Air Bypass Valve ? LPG Idle Problem ?

[fireblade]

Hi, thank you for letting me join the club.  I can't find any info on this so I am after some help.  1991, 3.9efi Range Rover with LPG.  LPG was disconnected before I bought it.  I have reconnected it all works but idle is now at 2500rpm but only on gas.  On petrol it is slightly eratic but normally 500 or 600 rpm.  No miss fire on either fuel.  

I have tried swapping the air by pass valve but no change but I don't know if the other was any good either. When I take the by pass valve out it is in the fully closed position, is this normal?  Could a faulty bypass valve make it rev so high or do you think it is just throwing in so much gas it forces the revs up ?  Thank you for your help and also with other issues I have read about in the forum.
Thank you  Graham :roll:

[skip]

Sounds to me like you've got a vacum leak and running lean on gas.

[Range Rover Blues]

Usual wisdom is get it running well on petrol, then sort out the gas.

What sort of gas system is it?  is it single point, draw through or multipoint?

Have you got the Haynes manual? if not get one, it's actully ok for the RRC and it might be worth you chcking something called the base idle speed, the idle speed with the bypass valve fully closed should be about 500RPM or thereabouts.

The valve will be fully closed when you take it out, unless you unplug it with the engine running then remove it.

If you leave the ignition on with the engine stalled you might hear the bypass valve wind out then in again once every couple of minutes.

[Rossko]

It's possible that the LPG system is wired to turn off the petrol injectors in a clumsy way that kills the petrol ECU.  The ECU needs to stay alive when running on LPG because it also controls the stepper idle valve ...

The LPG control ought to only cut power to petrol injectors.  Quite often it has been wired to cut the power to the airflow meter too, which could prompt the petrol ECU to think it's in big trouble and set the idle speed to failsafe i.e. high.  It's also possible the LPG control has been wired to kill the power to the ECU altogether, freezing the idle motor at the point of changeover.

There'll be a reason it was disconnected ;)

good luck, Ross K

[fireblade]

Hi, the rangie is fixed and now runs better on LPG than Petrol.  The fault was with the stepper motor.  I had tried another old one but that was obviously no good.  Thanks for the comments though,
Regards  Graham

[Range Rover Blues]

SO how much was a new one then :shock: