrol only...... Off.(drain petrol) .....on-. Back to lpg

[ajsimmo]

Sounds like your switch needs reprogramming to carb emptying only, ie only 3 possible combinations in the cycle:
LPG -> Petrol -> Both fuels off -> LPG... and so on.

How to do this is explained in the booklet that comes with the switch, or if you don't have the instruction booklet refer to the installer. To be honest, many people have the switch set to 3 stage (it's usually set to this by default), and the slight pause waiting for petrol to fill the carb will cease to cause you concern in no time - you just pick your changeover time accordingly.
Look on the bright side though - you can change fuels whilst stationary with no problems at all, just a single quick restart - try that with a mechanical pump and a 3 stage switch! This is precisely why we always advise switching (espesh lpg to petrol) whilst on the move.

[ajsimmo]

On first stage of ignition key turning on the fuel pump runs but then stops when engine started on lpg.

This is why you don't remove the petrol shut-off solenoid. If you do it won't start on gas, because you will have filled the carb with petrol every times you turn the ignition on.

[waltraud]

I see. Thank you, this is very helpful.