S40 keeps switching back over to petrol
 

My 2002 Bifuel factory fit runs on gas for say 15 minutes then switches back on to petrol. I then have to manually switch it back to lpg which it may stay on for another 15 mins before it switches itself back again to petrol. Has anyone any idea what the problem is.
Thanks in advance
Tom

Get your lpg pressure regulator checked, and filter cleaned out would be a good place to start.

You might find that a local LPG indy is better than a Volvo dealer for this.

Cheers

Jack

Local lpg conversion guys wont touch my car because volvo wont release computer stuff to them.

Just taken my S40 bi fuel in to main agent and they did a diagnostic test for £80.
Quoted me £337 to replace gas filter and throttle position sensor, clean throttle housing and adjust pressure. I presume this is the dreaded ETM is it?

They told me that by doing the above work they could not guarantee the fault would be cured. They did say it usually sorts problem out!! Car had been giving trouble switching over to petrol every thirty secs so I was having to continually switch it back to gas.

So what was the £80 diagnostic charge for?

If they can't say what the fault and cure is with certainty then they haven't "diagnosed" the problem.

What happened to mechanics who fixed things? We now seem to get fitters who want to change various parts at our cost on a trial and error basis.

Take off the solenoid valve where the gas goes into the evaporator unit , there will be a 90 degree elbow going into the evaporator/governor, unscrew this and you will find a valve on the end this is the main inlet valve and will stick with deposits after a highish mileage , you can pull the end off and clean the brass pipe it slides on with some scotchbrite or similar , the end piece should be a loose sliding fit , in fact it should fall off if you hold it upside down ...

Gas Attack
 

I'd reckon that if your throttle body etc was duff the car would play up on petrol as well as on gas.

If it runs OK on petrol, but won't stay switched to gas, it's probably a gas-related pressure problem.

If it runs OK on petrol, but rough on gas without switching back, it's probably an ignition-related problem - LPG doesn't tolerate ignition weaknesses, whereas petrol is more forgiving.

Main dealers are probably clueless about bifuels as they don't see them very often. Your dealer sounds worse than most though! Charging £80 to tell you they don't know what's wrong is just pathetic. Don't darken their doorway again.

I'm surprised that the indy LPG fitter are not very helpful. The bit about having no access to Volvo data is highly suspect. If you were oop north I'd have no hesitation in recommending Autogas 2000 in Thirsk. They are the UK main agents for Tartarini, and have connections with good LPG techies all over the country. Why not give them a ring and ask if they can recommend someone local to you? 01845 523 213 is the number you need!

LPG is not scary - it's actually very straightforward, just a matter of finding the right people.

Cheers

Jack

I have to agree with Jack about the throttle body. Sounds like another case of Volvo dealer "stab in the dark" fault finding when it comes to LPG. I've come to the opinion that the computor diagnostics are not very revealing when it comes to LPG. So if it's just a question of using experience and guess work to cure the fault then I'd suggest a good independent has as much chance as a dealer and at a fraction of the cost!

LPG gas pressure switch randomly switching back to petrol
 

Hi,

appreciate this is a very old thread and have read all the comments to what might be the cause of LPG gas pressure switch randomly switching back to petrol.

I have a similar problem where the problem only seems to happen when i've just filled up and the LPG tank is full to capacity.

No sooner have I filled up and driven down the road it will switch back to petrol. I then have to stop the vehicle switch the ignition off wait a few seconds switch the ignition back on and press the button on the switch and it will then go back into LPG mode and then will keep switching back to petrol a bit further down the road.

If I get to some lights I then take the opportunity to turn engine off and back on and this will go on until enough LPG has been used for it to stop switching over.

It seems to run OK once the tank is maybe 90% full !!!!

What is odd is that when the LPG runs empty the switch will switch to petrol as normal and make a bleeping sound and a red flashing LED. To silence the bleep I just acknowledge by pressing the button on the switch and the bleep stops and LED stops flashing but if I press the button again the switch will attempt to go back to LPG and may run again until I give it a bit of throttle and it will switch back to petrol as normal as its running out of gas, but, I can't understand why when it switches over to petrol when the LPG tank is full why it won't switch back to LPG by pressing the button on the switch and why I have to turn the ignition off and back on again for me to get it back into LPG.

The vehicle runs fine when the tank is not full to capacity and I can't fathom what is causing this issue.

Could it be a fault at the rear where the tank is like a pressure valve that doesn't like it when the tank is full?

I have very little faith with most LPG repairers and can only think of one that you mention Autogas2000 in Thirsk.

I have a tartrini ECU and the Vapouriser is situated high up above the matrix and possibly above the coolant level but if this was an air lock problem or vaporiser temperature issue then surely the problem would be all the time but its not and only happens when I fill the damn thing!!!!

You may say well don't fill it to capacity which i'm thinking of doing so but ideally i'd like to use my 60 litre tank.

any thoughts from captain jack and other members most appreciated.

Paul