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[Taxi_Driver]

I was just going to PM Martin about this problem, but thought id make it a post, as im trying understand how the vacuum works and others may be interested too if they dont already know.

Any way the problem is the veccy keeps switching to petrol from lpg when running about town, but doesnt do on high revs.....ie blasting down a motorway.

I took it to vx dealer today who diagnosed it needs a new vapouriser at a cost of £640  
I didnt let them change it and bought the car home.

Ive been having a poke around myself and discovered the following.

Theres a vacuum pipe that comes off the throttle body.....goes to a T junction and one pipe goes to vapouriser.....nothing wrong there......but what i did notice when the engine is running the pipe that comes off the throttle body collapes....took the pipe off and where it was collapsing....it is really soft. I havent had time to replace the pipe yet. But I messed about experimenting and got a bit confused.....so maybe some kind person can explain how it works.
This is what confused me...
Started the car ....waited a few secs and its running on lpg.....i squeezed the vac pipe at where it was collapsed....expecting it to switch to petrol.....but it didnt.....so ok.....i'll pull the pipe off the throttle body....engine coughed a bit but soon recovered and carried on running on lpg.....so next i stuck my finger over the metal pipe going into the throttle body....this caused the engine to stall.

Whats confusing me....is i was expecting the the car to switch to petrol when i pulled the vacuum hose off....but it didnt.
Just my thinking is vacuum pipe to the vapouriser is partially blocked ( coz the pipe is soft and collapsing) .High revs and more vacuum so manages to keep the vapouriser feeding the lpg rail....low revs.. ie town work and not enuf vacuum and vapouriser is switching off

Confused ?? i am at present  :-?

I am hoping changing the vacuum pipe will fix the prob......and its vx dealer overkill that the vapouriser is faulty.  :-/

Cheers

[Elite Pete]

Hi Td Your probably best waiting for Martin to reply but I know you can get repair kits for the vaporizer.

[Martin_1962]

Evaporators are not £640 they are a lot less.

Try a new pipe, from what I can acertain the vacuum pipe controls how much gas comes through - could be too much locking the injector, but more likely low pressure causing a switch over.

Is it after engine braking?

[Taxi_Driver]

Hi Td Your probably best waiting for Martin to reply but I know you can get repair kits for the vaporizer.

Cheers for that Pete, i didnt know that  [smiley=thumbup.gif]

[Taxi_Driver]

Evaporators are not £640 they are a lot less.

Try a new pipe, from what I can acertain the vacuum pipe controls how much gas comes through - could be too much locking the injector, but more likely low pressure causing a switch over.

Is it after engine braking?

That was the fitted price.....vx dealer said its a 4 hour job.....coz where its fitted...they have to take apart some of the sub frame to get to it from underneath.....it does look pretty tight but i reckon you could change it from above.

I will try a new vac pipe tomorrow.....i assume you mean low gas pressure....which is what i thought it would be.....my local lpg installer doesnt know how to check the pressure on this veccy and next nearest vx dealer that does lpg is in glos  

From what ive experimented......no vacuum means loads of lpg......vacuum reduces the lpg feed.....its the only explaination i can see from pulling off the vac pipe and it stills runs on lpg??  :-/

Carnt really say it is after engine braking as you dont do hardly much engine braking running about town.....usually does it in 2nd 3rd maybe slowing or speeding up slightly......they only time it doesnt do it in town is if you floor it through the gears....get stuck in traffic or treat it gently then chances are it switches to petrol

[Martin_1962]

Replace any pipes which look bad, and see if you can get the service kit

[Omegatoy]

