4.6 Thor P38 MISSING! Running Lumpy

Range Rover is running REALLY badly!
Here is the actions I've taken so far (all factory parts):

1. New (expensive) spark plugs.

2. New MAF sensor

3. Took it to a Land Rover specialist to use his diagnostics computer. - This showed up that the Range Rover is not firing on cylinders 1, 5 & 7. (All on the same bank)
^^This lead me to believe that it may be a coil pack issue. But before replacing the coil packs, I thought I'd replace the leads, just to be sure.

4. Replaced the Leads.

5. Replaced both LAMBDA sensors.

STILL missing!!! After much time and money, I can't afford to spend much more!!

The Range Rover runs worst when idling, cold or hot (temp doesn't make a difference). When throttle is opened quickly, there is an OBVIOUS lack of power and delayed pick up.

Not really sure if it is a coil pack because it's missing on 3, 5 & 7 which doesn't correlate to one coil pack....?

Not overheating whatsoever, and all water/cooling system is perfect!

It doesn't seem that it can be anything to do with the fuel systems, because it's LPG'd (expensive, quality kit), and it runs EXACTLY the same on Pertol AND LPG!

PLEASE HELP CHAPS!!!

:Cry:

Have you done a compression test? Could be camshaft heavily worn.

Agree with Steve, do a compression test. It doesnt sound like coil pack if its missing only on one bank.
Similar problem with mine a couple of months ago. It turned out to be a blown HG (across cylinders 5&3). Mine lost no water & no overheat, just lumpy tickover & down on power. Same on petrol / LPG.

My 4.6 had similar symptoms and it was the coil packs at fault....

I'll do a compression test, but how would that tell me the condition of the camshaft? I'd be able to tell if any valves were burnt out, but surely if the camshaft was worn it wouldn't make much difference to the compression?

I'll do a compression test now.

iCharlieHolder said:

I'll do a compression test, but how would that tell me the condition of the camshaft? I'd be able to tell if any valves were burnt out, but surely if the camshaft was worn it wouldn't make much difference to the compression?

I'll do a compression test now.

Click to expand...

You'll lose oil pressure with a worn/broken camshaft. Compression test will tell you if its HG. Worth checking coil pack as well, and that the leads are correctly fitted.

When I recently had an issue like this it turned out to be a broken rocker shaft. The shaft snapped just before the rockers on #8 cylinder. Compression test showed #8 to be higher than the others. However this was all accompanied by additional mechanical noise which I mistook for being caused by the misfire.
So as others have suggested you might want to look at the valve train as well.
http://www.landyzone.co.uk/lz/f10/2001-4-6-thor-sudden-misfire-199887.html

Compression Test done!

Results:

Cylinders

8 - 170 psi 7 - 155 psi
6 - 170 psi 5 - 150 psi
4 - 170 psi 3 - 80 psi
2 - 175 psi 1 - 80 psi

Conclusion:
Seems like the HeadGasket has let go, across cylinders 1 & 3.

At least I know what the problem is now!!

Thanks Guys!

iCharlieHolder said:

Compression Test done!

Results:

Cylinders

8 - 170 psi 7 - 155 psi
6 - 170 psi 5 - 150 psi
4 - 170 psi 3 - 80 psi
2 - 175 psi 1 - 80 psi

Conclusion:
Seems like the HeadGasket has let go, across cylinders 1 & 3.

At least I know what the problem is now!!

Click to expand...

If you have the wherewithall then it would be a good idea to replace the camshaft at the same time as most of the work will be done doing the heads. I did my heads and 5,000 miles later had a constant missfire, changed coiles and checked injectors and fuel pump, nothing so decided to change the camshaft. It was very very badly worn with two lobes completely worn down so replaced it and followers and poped a new water pump on too as a precaution. Engine is now fabulous.
The extra work to do the camshaft is not a great deal only bit I hated was taking the sump off. But its all worth it. Camshaft and gaskets not a lot of money. So advise you do it. Oh and pop on a new timing chain (stiff) and sprockets, bet they are worn out - makes a big difference to how the engine runs.
My car 2000 year 4.6 p38 Thor Engine. Pic shows the engine being stripped down.

looks clean inside, stopover, must have been well looked after :5bhurray:

tufty said:

looks clean inside, stopover, must have been well looked after :5bhurray:

Click to expand...

Yes I think so. Apart from the camshaft the rest was in very good condition. I got the car with about 100,000 miles on it and was told that about 30,000 before the engine had been changed. Its done 165,000 now so a camshaft/ heads change at around 100,000ish isnt too bad to expect. I always change the engine oil and filter at 3,000 miles or close, maybe that has helped. This is a picture on the rebuild, nice recon heads and adjustable pushrods as the heads had to be skimmed to a point where the standard rods had too much pre-load. Managed to get a (rare) rocker set from a performance outfit in the UK which had only been used to run in a race engine, perfect. Camshaft was standard with new followers set to 55thou pre-load.
Have done a lot to this car, too much to list but new trans gearbox, prop shafts all U/Js, front 4pin diff, calipers, disks and complete overhaul of air suspension. Tie-rods and shocks. Modified exhaust + de-cat. new rads (all). Inside, new heater O rings, Hevac unit and updated TV to digital. Updated Sat/Nav and many other improvements in fridge/freezer for the ice to rear cocktail unit. Gun cabinets refurbd too. Its a nice touring car with plenty of urge when needed. Only downside is every panel has been vandelised (scratched) but have usd a retouch pen and in the right light you cant tel. Please someone change the law that gives me the right to stone to death these vandals.