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· '93 White LWB, 235/85R16, 2" OME, Bottorf bumper,
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Discussion Starter · #1 ·
This is really a continuation of my running-like-crap-on-the-highway saga, but the plugs are the ONLY thing I haven't changed in the last 20k miles. I checked all connections, and what baffles me is that it starts up just fine, and although at the tailpipe it SOUNDS like it's missing on one cyl, when I move to the engine bay, it sounds smooth. I'm taking the exhaust note as a false indicator.

Revs freely at idle, but it's beginning to "miss" at other lower speeds on acceleration, and DEFINITELY at 60-65 at light throttle. When I move up to near 70 mph, it seems to clear out, and also if I downshift and let the engine rev @ 2500 and above. Runs cleanly then.

Because of the smooth-ish idle, I have NOT put a timing light on each plug wire yet. The one thing I HAVEN'T done in the last 20k miles is CHANGE the plugs. When I checked 20k miles ago, each was burning picture-perfect cleanly.

But if one (or more) has now opened up a gap that is excessive, MIGHT that cause a mis-fire @ low rpm?

At 169k miles, is the OEM-spec plug still the best, or is there a preferred alternate?
 

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I run NGK plugs, they work well. I've tried AutoLight from auto zone, those were a nice cheap plug. DONT use a Bosh performance plugs, I had bad misfires, ran like crap. The Dizy and coil need to be upgraded for performance plugs. Have you looked into the E3 diamond fire? Those are definitely will be my next purchase!
 

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I've always had good luck with the Bosch Copper plugs, they are what everyone suggest for our old BMW and 928S, so I continued with them in the Rover as well. IN the Bikes I've always run NGK. Champion is OEM for the Rover, so they are probably a decent choice, but I've always had an aversion to Champion plugs, primarily propagated by a midget sprint engine (2 stoke) shop I worked at years ago. Saw a god number of motors with holed pistons running Champion plugs. We shipped the engines with NGK and would receive them back blown with Champions, but in reality it was probably the specific application not the plug manufacturer.
 

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i ran bosch platinums then switched to champion coppers. didnt see a change but i was also experementing with a few things at the time. i think i will go with NGK's or the like next time. Also i have the Pertronix ignition in there now.
 

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Plugs for the 4.2 motor

I'm on my fourth Classic, now a '93 LWB with the 4.2. My first 4.2, and it runs like a jewel. Not gonna touch it 'till it burps. The 3.9s don't lie at the tailpipe tho. If you hear a miss there, it's going to fail at higher rpms as well, but harder to recognize. Champions were famous for pressure failures in the past, so I don't use them. A local RR engine guru told me to use copper cores w/normal sized tips that were OEM type for the older cars. Best not to fool with the platinums/etc which usually miss at idle when new...and actually get better after they 'burn in'. The conventional plugs are the best to use unless you are flat track racing your Classic. Do not mess with the heat range or plug length. This stuff on different forums...but you have to pay attention to get decent performance and better mileage. These tend to be the lower priced plugs, and have found NGK and the Autolite to go farther, better than others. Bosch used to be better 10+ years back. If they are uneven still after a new set, be sure to chk the wires first, and run 'em 50 miles before you do the exhaust pipe test to allow them to build heat for awhile.
RR saying:buttrock::buttrock: "If it ain't broke, don't fix it" is a dang good mantra to remember when fooling with RR motors. Every time you stick a wrench in 'there' you stand the chance of breaking something else. Many times, the 'something else' costs 6 times what you came to fix. DON'T tempt fate!!!
 

· '93 White LWB, 235/85R16, 2" OME, Bottorf bumper,
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295 Posts
Discussion Starter · #10 ·
Follow-up:

Purrs like a kitten at all rpm's with the Autolites! The problem was definitely the plugs, although I can't say for sure if it was just the plug GAP or not, since they were ALL over-gapped, and I changed them all at one time, gapped correctly.

And another strange thing happened: My constant idle-speed clacking noise from what I deduced was a collapsing lifter has strangely gone silent.....
 
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