disco2 v8 misfire

[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]

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

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

[Range Rover Blues]

P.S. you daid the garage had had the engine apart? did they skim the heads? if so do you know what gaskets were fitted to them?

[remmy7]

Hi all,

Here goes first of all Extremeteam I am in Kirkcaldy. The heads were skimmed but I have no idea what thickness of gasket has been used. I have just been out and disconnected the MAS and whilst it was slightly worse on gas it was just the same on petrol. The engine seams to pull very well regardless of incline once above 4000rpm, idles with a slight burble and revs freely, it is only when it is put under load at lower rpm that it doesnt want to know and begins to mis and backfire. Re the timming issue I know that the timming sensors on the crank were replaced at the rebuild but you have to excuse my ignorance here but again I assumed that the engine management made the appropriate calculations therefor I have know idea about the initial set up of timming I just assumed that the bloke knew what he was about.(just realised that there are a lot of assumptions here and I know what that makes). Lamda sensors were replaced around 20000 miles ago.

Thanks again Remmy7

[Xtremeteam]

remmy7

do u fancy a wee trip over?
im in the garage today stripping a dif but if u wanted to u could pop round & ill have a wee look & can discuss

[thermidorthelobster]

Crank sensor is also a possibility worth considering.

Do you have an electronic unit which adjusts the timing on LPG?  If so, some have a bypass setting.  You want to get it running sweetly on petrol before you worry about the LPG, and bypassing as much of the LPG paraphernalia as possible is a good place to start.

[Xtremeteam]

Hi all,

Here goes first of all Extremeteam I am in Kirkcaldy. The heads were skimmed but I have no idea what thickness of gasket has been used. I have just been out and disconnected the MAS and whilst it was slightly worse on gas it was just the same on petrol. The engine seams to pull very well regardless of incline once above 4000rpm, idles with a slight burble and revs freely, it is only when it is put under load at lower rpm that it doesnt want to know and begins to mis and backfire. Re the timming issue I know that the timming sensors on the crank were replaced at the rebuild but you have to excuse my ignorance here but again I assumed that the engine management made the appropriate calculations therefor I have know idea about the initial set up of timming I just assumed that the bloke knew what he was about.(just realised that there are a lot of assumptions here and I know what that makes). Lamda sensors were replaced around 20000 miles ago.

Thanks again Remmy7

give me a call on 070 if u want to come round

[daveyravey]

Sounds like one of the dodgy rotor arms again    as this sounds quite like what mine was doing

[Xtremeteam]

Sounds like one of the dodgy rotor arms again    as this sounds quite like what mine was doing

doesent have rotor arms,is pure coul packs being a thor engine running Gems managment

[remmy7]

Hi all,

Just to let you know on Sunday night I took a look in complete darkness under the bonnet and the left hand bank of leads were lit up like a christmas tree. Hoping to change them today and further hoping that this is going to cure the problem. If not Mike has pointed me in the direction of a local chap with good diagnostics. My only concern now is that the difference between the misfire on gas and petrol is so pronounced that I may have an additional problem with the gas but again I am hoping that this is due to the different ignition requirements. (its now next to impossible to drive on gas)
I will let you know how I get on once the leads have been changed as its a B***er of a job to get at the coils.

Cheers Remmy7.

[remmy7]

Now it gets even more interesting (thats not my true thoughts)
True to form the wrong leads were delivered and I now await the correct ones. However the engine has been put on the diagnostics and was showing mis fires on 5 and 8 (familiar numbers) at Idle nothing was apparent so we drove the car with the diagnostics connected and this revealed a faullty knock sensor apparently ( I am not personally conversant with the test book thingy) As well as the leads a knock sensor is now also enroute. The only thoughts I have is wether or not the Knock sensor is merely a symptom or can a faulty knock sensor be the cause of the misfire in the first place. As I am really into territory completely unknown to me (bring back distributors and SU carbs that can be serviced using an old penny) any advice/info would be appreciated.

Cheers Remmy7

[Range Rover Blues]

All I can say is suck it and see.  The sensor is faulty, so need swapping, as do the leads.  Then you need to have it diagnosed again :roll:

[Skippy]

Be aware that the "thor" generations of rover v8's required a apecific type of spark plug to be used as any other will play havoc with the miss fire detection system!

The genuine is an Champion RC11 PYPB4 double-platinium spark plugs, you will know when you have the correct type, as they are about £8 each  :shock: .  Be sure that they have fitted the correct type!!

[remmy7]

Hello everyone,

I said I would let you no how I got on, well unfortunately I had to take a two week break from the stress of being a disco2 owner(2 weeks of driving a 5.7 v8 chevvy bliss) on returning to the uk airport the disco had gone flat at the rear end and it took 80 miles before it came back up, but at least it did although I couldnt raise it to the off road position. Took the car to the garage the following day to get the leads and knock sensor changed and it appears that the engine is running well. I say appears because the damm thing is still there, the suspension refused to come back up when it was taken of the four post lift. After 3 hours of p***ing about with the diagnostics which revealed unknown fault code 0000 (helpfull) we put a direct feed onto the compressor and nothing happened. We even tried using the airline to fill the accumulator tank but the exhaust valve is in the open position. To further complicate matters the ACE warning light has come on and is staying on. It would appear that a new compresor is needed and also a switch on the ACE valve block (apparently a common fault as the garage say they have changed three recently) we are only guessing at the switch fault as the diagnostics are not picking anything up. Hopefully tommorow will see if hte garage are correct in their diagnosis and hopefully I will have the vehicle running as it should for the first time since december (my wife never fails to be impressed with my eternal optomism). The only observation I would make at this point is how the hell can so many seperate things go wrong with a vehicle that is getting little use due to so many diverse faults its only been working and on the road for about three weeks in the last six months. I think its time to get another 300tdi I never had a single fault on that one in ithe six years I had it until that is I was rudley awoken by the fire service trying but failing to save it from being burnt out (some sort of electrical short in front of the bulkhead near to the steering column.

Regards Remmy7.

[Range Rover Blues]

Well oddly enough now that I don't drive Bllue every day it's sulking, loads of stuff is going wromg imncluding the PAS I've fixed twice already.

[remmy7]

Hi Folks,
Dont really want to tempt fate but here goes anyway. Current state of play is suspension is now working correctly. ACE didnt require anything as is rectified itself when the suspension was fixed. Engine ran on petrol but not at all on gas, it wasnt firing on two of the offside bank of cylinders. Subsequent check revealed that the garage had put the manifolds back on and caught the two supply pipes between manifold and head. The manifold was taken off by a more local LPG installer and the pipework was smartened up (the original installation and subsequent engine work had it looking like spaghetti). Guess what --------------------------------------Its running. Seems a tad down on power from what I remember and is keen to change down at the slightest incline on motorways but others have tried it and now reckon this is due mainly to running it on 265/70's instead of 255/65's. Its now a waiting game as its been running for or at least out of a garage for 4 hours. I hope to source some rock/tree sliders before it goes sick again but if the wife sees the repair bills she will throw a wobbly.

Cheers Remmy7.