Hi TD,
As you have discovered most LPG systems use engine vacuum and lambda signal to set the mixture!!! now then the lambda only fine tunes it a bit so ignore that, but if you have no vacuum then the vapouriser is fully open and chucking in as much gas as possible, as this no vacuum is the same as wot(wide open throttle) which is why the car runs ok on the motorway i think!!
if you are pootling round town on a steady throttle and it gets to much gas , I.E. rich mixture the Ecu will switch it back to petrol because it falls outside the perform,ance parameteres for lpg, its very unusual for a vapouriser to go down, as all it is is a diaphragm(large piece of rubber that moves back and forth to let more or less gas in) really the whole system is so simple thats why people get confused cos they read more into it then needed to!!
So to end a long piece of typing change the vacuum hoses and reset the system 9batery disconnect if youcan remember the radio code etc, and you should find all is ok,
Omegatoy    

[Taxi_Driver]

Hi TD,
As you have discovered most LPG systems use engine vacuum and lambda signal to set the mixture!!! now then the lambda only fine tunes it a bit so ignore that, but if you have no vacuum then the vapouriser is fully open and chucking in as much gas as possible, as this no vacuum is the same as wot(wide open throttle) which is why the car runs ok on the motorway i think!!
if you are pootling round town on a steady throttle and it gets to much gas , I.E. rich mixture the Ecu will switch it back to petrol because it falls outside the perform,ance parameteres for lpg, its very unusual for a vapouriser to go down, as all it is is a diaphragm(large piece of rubber that moves back and forth to let more or less gas in) really the whole system is so simple thats why people get confused cos they read more into it then needed to!!
So to end a long piece of typing change the vacuum hoses and reset the system 9batery disconnect if youcan remember the radio code etc, and you should find all is ok,
Omegatoy    

Thankyou Omegatoy.....your explanation sounds good to me  [smiley=thumbsup.gif].....i'll give it a go tomorrow and report back  [smiley=thumbup.gif]

One question tho....will disconnecting the battery reset anything?...just thinking of my Omega facelift....disconnecting the battery on that wont reset any codes.....is it the same on a vectraC (can based) or is it for another reason?  :-/

Cheers

[Omegatoy]

cant answer for sure mate but i always thought a disconect for ten mins would restore factory setttings!!! however i could be wrong!!!!
Omegatoy

[Martin_1962]

I don't think powering off LPG ECU will do much - but you could just drop the fuse

[Taxi_Driver]

Ok....i got hold of 1m of vacuum pipe this morning....and after it stopped raining i set about changing the vac pipes.

I changed the vac pipe from the throttle body to the T piece, this was the pipe that was collapsing.
Then for good measures and coz i had to buy 1 metre of the stuff, i changed the vac pipe from the T piece to the vapouriser and then changed the pipe from the T piece to, well i dunno what it is to be honest, but whatever it is, its a small rectangular block that has a 3 wire connector going to it.....must be summat to do with the lpg.....coz i played about and disconnected the plug from it and when i started the veccy it wouldnt switch to lpg....reconnected it and it then would.

However its made no difference to it I did think id fixed to start with....coz i drove 8 miles thro traffic and doing town work and it stayed on lpg all the time....then it switched back to petrol and from then on every fews mins it keep switching back to petrol  

I did look at taking the vapouriser out......as i did find on the net....that the diaphram inside it can perish....plus i think it has another filter inside it that can block up...not sure tho  :-/

But it looks a right pain to get out....i reckon theres enuf clearance to take it out from above....but one of the gas pipes and water pipes is on the underneath side....so think that will be a prob without getting it on a ramp and accessing those from underneath.

I did call Millbrook today...for advice an maybe booking it in with them...they said they'll call me back tomorrow.....its just as Millbrook did the conversion for vx to start with....id rather trust them if they tell me it needs a new vapouriser than a vx dealer!!

Any thoughts guys??

[Auto Addict]

Buy a diesel next time?

[Martin_1962]

Well I don't know what it is but evaporator service now sounds quite likely

[Taxi_Driver]

Buy a diesel next time?

Wrong answer AA  

[Taxi_Driver]

Well I don't know what it is but evaporator service now sounds quite likely

May do Martin.....tho im still sure its something pretty simple....3yo car with 78k on it...hopefully  :-/

Unless Omegatoy can come up with something....i think Millbrook may be the way to go  :-/