LPG on V8,problems?

Hello
i have my range rover 3.9i v8 with LPG converted and ,here in Portugal, some mechanics tell me that it "kill" the engine. My range rover have 155 000 KLM (about 75 000 miles).
One strange noise that i ear is "TAC TAC TAC" when the engine runs in idle (only when it is hot. when the engine is cold, there are no noises).
Do you know what´s the problem?

LPG shouldn't cause any issues with a healthy engine.

The noise you have is possibly a cam follower, might be worth trying some fully synthetic diesel oil such as Shell Helix in the engine for a few thousand miles to see if it clears, if not then you'll need to change the lifter and possibly the cam.

Peter

thank you for the answer.
I think that isn´t the cam followers.
if the problem are the cam followers,they should make the "tac tac tac" with the engine cold right?
The "tac tac tac" only appears when the engine is hot..

How loud is the noise? Can you hear it from inside the car for example?

When your engine is at hot idle, this is when you have lowest oil pressure. As soon as you give it throttle, the oil pressure goes up and fully pumps up the lifter. So it may well be the cause. The oil pressure will normally be higher on cold start, and then settle down when warm - so don't rule out Peters answer.

worn rocker arm 100% as for the gas not damaging the engine changed plenty for gumed valves and no comp due to piston rings glued to the pistons due to the oil being burnt away by the gas also running to hot and cooing the engine to this i have tuned my engine and get 22 mpg so no need for gas!

Jon14 said:

How loud is the noise? Can you hear it from inside the car for example?

When your engine is at hot idle, this is when you have lowest oil pressure. As soon as you give it throttle, the oil pressure goes up and fully pumps up the lifter. So it may well be the cause. The oil pressure will normally be higher on cold start, and then settle down when warm - so don't rule out Peters answer.

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Thank you for the post. The noise is very low..Inside the car i can´t hear anything, only outside. I hear the noise since i bought the car, and i done 5000miles +/-, and the noise kept the same (neither lower, neither higher).
So, i have to change the rock arms RV8 Rocker Shaft+steel arm kit - V8 Tuner and the cam followers STD Rover V8 cam followers (Quality Brand) - V8 Tuner .These are ok, right?

I´ll start changing the cam followers first.
Another thing that some mechanics says, it´s about the worn of the main bearings.
Rover Main Bearings 3.5,3.9,4.2 - V8 Tuner

Can it be?

'tac - tac' at piston speed when the engine is warm/hot, as opposed to valve gear noise(half engine speed) when the unit is cold could well be caused by a slipped liner. Some scources say that this problem can be aggrevated by the high combustion chamber temperatures that result from prolonged LPG use. Try switching over to petrol whilst driving with an engine at running temp. & see if the noise stops after a couple of miles, only to return when you re-select LPG. Hopefully I'm wrong (been there myself!)

with ONLY petrol, the noise is the same...when the engine is hot, the TAC TAC TAC comes in idle

another thing:

my 3.9i engine is very very slow...for example in the highway, in 5th gear, i can´t go at 60 MPh when is in one small rise...i have to reduce for 4th, and some times to 3th
i have 285 85 R16 tyres.

is it normal??
my engine maybe is "dead"

bakuuu said:

with ONLY petrol, the noise is the same...when the engine is hot, the TAC TAC TAC comes in idle

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If it's a liner then the 'tac - tac' will increase in direct proportion to the engine speed. If I'm right & switching over to petrol does'nt alter the noise, then it's probably because the problem has been there for a while. This test worked on my 3.9 at first but, like your's, had no effect after a few hundred miles. There is no reason for a slipped liner to effect performance as such & 75k is no distance at all for a 'maintained' V8. Although valve gear wear is not unheard at that mileage I would'nt have thought it serious enough to effect performance. If it does turn out to be a slipped liner then you are looking at a replacement block, which could well sort out your performance issues as well although I think your choice of tyre size is overgearing the car when used on the highway.