LPG/Petrol switching issue

[dom14]

Hey guys,
This sounds like an electrical problem.

Mine is a GQ RB30 manual carby on dual fuel.

If I start on LPG and then switch to petrol(when the engine is still relatively cold), it works fine.
But, once the engine is warmed up and I try to switch to petrol from LPG(directly, as there's no need to leave it in the middle position when switching from gas to petrol),
it doesn't work.
I get out of the car while the switch is still in petrol position and opened up the bonnet. There's no petrol goes into the carby.
I switched the ignition off and switched on again. Here it works, the carby's getting fuel.

I have these theories as where the fault is, and going through them one by one.

1)Faulty dashboard LPG/petrol switch
2)Faulty petrol solenoid under the bonnet
3)Faulty pump(petrol pump is actually inside the tank, 'cos the it's been upgraded to a long range one by the previous owner).
4)There's a slight petrol leak(if the tank is filled above a certain line, say...half tank or so) from the fill line where it connects to the tank.
This may be causing some vacuum issues with the pump??!!
( I simply need to replace the hose, but didn't bother so far, 'cos I never fill the petrol tank enough to leak from the fill line that way and hardly drive on
petrol)

Have I missed anything? Do I need to check anything else. Fuel filter and the little carby filter is fine. So, I don't think there's any petrol blockage in filters.

[Agronaught]

My car won't switch from lpg to petrol at idle. Push the button and the led with flash until the engine is above 1k rpm and then it will switch.

Not sure if that helps at all.

[dom14]

My car won't switch from lpg to petrol at idle. Push the button and the led with flash until the engine is above 1k rpm and then it will switch.

Not sure if that helps at all.

It won't switch from LPG to petrol at idle on this carby model. I think that because it needs bit more engine power to get it going for few more revs until some petrol gets into the carby.
So, I always had to rev it high when I switch from LPG to petrol. But, this is a kind of exercise I usually don't do. Because, I usually start on petrol and then switch to LPG. There's very little need to do the other way around, but previously there was no problem doing it though. Now, I do have a problem doing that.
Even though I rarely need to switch from LPG to petrol, not being able to do that once the engine is warm, indicates a problem that needs immediate attention.
I'm hoping it's not the fuel pump, because the fuel pump is inside the tank.

[Bigcol]

have a look at ALL of the earths for the relays - both Gas and Petrol
make sure they are clean and tight

is yours electronic ignition?
do you have an immobilizer?

when you switch off the petrol, it drains the fuel bowl -
hence why you have the "neutral" position on the switch (Gas - off - Petrol) to run out the petrol, as it will over fuel (choke) it you went straight from petrol to gas

when going from Gas to Petrol - there is NO petrol in the Carby - hence having the rev's up or it stalls

with my old GQ, if going from Gas to Petrol, I would do it if I was at 80kms, by the time I got to 70, the fuel had filled the bowl, and was now running on petrol........

it didnt matter if it was hot / cold / rain / wind etc....

check ALL of the earths, and the connectors - if they look dodgy - fix them there and then

and remember - only go from Gas to Petrol if your moving..........

[Bigcol]

Hey guys,

4)There's a slight petrol leak(if the tank is filled above a certain line, say...half tank or so) from the fill line where it connects to the tank.
This may be causing some vacuum issues with the pump??!!
( I simply need to replace the hose, but didn't bother so far, 'cos I never fill the petrol tank enough to leak from the fill line that way and hardly drive on
petrol)



get this fixed ASAP..........
this is a time bomb waiting to go off............

and I dont think its just the fuel hose either................................

[dom14]

have a look at ALL of the earths for the relays - both Gas and Petrol
make sure they are clean and tight

is yours electronic ignition?
do you have an immobilizer?

when you switch off the petrol, it drains the fuel bowl -
hence why you have the "neutral" position on the switch (Gas - off - Petrol) to run out the petrol, as it will over fuel (choke) it you went straight from petrol to gas

when going from Gas to Petrol - there is NO petrol in the Carby - hence having the rev's up or it stalls

with my old GQ, if going from Gas to Petrol, I would do it if I was at 80kms, by the time I got to 70, the fuel had filled the bowl, and was now running on petrol........

it didnt matter if it was hot / cold / rain / wind etc....

check ALL of the earths, and the connectors - if they look dodgy - fix them there and then

and remember - only go from Gas to Petrol if your moving..........

Hi mate,
It's carby model.
Yes, it does have an immobilizer, but I'm in the process of replacing it(haven't started yet).

