How many of us walk into a motor factor and asked for a set of plugs to suit a TR7 or a 1985 Range Rover (I have to for the V8), and walk away with what we're given? I did this last year.
Last month I had some problems with the engine stuttering under acceleration at low revs in 4th or 5th gear but no pinking involved. I cleaned up the plugs (NGK BP5RES) which helped a bit but there was still some hesitation on an engine which has always been immensely flexible and tractible. The plugs looked a bit worn so thought I'd treat myself to a new set and had a look over the net. I came across this.
http://www.ngkpartfinder.co.uk/cars_commercial.php
It recommends BP5E for carb'd Range Rovers & SD1's before they went to fuel injection which take BPR6E. Anyway, I found a set of these on the net for about a third of the price in Halfords (who were out of stock), gapped them and after fitting all was well again.
It could be down to the change to BP5E plugs or just fresh clean plugs anyway. It worked for me.
Adam
TR7 V8 DHC Jaguar Solent Blue. 9.35cr Range Rover V8, Holley 390cfm, JWR Dual Port, 214 Cam, Lumention, Tubular Manifolds, Single Pipe Exh, 3.08 Rear, 200lb Spax & PolyBushes, Anti- Dive, Granada Vented Discs & Calipers, Braided Hoses, 4 Speed Rear Cylinders, Uprated Master Cylinder & Servo, AT 5 Spokes and Cruise Lights. No Door Stickers. Mine since July 1986, V8 from 1991