Thread: LPG gremlins...

might be just one of the gas lock offs not working
sounds like it

I'd agree with the others that it's most likely the gas shut-off solenoids which are starving the converter of liquid. To fail suddenly like this suggests a blocked filter is less likely - but not impossible.

There is a solenoid valve on the tank and one on the converter as you've noticed. Both are (usually) energised from a safety relay which is supplied from the ignition circuit via the LPG/petrol changeover switch and this has a control circuit which usually picks up pulses from one of the HT leads to tell the relay that the engine is turning over and needs gas. It usually operates for about 5 to 10 seconds at key switch-on to allow the engine to crank but if it doesn't fire and continue to make spark the control decides the engine is stopped and stops supplying gas for obvious reasons.


The HT lead pulses are often supplied to the safety relay by wrapping a few turns of the control lead around one of the HT leads - check that this hasn't fallen off. The relay usually has an LED on it which lights when it turns the solenoids on - get someone to crank the vehicle while you observe the LED (it's usually under the bonnet). If it doesn't light and sense HT pulses, and the wire is in the right place, I'd replace the relay - it must have some semi-conductors in it to do the job so it's vulnerable.

Don't crank the vehicle more than a couple of times without it starting if the relay LED is on, as it will probably be filling the air intake and plenum chamber with gas and you could get a backfire if you don't let the gas dissipate (you risk blowing the lid off your air-cleaner at best, killing your Mass Airflow Meter at worst). I've had a few backfires early on which have stretched the clamps on my air-cleaner but the MAF survived (it's intake side gauze didn't though).

Good luck - I'll be interested to see the final diagnosis.

Thanks for your input guys.

I started by cracking the line at the solenoid before the converter. Some residual pressure there so a safe bet that the valve and filter at the tank are ok.

Checked the coil here and on the converter for continuity, both good.

Checked the fuses. All good.

Checked the plugs at the switch and safety cutoff. Look ok.

So I hooked up my meter to the cutoff solenoid under the bonnet to check for volts and switched the meter to peak hold.

Switch to gas, turn the key and the bugger starts

I hate fixing stuff and not knowing what was wrong in the first place. You're always left waiting for the other shoe to drop

That's bad luck - now you know your car is one of the walking wounded. Your fault-finding strategy was eminently sensible - my best advice now is to keep a multi-meter in car for when it fails again (which it will, and it will, of course happen at a most inconvenient moment!).

It sounds possible that one of the spade connectors is not properly crimped onto a wire somewhere or one has been crimped onto the insulation and partly penetrated the insulation which has been OK until now. You could go through all the connectors and re-crimp them but there's not much else you can do.

Best of luck - I'll be waiting for the end of the story but it could be a while coming.

I'd actually like a sequential injection system.

Seriously considering taking it to Deacon and getting all but the tanks ripped out and have them start again. Just need to look at the bucks

mongrel *&%$ bustard %^*$ car!

won't run on gas as I head off to Melb (300km away!)

now, if I unplug the ignition safety box and re plug it in, it'll start and run for the preset 2 sec on start up then it cuts the relay to the gas solenoids.

on restart it cuts immediately.

the voltage signal from the ignition coil to the safety box is good.

bypass the box?

Think I found it.

What I thought was the coil signal was the ignition on signal.

no coil signal.

Traced to a quality twist and sticky tape joint

really expected better from the installer if this system

Fixed, I think

I had to recheck a few of my assumptions.

When it ran this morning, it was only because it has a petrol start function that seems to take a while to reboot

When I checked the cut off solenoid before the converter, I checked that it had power and had continuity and I heard it click, BUT I didn't check that it actually switched the gas... It didn't.

Disassembled the valve, filter clear, I can blow through the ports when it's energised, the only thing I can spot is a little magnet in the bottom of the housing covered in crud.

Clean it up, put it back together. It works.

maybe I blew some guff out of the valve?

Anyway, time to hit the highway