Hi David have you looked at fuel pressure in the rail just thinking it will only be misfiring on petrol if only doing it on cold or does it misfire on lpg just after first switching over?

It sounds more like fuel starvation. What about the adaptations have they been reset ? Mind you I never do mine as it seems such a lottery as to whether it will settle again

I'll start it up tomorrow David and have a listen for you. Would try now but I'm halfway through a bottle of glenfiddich so won't be much help now

It’s worse when the car is on petrol as that’s when it’s at it’s coldest, however, it’s still not right when it switches to LPG.

After 15 - 20 minutes of driving, by then it’s properly warmed up, it’s as smooth as silk.

David. 2002 4.6 Vogue SE - Alveston Red with Lightstone Leather
2007 Range Rover Supercharged in Java Black with Ivory Leather
2012 Range Rover 5.0 SC Autobiography in Indus Silver with Jet/Ivory Interior
2012 Range Rover 4.4 TDV8 Autobiography in Baltic Blue with Sand Interior

Just a thought David is the engine coolant sensor working properly if it is showing hot when cold it will underfuel just a thought

That’s a good thought, Sandy. I’ll go and read it with the IID in a minute and see if I get a sensible reading.

Actually, I might leave it till the morning as by then it should be the same as the ambient temperature.

I did wonder if it’s possible that the crank sensor might not be behaving when it’s cold. 2002 4.6 Vogue SE - Alveston Red with Lightstone Leather
2007 Range Rover Supercharged in Java Black with Ivory Leather
2012 Range Rover 5.0 SC Autobiography in Indus Silver with Jet/Ivory Interior
2012 Range Rover 4.4 TDV8 Autobiography in Baltic Blue with Sand Interior

It has to be something like that something is telling it to lean to normal operating temp could even be the maf the main thing in my opinion its nothing too serious and cant be carbonisation as it has changed too quickly so more like a sensor breaking down
I can check readings on mine as and when and if you need it although mine is on 220k now

I did wonder about the MAF, however, when looking at the IID tool this evening, one of the live values is “Target MAF” and when comparing that to the actual reading it’s near as dammit so I’m kinda ruling out the MAF in my own head.

If you listen to the drivers side of your engine, can you hear a hissing or whooshing type noise Sandy? Around the vacuum pump area.

This one has done it since I got it despite having the PCV and pipe seals replaced. The local specialist said it’s just air flow in the PCV system you can hear but I don’t remember my old one doing it… however, it’s 5 years since I last saw that car!

David. 2002 4.6 Vogue SE - Alveston Red with Lightstone Leather
2007 Range Rover Supercharged in Java Black with Ivory Leather
2012 Range Rover 5.0 SC Autobiography in Indus Silver with Jet/Ivory Interior
2012 Range Rover 4.4 TDV8 Autobiography in Baltic Blue with Sand Interior

I've had another quick look this morning...

I selected a few options to view under Live Values with the IID Tool.

From the Engine ECU:

Engine Coolant Temperature
Fuel Rail Temperature
External Temperature

From the Instrument Panel ECU:

Engine Coolant Temperature

Here's the results:

Click image to enlarge

Click image to enlarge

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Click image to enlarge

Looking in the workshop manual the fuel pressure should be 335kPa (3.5bar) at idle with the A/C switched off. When I looked at it and saw it sitting at 303kPa the A/C was switched on so I'll do that test again.

The manual states that's where it should be sitting when using a pressure gauge so am wondering if the IID isn't measuring it in quite the right place either.

Although I don't think low fuel pressure on petrol would account for it not running right on LPG though. As far as I'm aware it's the injector timing that the LPG monitors, not the fuel pressure.

David. 2002 4.6 Vogue SE - Alveston Red with Lightstone Leather
2007 Range Rover Supercharged in Java Black with Ivory Leather
2012 Range Rover 5.0 SC Autobiography in Indus Silver with Jet/Ivory Interior
2012 Range Rover 4.4 TDV8 Autobiography in Baltic Blue with Sand Interior

Hi David as far as the whooshing noise goes no nothing like that on mine also I had to replace the pressure sensor on mine a few years back but it just stopped. I dont know enough about how the ecu's speak to each other but if the fuel rail is running low on pressure will that not be picked up by the leg ecu and adjust accordingly ?

Mine reads at ignition on 358 idle 380 1000 rpm 303 then 303 at 2000

That was warm so will do it tomorrow when it is cold or when I come out of work

David, does it have a fuel return line fitted with the appropriate orifice?
Or does it have an emulator...

This one has a fuel return line fitted with a pressure bleed valve in the rear quarter. It only gets power when the car is switched to LPG.

I've just been out and checked the fuel pressures again this evening:

Ignition on (2nd time today) - 350kPa.
Idle - 303kPa (when warm)
1000rpm - 303kPa
2000rpm - 303kPa

When giving it a blip of the throttle I could see the fuel pressure spiking at 400 and something kPa.

I drove to my folks tonight to get the car into the workshop and noticed that when under load be it accelerating gently through the village I get no misfires displayed on any cylinders.

When climbing the hills out of the village there are 0 misfires on any cylinders.

When slowing at a junction and the rpm drops back to under 1000 there are misfires that start to be logged.

When idling on my folks driveway the misfire counter was still climbing slightly on all cylinders but nothing like what it does when it's cold.

Switching the car from petrol to LPG at this increased the rate at which the misfires were being logged but not massively.

I've convinced myself that this has to be an air leak somewhere so am going to focus on that I think as there's nothing else that I can think of that would cause these symptoms.

David. 2002 4.6 Vogue SE - Alveston Red with Lightstone Leather
2007 Range Rover Supercharged in Java Black with Ivory Leather
2012 Range Rover 5.0 SC Autobiography in Indus Silver with Jet/Ivory Interior
2012 Range Rover 4.4 TDV8 Autobiography in Baltic Blue with Sand Interior