Yes, I understand I can't switch from petrol to gas straightaway. The problem is the other war around, but not all the time.
And it doesn't appear all the time. I couldn't get it to reproduce it last couple of days. But, on Monday(rainy day), I started the car on gas.
Then drove to hundred meters or so, and stopped the engine, because something on the side of the road attracted my attention.
Then I tried to crank after a minute or so, I couldn't get it to start. I switched to petrol, same thing.
Then I put in the middle and cranked for few more seconds and it reluctantly started.

I sense, there's a mixture or electrical and fuel system issues in this car, which I need to sort out one by one.

About switching from LPG to petrol straightaway, I've never had problems with it before regardless of the speed.

What's happening here is that fuel is not getting into the carby when switching from LPG to petrol at times. And so far from what I've experienced it's when the engine is hot.
The heat of the engine may have nothing to do with it. But, there's definitely an electrical issue with the fuel pump or the petrol solenoid near the carby(or some loose connection somewhere else). I haven't been able to locate the problem, 'cos I haven't been able to fault it at will. The problem produces itself whenever it wants.

These electrical problems are hard to diagnose and real PITA at times. I'll do my best and if not I may have to get it to a auto electrician.

Thanks for the post

[dom14]

get this fixed ASAP..........
this is a time bomb waiting to go off............

and I dont think its just the fuel hose either................................

I agree with you 100%. It is a time bomb, no doubt.

The reason I've been slack with the issue was that I once temporarily 'masked' the problem with the combination of rubber tube wrap+glue.
That was holding it for a while. The fuel fill hose is not the stock one. Just the plastic/fibreglass one from Long Range Automotive in Lilydale, installed some twenty years ago or so.
It has shrunk over time and need replacing. But, it's a quite a PITA job to replace it(I attempted before realizing it's a bit harder than I thought it was, then simply patched it for the time being)
I won't even contemplate on going for a long trip without sorting out this issue/these issues(there's more than one I reckon).

At the moment I'm bit lost with how to locate the problem location with these LPG to petrol switching issue, which only produces itself at it's own whim.


P.S. I did take it to the regular local auto electrician. He couldn't get it to fault, so he returned the car with no charge and asked me to keep an eye on it.

[Bigcol]

mine was also a carby model with a Sprint Gas mixer on top of the Carby - 1989 GQ

then it is definitely an earth problem
with a dodgy wire connection

I had an earth fault with the immobilizer - which would stop the fuel but not the Gas - even when already running
I had an earth fault with the electronic ignition - which made it hard to start in Petrol and run in petrol (when hot) but would start and run in gas
I had another earth fault with the electronic ignition - which wouldn't let it start or run in either fuel - for about 5 days, then one day it started ok........ go figure
I had a fault with the Tachometric Relay - which gave problems on switching on BOTH gas and Petrol

all of the above were happening at the same time.......

I had 2 different Auto Electricians look at it and could not find anything wrong with it
I replaced the Coil 3 times
and I threatened to burn it,........

I spent 11 months, and many many hours trying different things until I fixed ALL the Connectors and the Earths
and replaced some of the wiring that was looking old and frail

I also ran another earth from the Main Battery and one from the Aux battery to the chassis and also to the body

good luck..................

[threedogs]

GQs and GUs are nortorious for earthing problems,
@ Big Col I can see why you wanted to burn it.
I would suggest to all who read this to run extra earths from the battery to the chassis and the body.
Toyota earth different sections of the vehicle like motor area ,front cabin area , cabin and cargo area.
so being a Nissan too many earths cant be that bad a thing

[dom14]

mine was also a carby model with a Sprint Gas mixer on top of the Carby - 1989 GQ

then it is definitely an earth problem
with a dodgy wire connection

I had an earth fault with the immobilizer - which would stop the fuel but not the Gas - even when already running
I had an earth fault with the electronic ignition - which made it hard to start in Petrol and run in petrol (when hot) but would start and run in gas
I had another earth fault with the electronic ignition - which wouldn't let it start or run in either fuel - for about 5 days, then one day it started ok........ go figure
I had a fault with the Tachometric Relay - which gave problems on switching on BOTH gas and Petrol

all of the above were happening at the same time.......

I had 2 different Auto Electricians look at it and could not find anything wrong with it
I replaced the Coil 3 times
and I threatened to burn it,........

I spent 11 months, and many many hours trying different things until I fixed ALL the Connectors and the Earths
and replaced some of the wiring that was looking old and frail

I also ran another earth from the Main Battery and one from the Aux battery to the chassis and also to the body

good luck..................

