Spark Plugs

This has spun out of a club bulletin board discussion, seems an
easy question but I have a few conflicting answers - Badger, your
advice seems good but contradicts the literature so I wanted to throw
this out to a.f.l to see what everyone thinks.

Simple question.

Land Rover Discovery 1997 V8 Auto 3.9 not LPG.
What spark plugs should it have?.

When I bought it it had champion NY11C

To replace them I bought 8 more but then, for reasons I won't
go into put in NKG BP5ES instead.

The car has issues anyway - running far too rich (sooty plugs)
and returning 11mpg driven gently down the motorway but those I am
dealing with.

So

What plugs should it have?

How important is the correct torque for the plugs or is
doing it by feel OK? NKG website says its vital.

And also - when I changed the leads and dizzy cap this weekend it wouldnt
start at all - traced it to a bad connection at the coil, corroded HT
lead 'socket'. Its now going again but it worth putting in a new coil
too - will it help pep it up.

Performance wise, turning onto a slight hill (1 in 20 ish) from a 10mph
turn it wont go into 3rd gear at 30mph - stays in second all the way up.
I don't think that's right.

Thoughts.

Badger - feel free to reitterate your advice.

"John Page" <[email protected]> wrote in message
news:[email protected]...
> This has spun out of a club bulletin board discussion, seems an
> easy question but I have a few conflicting answers - Badger, your
> advice seems good but contradicts the literature so I wanted to throw
> this out to a.f.l to see what everyone thinks.
>
> Simple question.
>
> Land Rover Discovery 1997 V8 Auto 3.9 not LPG.
> What spark plugs should it have?.

NGK BPR6ES, Chumpion RN9YCC, or platinum equivalent, or irridium if you feel
flush!

> When I bought it it had champion NY11C

Assuming it's the 9.35:1 compression ratio engine, N11Y's are too hot a
plug. Perfect for the 8.13:1 "soft" engines though. landrover fitted hotter
plugs to bring the emissions down ever so slightly, BUT there are too many
issues with 3.9 and larger engines having cracked blocks behind the liners
and liner dropping, some say caused by high combustion temp due to leaner
mixtures for economy, which is why I never fit hotter plugs than N9/BPR6 -
might not make an awful lot of difference, but it's piece of mind, IYSWIM.

> To replace them I bought 8 more but then, for reasons I won't
> go into put in NKG BP5ES instead.

Still slightly hot, but not as bad as N11's.

> The car has issues anyway - running far too rich (sooty plugs)
> and returning 11mpg driven gently down the motorway but those I am
> dealing with.

Done the coolant temp sensor yet, John?

> So
>
> What plugs should it have?
>
> How important is the correct torque for the plugs or is
> doing it by feel OK? NKG website says its vital.

It would! Tight enough not to work loose, but not too tight that you risk
stripping the ally thread out of the head. Most people do it by feel, but
the feel is usually based on probably years of experience.

> And also - when I changed the leads and dizzy cap this weekend it wouldnt
> start at all - traced it to a bad connection at the coil, corroded HT
> lead 'socket'. Its now going again but it worth putting in a new coil
> too - will it help pep it up.

Won't necessarily pep it up, but it eliminates another potential problem.

> Performance wise, turning onto a slight hill (1 in 20 ish) from a 10mph
> turn it wont go into 3rd gear at 30mph - stays in second all the way up.
> I don't think that's right.

Kickdown cable adjustment too tight??

> Badger - feel free to reitterate your advice.

Ta, I did.

Badger.