Should the fuel pump run while on gas?

robbo_yobbo · 28-05-2006, 07:08 PM

I'm 80% through turning my Factory EGAS system into an aftermarket setup independant of the ecu but now have myself stumped.

I have an GASTEC LPG processor which starts the car on fuel before switching to gas. When it switches to gas it shuts down the injectors but has no contact with the fuel pump (as far as i know).

My question being.......... Will the ECU shut off the fuel pump on its own when it realises the injectors dont need more fuel, or will it keep pumping away building up pressure??? or will it stay on but not be a problem?

When I originaly set up the wiring, I had a relay switching off the fuel pump manualy whenever the gas was turned on, But after a bit of thought, I realised the car wouldnt be able to start if it was switched to gas, as the processor needs the fuel pump for the 1st few seconds.

Anyone who can shed some light on this dilema is a top bloke!

XR6-VCT-2000 · 28-05-2006, 07:32 PM

Hmm I'm not sure to whats going to happen with the fuel pump , weather it will shut off or still be powered but just not pump cos the injectors don't require fuel. The previous setup you had shutting off the pump sounded good and a safeguard, a possibility to making it work with this system would be to use a single switch with a 6-pin post setting on the rear of the switch ( so 2 modules/objects can be switched on or off with the 1 switch ) , wire the relay for ya fuelpump up to the switch aswell so it switches on and off with the gas/fuel selected by the switch . you could use a 3 way switch with a 8-post rear too , so for the 3 ways u have eg .. 1. GAS setup.....2. Switch off GAS and start/stop the fuel pump ... 3.. FUEL setup . thats if you need the fuel pump running for a second or so before the fuel system is engaged.

robbo_yobbo · 28-05-2006, 07:45 PM

Quote:

Originally Posted by XR6-VCT-2000

Hmm I'm not sure to whats going to happen with the fuel pump , weather it will shut off or still be powered but just not pump cos the injectors don't require fuel. The previous setup you had shutting off the pump sounded good and a safeguard, a possibility to making it work with this system would be to use a single switch with a 6-pin post setting on the rear of the switch ( so 2 modules/objects can be switched on or off with the 1 switch ) , wire the relay for ya fuelpump up to the switch aswell so it switches on and off with the gas/fuel selected by the switch . you could use a 3 way switch with a 6-post rear too , so for the 3 ways u have eg .. 1. GAS setup.....2. Switch off GAS and start/stop the fuel pump ... 3.. FUEL setup . thats if you need the fuel pump running for a second or so before the fuel system is engaged.

The thought had run through my mind, only problem being that I spent the extra on the petrol startup processor so I could avoid having to switch it by hand every time the car is started.
The only other thing I can think of would be to have a 5second timer before the relay so that the fuel pump runs for another 5 seconds after it's switched, which would allow the petrol startup (while on gas) as the relay turns the petrol back on while cranking because theres no accsessory power to the relay.

If Im lucky, someone will tell me the fuel pump would stop pumping on its own??? fingers x'd hay.

XR6-VCT-2000 · 28-05-2006, 08:00 PM

Oh i got ya ;) - but can't tell ya if the fuel pump will stop running , i wouldn't have a clue ..lol , I'm sure someone here will know though ;) ....maybe.... But if you can't get an answer in the end - i can't see why, obviouslly you use a switch to switch from gas to fuel and vise versa , it should be just a matter of getting 1 switch which operates like 2 seperate switches (so the switch doesn't cross the circuits of the 2 different switches inside the 1 switch ) , then wire the relay to the switch also , so it powers on and off no matter what according to the way you setup the wiring on the switch according to your gas/fuel selection.

mash · 28-05-2006, 08:05 PM

The pump should continue to run without any problem as it is a return system and helps keep the injectors cool.

XR6-VCT-2000 · 28-05-2006, 08:07 PM

Oh actually - sorry - after re-reading your post a bit more i properly see your problem now . Like if the car has been left on gas when it was turned off , then goto restart the car while still with the switch set to gas , but the GASTEC LPG processor needs petrol for the first few seconds as it starts on fuel first before switching over automatically... hmmmmmmmmm ...

robbo_yobbo · 28-05-2006, 08:26 PM

Quote:

Originally Posted by XR6-VCT-2000

Oh actually - sorry - after re-reading your post a bit more i properly see your problem now . Like if the car has been left on gas when it was turned off , then goto restart the car while still with the switch set to gas , but the GASTEC LPG processor needs petrol for the first few seconds as it starts on fuel first before switching over automatically... hmmmmmmmmm ...

