Having a bit of bother with the 4.2 V8 in my '93 Classic LSE.

It seems to only be running on 6 or possibly 7 cylinders. It's underpowered compared to normal, won't go above 70 on the motorway, vibrates badly, and only returned 10mpg over the last tank of fuel (usually returns 13-14mpg when running fine). Sounds like a Subaru at the moment...

I've replaced the leads, dizzy cap and rotor arm, but to no avail. The plugs are only a couple of thousand miles old.

Any ideas?

mileage, genuine arm and cap, plug make/gap ?

wheel bearings, wheel balance, steering damper, cv joints, props ?

156000 miles, NGK plugs, unsure what they're gapped to but were running fine when I fitted them.

Arm is Britpart, cap is unknown make. Problem was occuring before I fitted the new parts.

Any coolant loss?

VogueLSE4.2 said:

156000 miles, NGK plugs, unsure what they're gapped to but were running fine when I fitted them.

Arm is Britpart, cap is unknown make. Problem was occuring before I fitted the new parts.

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cam shaft last changed ? I only found out how easily they wear out after buying one with a bald cam

West Slope Rover said:

Any coolant loss?

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It loses a tiny amount externally, but I can see where that's coming from so not concerned it may be head gasket.

Dr_evil said:

cam shaft last changed ? I only found out how easily they wear out after buying one with a bald cam

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As far as I'm aware the camshaft has never been replaced. Would this suddenly cause the problems I'm experiencing?

What would my options be for replacement - would be looking to replace with an upgraded item?

yes it would and 150k is a lot on a standard cam, they're meant to last about 80k


replace it with an upgraded one then if thats what you want

VogueLSE4.2 said:

It loses a tiny amount externally, but I can see where that's coming from so not concerned it may be head gasket.

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Just because you can see one source of coolant loss doesn't mean that there is not another. How often do you top off the coolant and how much?

Right then, rather than worrying about worn cam shafts and fitting better ones, lets go back to basics! Yes the cam will be worn at 156000 miles but you should still be running on all 8 cylinders.

First things first I would be eliminating the simple things. If its running on 6 or possibly 7 cylinders then a good way to find out which cylinder(s) is/aren't running, is to pull an HT lead off a spark plug, then start the engine. If the problem gets worse, the one you just pulled is okay. If the running doesn't change, you've just found a cylinder that isn't firing. Repeat this for all 8 and you might come across the cylinder(s) that aren't firing.

As Dr Evil mentioned the rotor arm and distributor cap, you may have replaced them with new, but if you do a search online there are a reason people say use genuine ones. You might be surprised to find that a problem like this could, I'm not saying it definitely be, but it could be cured by using a genuine distributor cap & rotor arm.

Even if you already know and did so then its still worth mentioning when replacing the rotor arm to be careful as if it doesn't come off easily then if you force it off without pushing down on the reluctor you can pull the springs and weights out off. Then you have to go taking the distributor apart to put them back. Yet more hassle.

So as above find out which cylinders it isn't firing on! Once you've found out which ones aren't firing then its time to work out why. Good luck!

Distributor itself could be knackered - been coming across this more and more

After all they are all 20 years old.

RPi have some military ones for 75 quid - 80 with cap and arm.

we had same problems with my disco 1 - changed all parts except the dizzy

Finally changed the dizzy and ran as new

I'm a clown - the HT leads were on in the wrong order.

Thanks for all the help folks - much appreciated!

VogueLSE4.2 said:

I'm a clown - the HT leads were on in the wrong order.

Thanks for all the help folks - much appreciated!

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I bet your glad you didn't pull the cam out