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disco2 v8 misfire

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remmy7:
Hello there I am new to this forum and only discovered it whilst attempting to gain information re a problem i have so perhaps someone may be able to help. Here's the story so far My current disco is a 2000 lpg converted v8 that developed a misfire on both lpg and petrol it lacked power and as a result would change down constantly at the drop of a hat at motorway speeds (although its currently running on BFG AT's at 265/70 x16 so the gearing may be slightly affected). As a result it has now had 4 airflow meters and each time this has helped for around a thousand miles. The engine was was rebuilt with the heads skimmed and faulty valves replaced new piston rings etc etc around two thousand miles ago as it was losing compression on cylinders 5&8. Again when it was put back together it wasnt right and this resulted in the 4th airflow meter. It the ran well for approximately the 2 thousand miles when it began to misfire on LPG (this immediately after a little offroad use) after a few hundred miles on petrol alone the misfire is now appearing on both (although its far worse on LPG) This is how the problem has manifested itself each time and it gets progresively worse until the engine starts to backfire. Has anyone got any suggestions (clean and constructive ones please) as at present the engine has already had in the region of £3000 spent on it and doesnt appear to be any better. There have been occasions however when the engine has run and pulled well it would just be great if it could be relied upon.

Cheers Remmy7.

Range Rover Blues:
Right I can understand your frustration and I'd love to be able to helpo, we all would I'm sure.

Firstly and most obvious.  LPG is hardfer to ignite than petrol so the plug gaps need closing up from 30thou to 27 thou, don't ask me in metric :roll:

What were those 2 cylinder loosing compression, valves or rings?

Who is advising you to swap the AFM, I'm not convinced that after 3 of them that is the cause TBH.

Have you had it connected to a diagnostic computer (not just a tuning machine but a propoer code-reader like Rovacom).  My Rovacom would be able to tell you what inputs the engine is seeing.

Try driving it with the AFM disconnected.

What engine management does the car have, if is Lucas Hot wire 14CU or is it the later Gems/Thor or whetever.

Where are you?

remmy7:
Hi range Rover Blues,
Thanks for the reply, for your info I am in Fife Scotland. The engine is the Thor type and it was the garage that I bought it from that has changed the Airflow meters it was also them that stated that the compression was down on 5&8 when stripped they said that the valves were well and truly coked up (strange for gas I thought) I have no idea what diagnostics the bloke was using I have seen him use it but the garage is an alleged 4x4 specialist not a franchised Land rover dealer. Would disconnecting the air flow meter remove the fault if it is the cause or would this throw the engine management into utter confusion. I now have a craving to return to diesel although I prefer the power of the v8 when its working
Re the plug gaps again the garage state they and the leads are all fine but I am inclined to change them anyway.

Thanks for your help Remmy7

Xtremeteam:

--- Quote from: "remmy7" ---Hi range Rover Blues,
Thanks for the reply, for your info I am in Fife Scotland. The engine is the Thor type and it was the garage that I bought it from that has changed the Airflow meters it was also them that stated that the compression was down on 5&8 when stripped they said that the valves were well and truly coked up (strange for gas I thought) I have no idea what diagnostics the bloke was using I have seen him use it but the garage is an alleged 4x4 specialist not a franchised Land rover dealer. Would disconnecting the air flow meter remove the fault if it is the cause or would this throw the engine management into utter confusion. I now have a craving to return to diesel although I prefer the power of the v8 when its working
Re the plug gaps again the garage state they and the leads are all fine but I am inclined to change them anyway.

Thanks for your help Remmy7
--- End quote ---

in which case your in my neck of the woods.
Where if fife are you? im at lochgelly.

Range Rover Blues:
The later engine management is much better than the 14CU/hot wire system and I know for a fact that mine runs with the MAF (hot wire) sensor missing, it has Lamda sensors too so there is some redundancy in the system, ie you can loose one or more senosrs and the ECU can 'guess' from the other sensors and stay in control.  SO if it is the MAF sensor then try driving without it.

That said it could possibly be a faulty Lambda sensor, conflicting with the MAF sensor.

Don't be surprised about the valves, LPG is very dry, once you egt sorted I suggest a valve-saver kit that drop oil into the inlet stream to protect the valves.

Blue has done at least 3 valves whilst we have had it :shock: but that's partly downto incorrect timing

Check this, is the timing correct for PETROL? some people over-advance LPG engines to make use of the incredibly high octane rating of Propane, roughly 115 :o

Are you anywhere near Mike? if so I'd suggest a trip over :wink:

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