BINGO! lol, I know there's a solution, just a matter of finding it!

JC · 28-05-2006, 08:26 PM

Yes, fuel pump runs - only the injectors are switched off when running on gas.

XR6-VCT-2000 · 28-05-2006, 08:30 PM

Well there ya go , thanks JC as i was interested to know too after it was asked , setups sure have changed over the times since the old carby setups with gas ;) .

robbo_yobbo · 28-05-2006, 08:31 PM

Quote:

Originally Posted by mash

The pump should continue to run without any problem as it is a return system and helps keep the injectors cool.

Now That's the sort of answer I was hoping for!
Being that I know a little about everything but alot about nothing, would it be possible to elaborate on what you mean by a return system??
I'm pretty sure my processor just sends a resistance to the ecu to make it think that the injectors are still pumping away, does this mean that the exess fuel pumped by the fuel pump but not used by the injectors is just returned to the fuel tank, thus causing no exess presure thus no problem??
I hope thats what you meant, as it solves my whole problem!!

robbo_yobbo · 28-05-2006, 08:33 PM

Quote:

Originally Posted by JC

Yes, fuel pump runs - only the injectors are switched off when running on gas.

Woah, your too fast for me, already answered my last question before I asked it!
Cheers guys, Now I can focus on a few other car problems instead!

mash · 28-05-2006, 08:42 PM

fuel pump runs at a higher pres than the in jectors require and goes through a regulator controlled by vacumm (on the end of the fuel rail) and the returns to the tank. The bigger the throttle imput the less vacumm and higher the fuel pres. to increase fuel to the injectors when required. You can buy a time delay relay so that the car starts on fuel and gas and the fuel shuts off after a given time (range is usually 0-2 sec) this allows time for the gas to flow from the converter to the cylinders. You can sometimes feel the change as the fuel shuts off. relay can be used if computer system is not used.

Marhleet · 28-05-2006, 08:56 PM

if the pump don't run, it will go senile and forget how to .....
more importantly, the fuel in the injector area (rail) will get hot, evaporate away, and you'll have sludge in the injectors in the morning.
which is why, on the non auto start on petrol system, we start on petrol now and then to blow the injectors out.

if you've seen an old XD.. taxi on straight LPG, the petrol tank has black crap coming out of it. ugh

TURBOTAXI · 28-05-2006, 09:13 PM

The pump will continue while the car is on LPG.

I dont think all the horror stories about not using injectors is warranted. I have reconnected a fuel system that had been disconnected for years (pump running dry and fuel lines disconnected, and once reconnected it ran like a clock. Good economy good power.

If you use a rising rate reg and boost with a duel fuel setup, you must have a manual switch installed to turn the pump on and off, otherwise you create massive pressure in the fuel system and end up rupturing the fuel lines.

robbo_yobbo · 28-05-2006, 09:27 PM

Quote:

Originally Posted by TURBOTAXI

The pump will continue while the car is on LPG.

I dont think all the horror stories about not using injectors is warranted. I have reconnected a fuel system that had been disconnected for years (pump running dry and fuel lines disconnected, and once reconnected it ran like a clock. Good economy good power.

If you use a rising rate reg and boost with a duel fuel setup, you must have a manual switch installed to turn the pump on and off, otherwise you create massive pressure in the fuel system and end up rupturing the fuel lines.

Now that I didnt want to hear, but is what I was concerned about! I dont have any boost, and I dont have any reason to believe it's anything other than a standard regulator, Is the standard a rising rate or adjustable? how would I know/check to be on the safe side?

JC · 28-05-2006, 10:43 PM

You would only using a rising rate regulator in a blown application, or highly developed NA. No need to worry on a stock standard dual fuel setup - your fuel pump, lines and injectors should all remain OK.

robbo_yobbo · 28-05-2006, 10:52 PM

Quote:

Originally Posted by JC

You would only using a rising rate regulator in a blown application, or highly developed NA. No need to worry on a stock standard dual fuel setup - your fuel pump, lines and injectors should all remain OK.

Awesom, thanks again