My 2008 4.2SC has a misfire when under load -accelerating normally ,however is fine at tickover and goes past the misfire and clears when under heavy acceleration.There are no fault codes for engine ,the spark plugs are new and correct type ,i have tried another air flow meter ,tried fuel treatment to eliminate any chance of valve stick and am running it on Shell V Power.The only fault code which has appeared a couple of times U2023 Engine Torque Information and once P0500 Vehicle Speed Sensor .these may be being caused by the misfire or hopefully not by speed sensor failure in the transmission which is part of the mechatronic unit and not seperate.
When I bought the car I found that the engine oil was greatly overfilled - around 3.5 litres over ,the catalysts seem to ok but havent had a chance to emission check these yet.The vehicle runs ok when driven on light throttle .Has anybody had this problem or have any ideas? Range Rover Overfinch Vogue SE 4.2 Supercharged.

Hmmmm another interesting one !! Sorry that it is giving you problems though .

My first thought would be ignition related. Either that cam/crank shaft sensors or the coils. My suggestion is to check each coil for cabling, connector seated properly and the coils sitting tight on the plugs. Also take each coil of and check for any sign of a problem, cracks, damage, loose parts etc.

Second thought could be false air but that doesn't gel with good tickover and the heavy acceleration being OK. But it could be some false air coming in under partial load or just enough so it causes the misfire, although unlikely IMHO.

The recorded faults are unlikely to be causing the problem, they may be a result of it.

Also I suggest to check the lambda sensors although be carefull when pulling them out, the stainless steel is susceptable to galling and seizing !! I don't think it is those but it is something that you could check. Start with cabling and plugs.

Do you have an IID or Faultmate ?? If so, have a look at the live data and record it so you can post it here for others to have a look at as well.

Hope this helps. MY 2010 5.0 SC Galway green and sand interior!!
Have the Faultmate MSV2 Extreme to be tinkering with the settings etc. !!

Hi ,again ,yeh I think you may be on to something with the coils ,ive just this morning checked catalyst operation and CO levels on emissions machine at work and all showing ok at tickover and through the rev range .Im going to try and borrow a friends Snap On Scanner and check live data ,the only thing puzzled me a little was that on Jaguar V8 normally a misfire registers as a fault and ive not got any misfire faults - maybe as the coil hasnt completely broken down. Range Rover Overfinch Vogue SE 4.2 Supercharged.

Just back in house after an hour or so with my mate and Snap On Solus Scanner ,we have found some strange occasional patterns on No2 coil and when under heavy load No 5 coil as well ,neither were far enough out of spec to cause a fault code but cetainly enough to cause the slight misfire ,all other engine data looks good and the transmission speed sensor code has not returned so as you said its probably been caused by the misfire.Thanks again mate for your helpful suggestions ,it always helps to talk about faults with someone looking at the problem from outside. Range Rover Overfinch Vogue SE 4.2 Supercharged.