Thread: Rough running v8

Plug leads are a very common problem and will often only be noticed under load. Mine began to fail at 160k. Bugger of a job to replace but just possible without removing too much. I had 2 fail at the same time so perhaps yours has too? I had my doubts at first but sure enough 2 had gone, one from each coil.

MAF - mine failed at more or less the same time just to confuse matters. Mine showed no codes but did result in delayed gear changes, hesitation etc. The gear change issue sounded strange but it's not unknown with MAFs failing as the ecu links both engine and transmission (see Ashcroft transmissions FAQ). Basically pre failure it would change into 4th at about 60 kph, after failure at about 80 kph and all up changes appeared generally delayed. A new MAF and all returned to normal. I would add that most people would not even notice the change but when you've had a car since new you get used to it.

My O2 sensors are original, never had an issue and fuel consumption remains the same as it was when new so I'm sure they're still ok.

Added re other common problems on a Disco of that age so you're prepared...:-

My front propshaft failed at about 120K. I simply got some new U/Js and rebuilt it - took about about 2 hrs tops. I doubt that your problem relates to this shaft. Mine only manifested itself with a slight vibration at around 100kph. Since i did the exact same journey everyday any change became obvious. It was just about impossible to detect any play with the shaft on the car.

3 Amigos. yep, same thing here about twice/year. I got a reset tool from the US and it flags a faulty OSF sensor after every incident. Not worried about it as it always resets and the abs/tc works fine.

Chirping noise - can't comment!!!

Ignition lock - spray some lithium grease into it to help lube before it fails (Jaycar) - another 150K fix for mine.

Window winder mechanisms - welded mine the first time when the spot welds failed and then manufactured a metal slider plate when the nylon wheel failed. Doubt it will ever fail again!!!

Airbags - my Disco was a special order base 2001 SE but with ACE and SLS. The airbags begin to droop after about 10 years. 15 mins/side to replace.

Parts sources - all UK. Much cheaper and genrally more info.

I am on to my second mechanic now after the first one declared it was running fine. 10 metres up the road it was shuddering.

Second mechanic changed all the plugs and said it ran fine. I didn't even get I out of the drive way before taking it back. Just because the computer says there is nothing wrong with it doesn't mean it is not shuddering itself to bits. Even though I told them it is vibrating badly between 1750 and 2000 rpm under light load once before I have told them again and will see how I go. Flogging the crap out of it in neutral isn't always the best way to gauge general running conditions.

I have asked them to look at the front drive shaft too just in case. Very frustrating!

Can't get it booked in to proper land rover mechanics for 2 weeks but it isn't a Ferrari so surely an A grade mechanic can fix it?

Around Brisbane I wont use anyone other than MR Automotive at Redcliffe, never had an issue with them and they know Land Rovers inside and out.

In relation to your shudder and chirping sound, I have had to replace the following items on my 2002 V8.

1. MAF and O2 sensors, this did not cause a shudder, just a huge loss of power and crazy fuel consumption with black smoke under acceleration.
2. Front drive shaft uni joints, I have had the original one rebuilt and I rebuilt a second spare that I keep at home.
3. I had a chirping sound that ended up being the bearing in the air con compressor, I had this rebuilt by an auto air place when I was in Rocky for work.
4. Rough running engine, this was due to the original leads. I had new ones made by a place at Kallangur, I dont think he is there anymore but they where about half the price of other leads and larger / better insulated etc.

I really doubt the plugs were an issue. btw - if he really did replace them, what with, it matters on the D2?

The same applies to the front prop shaft. If it's really so bad that you notice it at such low speed then it's been shot for ages and who knows what the downsides might be.

Why did the 2nd mechanic choose to fit new plugs and not touch the leads? Too easy to do the former? New leads are a bastard of a job.

You won't always get error codes from leads or indeed a bad MAF sensor. Also, being a V8, they tend to idle or rev on light load or in the workshop quite well even with only 6/7 cylinders firing. If you know what you're doing you can pull off individual plugleads whilst running to identify bad leads/plugs/coils. I can do safely, this but I advise EXTREME caution to anyone who does not understand the issues/risks.

Sorry if I'm sceptical, I used to work for a major global premium manufacturer (powertrain enginnering) and just don't trust most "mechanics" aka fitters....

One of the ignition coils is probably failing. It isn't uncommon for that to happen. It usually only shows up under load. The top of the inlet manifold needs to come off to access the coils, this also makes lead replacement much easier. Purchase only genuine branded coils, ACA chinese cheapies are garbage. Someone on the forum worked out what other vehicles ran these coils, I can't remember just now.

Don't any of these guys use a laptop with some proper diag software? When I had some issues I just plugged in and went for a drive, logged the data and checked it all out later to see if I could see an issue.
Found the two faults this way - crank angle sensor (died once warm) and 02 sensors (confirmed by looking at read outs and loop control).
PCMScan is a good one if you want to suggest something to them...

The mechanics were just hopeless. The last guy assured me that the car was fine as there were no codes on his reader.
I took him for a drive and said does this feel as if it is running ok?
He then wanted to replace the leads and experiment more at my expense so I took it off them and bought a compression tester. Pressures are around 130 in all except cylinder 4 where it is 100 ish.
Thinking that it is a blown head gasket now and the chirping sound may be the leak.
Based on this should I pull the motor down to look at it or is there anything else (cheap) I have missed.
I might have a crack at this myself as I got quoted 3 grand roughly to do this and I am not going to waste that much money on a car that will in all likelihood have something else major go wrong with it. Before I take the plunge I just want to make sure this is the way to go although the compression figures are pretty damning.

I don't really have much to offer, apart from if it had never had plugs changed previously at 142 (or even 100k with the replacement engine) it probably needed them. I pulled ours at 102k and they were shot. (service interval on them is 120)

I've just pulled the heads off ours (water leak to the outside). Its not too bad a job, apart from the fact that the head bolts are incredibly tight.

if you do give it a go, make sure you have a decent 6pt socket, preferably with the lead ground off to make sure they cant slip. You will also need (or I did) some sort of tube on the end of your breaker bar.

good luck!