Thanks Col.
That's an amazing amount of pretty damn useful information with enlightenment, 'cos now i see the problem in a different light.
I have no doubt it's gonna help me with locating the problem.
I'm having pretty much all those four problems except that I'm yet to figure out what and where's the Tachometric Relay.
Also, I need to do quick homework on the immobilizer wiring.
But, I know for a fact, my GQ's got some pretty amateur backyard wiring on it.
I've replaced a fair bit of it few months back. I'm again at it.

I don't think mine has electronic ignition, looking at the dizzy. It looks like either after market or the stock point ignition system.
I'll post a picture shortly to get some advice on that.

It's a real PITA to locate these wiring problems, but I have no other way but spending time on it.

No wonder you wanted to burn the GQ, but I'm glad you didn't.:D

GQs can drive you crazy with the electrical problems, no argument there.

[dom14]

GQs and GUs are nortorious for earthing problems,
@ Big Col I can see why you wanted to burn it.
I would suggest to all who read this to run extra earths from the battery to the chassis and the body.
Toyota earth different sections of the vehicle like motor area ,front cabin area , cabin and cargo area.
so being a Nissan too many earths cant be that bad a thing

Yep, I'm onto it. Before, I blame the 'faulty' fuel pump & fuel solenoid, I need to check every friggin wire possible.
I know that's how the pro auto elecs fix jobs when they can't locate the problem location. They simply rewire.
That's probably I would have to do as well.

[Bigcol]

Thanks Col.
That's an amazing amount of pretty damn useful information with enlightenment, 'cos now i see the problem in a different light.
I have no doubt it's gonna help me with locating the problem.
I'm having pretty much all those four problems except that I'm yet to figure out what and where's the Tachometric Relay.
Also, I need to do quick homework on the immobilizer wiring.
But, I know for a fact, my GQ's got some pretty amateur backyard wiring on it.
I've replaced a fair bit of it few months back. I'm again at it.

I don't think mine has electronic ignition, looking at the dizzy. It looks like either after market or the stock point ignition system.
I'll post a picture shortly to get some advice on that.

It's a real PITA to locate these wiring problems, but I have no other way but spending time on it.

No wonder you wanted to burn the GQ, but I'm glad you didn't.:D

GQs can drive you crazy with the electrical problems, no argument there.

I know that feeling, when I wanted to upgrade the headlight wiring harness, I had problems
took a week to re-wire (and get rid of the crap in there) the headlights & hi-beam & spotlights for their own relays
stood back when I had finished - and you couldn't see I had been under there for 6 days.........
which was a good thing
but a bad thing
cause I then had a hard time explaining it to myself what I had done, let alone anyone else......

[Bigcol]

Yep, I'm onto it. Before, I blame the 'faulty' fuel pump & fuel solenoid, I need to check every friggin wire possible.
I know that's how the pro auto elecs fix jobs when they can't locate the problem location. They simply rewire.
That's probably I would have to do as well.

take your time, and start near the Battery.......... and do 1 wire at a time................

I had some, when you went to put the clip off the relay, the wire fell off in your hand

just take your time....

"slowly slowly, catchy monkey"

[dom14]

I know that feeling, when I wanted to upgrade the headlight wiring harness, I had problems
took a week to re-wire (and get rid of the crap in there) the headlights & hi-beam & spotlights for their own relays
stood back when I had finished - and you couldn't see I had been under there for 6 days.........
which was a good thing
but a bad thing
cause I then had a hard time explaining it to myself what I had done, let alone anyone else......

I haven't touched the headlights on mine yet. I installed driving lights, but had them wired by and auto elec, so it shouldn't give me any grief, hopefully.

BTW, the only way to remember what you've done, especially when it comes to electrical stuff is to document them. I draw diagrams or take photographs or both.

When I had problems with indicators blinking fast and battery not charging, I was able to work out the problem with the help of the forum. It was pretty bad backyard wiring done
by a noob. I was shocked to see the cheap and dangerous way it was done(fuses sticky taped to wires, 20 amp wire for a 60 amp line, etc). The wires were badly corroded & cooked inside.
Only discovered when I cut open them.

[dom14]

take your time, and start near the Battery.......... and do 1 wire at a time................

I had some, when you went to put the clip off the relay, the wire fell off in your hand

just take your time....

"slowly slowly, catchy monkey"

Yep, mate. I will get there eventually.
Cheers