LPG installation query - 940 LPT

[BreadBin]

I have a problem getting my 940 to run on LPG, someone had made a right mess under the bonnet which I have just about cleared up now however I don't think my LPG system is properly connected. Currently the vacuum pipe to the vapouriser is T'd into the idle control valve which I'm not sure is correct. To my understanding this should only ever see negative pressure (vacuum) but in this configuration boost pressure would blow the diaphragm the wrong way - or have I got that wrong?
I'm thinking that the pipe should go before the turbo so it only ever gets sucked on! I want to get it serviced but would rather reduce any work they have to do that I can do myself before hand..

[classicswede]

To give correct advice I need to know what make and type of system you have eg OMVL, Zavoli prins etc and if it is a mixer system or multi point injection.

On the asumption that it is multi point injection made by one of teh AEB based systems such as KING OMVL or Romano etc then the vacuum pipe should be connected directly to the manifold. Both the map sensor on reducer should be connected together via a t peice to their own decicated vacuum port on the manifold. If they are T'd into an existing line then chances are you will be getting false readings. There are pleanty of spare ports on teh manifold that you can use without drilling in a new one if you dont want to drill the manifold.

The AEB based systems need to have the vapouriser compensated for manifold pressure as that is how the fuel map is set out. This is to keep the rail gas pressure constant over manifold pressure.

If you were to connect the vacuum line to the air intake pipe pre turbo the system would run very very badly. It needs the manifold pressure to keep the gas pressure high enough on boost as well as for correct mapping.

If it is a mixer system then the vacuum pipe is much bigger at about 16mm bore and is connected to teh back of teh regulator. It is known as a balance pipe and is used to put pressure on the vapouriser diaphram when under boost to make it boost sensitive. These systems are very tricky to set up and most often tend to actualy need a slight bleed off to keep teh balance pressure at a minium under high boost.

Hopfully that will give you reasonable explination of how it all works.

BTW Prins and Landi systems do not normaly connect the vacuum pipe to teh reducer.

[BreadBin]

Hi there, sorry I shoud have given more info
Its a single point OMVL system on a standard LPT 940, at the moment it will idle on gas but any throttle pressure causes it to die immediately. Someone had roughly cut a hole in the turbo to intercooler pipe and jammed the balance pipe in there with no sealant (complete with a plastic T-piece on the end..), there was also a hole cut in the hard pipe from intercooler to throttle body which was wide open and may have been used for the balance pipe too with some serious bodging elsewhere so it didn't run very well at all but would actually drive on LPG! I've fixed all the leaks and thought the balance pipe looked like it had been on the idle valve take off (with the aforementioned T-piece) so tried it there.
I've tried to set it up using the just off stalling method but it just won't play, so clearly a service and professional setup is the order of the day - I'd just like it to at least be in a usable configuration when I take it there!
Thanks for your advice

[classicswede]

The balance pipe need to be fitted in the pipe between the intercooler and the throttle housing. In the balance pipe there should be a restrictor valve as per the fuel miture valve. The balance pipe valve normaly wants to be fully closed alowing the minimum flow to the back of the vapouriser. In some cases you need to drill a small bleed off hole into the elbow on the back of the reducer to bleed away some of teh boost pressure on teh back of teh reg. About 2mm usualy does the trick.

The problem with the OMVL balanced reducer is it is not a turbo one but for balancing a mechanical air flow meter. The best way to make the OMVL one to work on a turbo is to fit a vacuum pipe to teh primary stage of teh vapouriser to keep teh gas pressure a set pressure over manifold as per injection ones. To do this you will either need a cover from a injection reg or drill and tap your existing one for a vacuum nipple. If you alter your existing one you will also need to block of the hole inside that alows exessive pressure to bleed off into the low presure chamber.

If you are going to an installer to have this done talk the conversion over with them and make sure they have experiance of mixers and turbo's. Most installer will have never touched a conversion like this. In the early days I did a few but would never mixer one again. Multi point is realy the only way to go on one of these to be fair.

[BreadBin]

Thankyou for the advice, I'm rapidly going off this car and may well get rid of it.