Thread: Start on Petrol or LPG?

Originally Posted by Cannon

Hi all,

I have SVI on my 2003 V8 which starts on petrol then switches to LPG when it warms up.

Just wondering what the benefits of starting like this are as opposed to starting on LPG?

It's mainly about meeting emissions, a warm converter functions more reliably than a cold one, meeting euro emissions specs better. It also stops the risk of flooding the engine with excess gas from a cold converter if the engine is shut down too soon. Basically it's idiot proofing. I've had to raise the temp for changeover for a couple of vehicles as changeover coincided with the end of their driveway or a major downhill intersection and stalling/rough running resulted.

Some systems have an emergency over-ride procedure to allow cold starting on gas, in case the petrol system is faulty. If your system has a push button for change over try holding down the button before the gauge lights come on, crank it with the button still down, see if it starts on gas. It may run a bit rough as the fine settings for cold running aren't there.

Thanks mate

It does start on gas by holding the button in.

I like idiot proof just wondering

i had long reach ute on gas, and my mechanic all ways told me to start it on petrol. cant remember why tho.
super useful post i know.

I dont think my BRC-Impco injected system has an emergency LPG start...

Cheers

The last couple of ford utes I owned, where very difficult to start on gas, It was much easier to start on petrol and then use gas for the rest of the trip.
The benefits are also that its keeps the petrol fresher if you use some occasionally, this stops corrosion in the tank with water collecting.
The engines also have little wear on gas and thus running on petrol when cold beds the rings and keeps the bores in better shape.
I had a lot of trouble when using ethanol petrol in duel fuel applications due to the fuel going stale very quickly, it cost me a fuel pump real quick, since then I only put the real petrol in duel fuel cars.
It is also good to keep at least a quarter of a tank of petrol in a lot of late model cars, if the fuel pump is located in the tank it is cooled by the fuel, if the tank is empty your fuel pump may overheat ....

Mixer type dual fuel systems on EFI vehicles generally start with a short burst of petrol. If they don't start well on LPG the petrol timer is likely out of adjustment or incorrectly set up. Running a dual fuel engine on petrol when cold is only shortening its life. Rings don't need bedding in each morning. My wife's old P76 did 400,000km on straight LPG and still has perfect compression figures. It also started easily when cold every day because of the right choice of high energy ignition and plug gap adjustment.

My old 85 carby Rangie starts on LPG from cold even if it has been sitting for a week,I have to remember not to touch the pedal as I do in my series or it is a petrol start run for a few K's switch all fuel off & run the carbies dry and switch to LPG as the engine dies,as I was instructed to do all those years ago.

Originally Posted by UncleHo

My old 85 carby Rangie starts on LPG from cold even if it has been sitting for a week,I have to remember not to touch the pedal as I do in my series or it is a petrol start run for a few K's switch all fuel off & run the carbies dry and switch to LPG as the engine dies,as I was instructed to do all those years ago.

Both my old 81 and 85 rangies were the same, i usually did the fuel changeover on the highway if possible or coasting, except i used to floor it from cold to start it on lpg with the old impco system fitted.