Won't start on gas but fine once running.

[PSI250]

Have a D1 3.9 v8, dual fuel.

Has developed a problem where it will not start on gas. Cranks and cranks but no fire. If I'm lucky on very first crank I get a tiny kick but nothing after.
If I give a a squirt of brake clean down the intake it will start instantly and run fine on gas.
Same deal if I start on petrol and as soon as it starts I can flick to gas it runs perfectly fine. I can go the rest of the day starting ok on gas but come the next morning will not start. Starts and runs fine on petrol and once running is fine on gas.

Can hear solenoids clicking etc and gauge lights up etc. Pretty sure I Can smell gas while cranking. No intake leaks
Up untill recently used to start on gas really well.
Replaced plugs as had been in awhile but made no differance.

Any ideas? Have not played with gas that much before.

[Tombie]

Bee Utey is the man to get in touch with...

I'd hazard a guess and say vacuum leak or diaphragm in gas converter is failing - But wait until you hear from BU.

[bee utey]

LPG is difficult to start on a cold engine unless the mixtures are exactly right at the time of firing the spark plug. Most LPG systems fitted to EFI vehicles use a timing relay that allows the petrol injectors to run for about 1-2 seconds after you start cranking. The engine actually fires on petrol and the gas hits the cylinders just as the timer cuts off the injectors. Problems like yours with cold starting are usually something like

1. the timer adjustment is out so the engine doesn't get enough petrol in the timing period.

2. The timing relay is wired wrong so that it cuts out if you don't hit the starter instantly.

3. The petrol is stale or the injectors are slightly out of whack so the engine doesn't fire quickly from cold like it should do.

4. The LPG idle mixture is too rich and is flooding the engine.

Basically if it starts normally on petrol there's nothing wrong with just using petrol for the initial start and gas for every other start. The reason that it starts easily when warm is because the engine spins faster, the gas is already present in the air intake at the correct mixture from the last shut down, and the battery is charged so the spark is adequate to fire it instantly.

What can I suggest you do based on the above? Very little until I have detailed knowledge of what kind of system you have, how the timer is wired, what spark plugs you have, what their gap has been set to, what your ignition timing is set at, what sort of ignition module you're running, how good your battery is, how tightly your plug lead boots fit on the plugs and cap, etc. etc.

Shorter answer you probably need a good LPG fitter/tuner to cast their eyes over it.:)

[PSI250]

Thank you for the replies.

I was possibly thinking too rich but timer issue does sound more plausible as has only really started in the last few weeks. Nothing changed, was ok one day and worse the next.
Plugs are new bp6es's leads are tight and good condition
Wiring has not been changed / touched recently.
Timing should be about 5-10deg btdc and has not been changed recently.
Standard ignition module
Battery is in good condition.
No notice in increased consumption once running on lpg.
Unsure of system or timer location, will investigate further on weekend.

Will try a noid light on injectors also and see if there pulsing on lpg start up.

Thanks again.

[scarry]

Our old neglected Mitsy spare van always has issues starting on LPG in cold weather.

We always start on fuel then manually switch to LPG.

Once the weather warms up,no problems at all.

The van also has a very small battery,so once it has starting issues,it doesn't take long before it is flat:mad:

[PSI250]

just to update this as i finally got time to investigate further.

so wouldn;t start on gas if left for any period of time ( at work, overnight etc), but would always start on petrol so all i had been doing was manually switching to petrol for every start, then as soon as it started i flicked to gas and happy days.

Recently i noticed it was taking ever so slightly longer to start on fuel and the pump was getting slightly louder in operation. decided at $140 i'll happily throw a pump in it, plus who knows how many times in its history its been run out of fuel by previous owners. ( small 1/4 fuel tank)

replaced pump, now quiet operation, starts quicker on fuel AND STARTS ON GAS!
(well by gas i mean when the switch is left on gas as even on gas it will use petrol for initial start)

so i'm tipping since i started have starting issues with starting when switched to gas it was the pump unable to maintain pressure up to the rail when left for a few hours, on gas it would give its quick fuel pump prime on ign but not long enough to get enough pressure to start. On petrol this wasn;t so noticable as it would give a longer prime and continue to pump on cranking.

new fuel pump in and hasn;t had any trouble starting on gas, and i reckon i get better power on petrol now too.


i do have an intermittant immobiliser issue ( on both fuels ) which i will start another thread on but least this issue is sorted.