HELP...... loss of power on lpg at higher revs

[GADGETP38]

1991 v8 3.9

It's always been fine and would pull hard to 5k but just recently after about 3.5k she losses power and wont pull, almost as if running out of gas, but it's full.
Runs fine at all revs on petrol.

Anyone got any ideas?

Cheers in anticipation.

[Rich_P]

What's LPG system have you got fitted?  Multi-point?  Single-point?  Electronic single/multi-point?

[Skibum346]

What's the mileage... and does it only do it on LPG?

[nickW]

my 3.5 disco does this a bit on both LPG and petrol is there a reason for it

[GADGETP38]

single point electronic and yes only does it on gas.   done about 112k

 :(

[Rich_P]

Electronic.  Hmm, doesn't that use some sort of sensor in the exhaust to determine the mixture and adjust accordingly?

[GADGETP38]

dunno;Wouldnt have thought this one has. The exhaust is rudimentary to say the least...... straight through with a cherry bomb.
I know it is single point and I only say electronic as there are loads of wires going to all sorts of places, but I thought they were for the engine management system to make the injectors think they were still fueling etc.   I am pretty sure its a pretty basic system.

[Rich_P]

Ooh, okay.  I understand what system you now have.  You have the basic single-point injection.

The electronic type I was asking about will automatically adjust the mixture to get the best out of the system.

Here's what I think may be the problem with your LPG kit.  The pressure provided by the system may be lacking a bit, causing the engine to run lean at higher rpms.  Or it may be the vaporiser that needs servicing/replacement (they only last a few years).

I would try increasing the gas supply pressure on the LPG system to see if that helps further up the rev range or not.

[Skibum346]

my 3.5 disco does this a bit on both LPG and petrol is there a reason for it

Well, assuming that it's the origonal engine... it could be a worn camshaft. We have a 94 RRC with just over 200k on the clock and it's now gutless. I understand that the wear of the cam usually points at changing it at the 100K mark. I think we're overdue!

As yours is a 3.5, I suspect that you will also have high mileage and hence camshaft wear. Hate to be the bearer of bad news!

[nickW]

mine on about 130k i dont normally bother to rev it over 3k as the power seems to go very flat

[Range Rover Blues]

Blue does this sometimes, I just put it down to the LPG kit being past it.  Funny but it will pull in one gear then change up and it won't pull, or vica-versa.  I'll try cleaning it if it ever stops raining.

Remeber LPG will loose power at the top end as it takes physically longer to burn, even with the timing cranked forwards it will still happen, you actually need a different advance curve for LPG.

[barnhill4x4]

Have you looked at the LPG Filter? What Air Filter do you have?

[sardonicus]

If it has a steppermotor thingy before the inlet point try turning this up (out) quarter to half a turn,or the other way (RRB?)
THe vapouriser may have a drain plug in the bottom ,undo this and drain any oily deposits out.

[Range Rover Blues]

If it's the stepper motor then it will be controlled by the electricery, ie the lambda sensor.  If it's manually adjustable then yes you can try it turned outward to increase gas flow but you will find a very narrow margin in which it will run.

Try cleaning out the evaporater, I also find the thin Ali plate in mine gets bent and messes up the mixture.  TBH it's ready for the bin, I'm not a big fan of draw-through systems anymore but they keep getting sold as they are cheap, better to get a single point system as a bare minimum.

[GADGETP38]

thanx everyone, hopefully if the weather is ok this afternoon I'll get chance to try a few ideas.  Will keep you posted.   :D

[Garth]

Could be the diaphram in the vaporiser?