Backfiring / Misfiring problem on 4.6V8 P38

Hi all. My RR P38 has recently, and quite suddenly within the space of a week, developed a backfiring / mis fire problem. I think it's more a back fire than a misfire.....as you hear the noise of it back though to the large air scruber filter box. So firstly, am I correct in thinking it's a back fire, not misfire???

In any event, the firing problem seems to be mildly present even on tick-over.....but the backfiring becomes more serious at a certain throttle rev range?...and is enough to make the vehicle judder. The problem came to light last week on a very damp and wet day (remember all the rain we'd been having!!) and as I was accelerating away (doing a rolling start off blocks on the M6 TOLL plaza...as you do with a V8!!!!!!) it started playing up.

I took it easy and limped home, and I've since checked usual things like plugs and plug leads for secureness or dampness, and that all viseable electrical connections look ok, and that all viseable 'air intake' related hozes and pipework look ok. Which they all visually look ok and secure. I've had some friends tell me that the symptoms sound like something really serious and expensive like maybes a burnt exhaust valve or broken air-meter sensors etc. Has anyone out there come across similar probs, and / or can offer any advice.

Cheers, John-o.

SIII 88 County RR Classic Vogue RR P38 4.6

Reply to
John.gjg
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Without hearing it, I'd say it's ignition related. Is it Gems or Thor (Motronic)? Best bet is to get it on an analyser if Gems, or Testbook/Autologic/Rovacom if Motronic and milk the ecu for misfire detection fault codes. There is a little history of the Thor versions eating coil packs, my DII did it and I've replaced a good few for others as well, but never had to replace a coil pack on a Gems as yet. Badger.

Reply to
Badger

Hi, Thanks for the info. Off hand I think it's the Thor type - but couldn't be sure of the top of my head. I'd better get it booked in at my local LR Services garage then for them hook it up to a PC. Cheers for the info! John.

Badger wrote:

Reply to
John.gjg

Another thing to consider if it's the thor type - they use spark plugs with a different ceramic insulator diameter (smaller) and if you fit the wrong plugs at any point it stretches the insulator boot on the end of the lead, rendering them useless at keeping moisture etc out of the end fittings, especially if you later revert to the correct thin-body platinum plugs. The thor's motronic management system is extremely complex in the manner in which it provides misfore detection and it doesn't respond well to the fitting of plugs other than platinum, or irridium for lpg use. If testbook etc shows up multiple misfires on any two cylinders that share opposite ends of a single coil (1&6, 8&5, 4&7, 3&2) then it most likely points to a fault within that coil pack. The packs are around £40each from landrover and there are two of them, but the upper half of the inlet manifold has to be removed to replace them! Best to replace the leads at the same time, around £90 for the set!! The lead end fittings are not std and as far as I know there are no decent quality aftermarket ones available... cue Beamends?

Badger.

Reply to
Badger

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