[RRLondon]

Steady 90mph in a RRC??? You're quite brave sir!

Same as above for mine too, runs arrow straight and completely calm at 90mph. It had the shakes at 60 to 70 mph when I bought it (the previous owner didn't go over 60 to avoid this) but sorted the problem and it's fine.

It's a consideration when we take it the the Alps through France, almost entirely two lane on major route and 130kmh with many HGV on inside lane. Either you have to dodge in and out into that lane to let faster vehicles pass you or match them. Generally, flow unimpeded is about 88mph (90mph speedo and 88mph gps) so we just fit in with that.
Fortunately that's almost right at engine torque peak for my 3.9 at which it feels relaxed. I honestly thought that elevated speeds would severely take their toll on fuel consumption, but it's the most economical right there. Fuel light on when flat and level gives a repeatable 40 miles to get more, 50 and it'll be dry!

 

[RRLondon]

To add some further thoughts, check the wheel centres after a "cruising" journey for brake temperature. You'll ordinarily notice any hotter than another, I put the palm of my hand on the wheel face in the centre and they're mildly warm to give a rough and ready check.
But if you have an ir thermometer you can be a little more scientific in checking.

Also, I run 75/80 multigrade GL5 rated oil in the axle diff casings which seemed to offer a small improvement to my mileage.

 

[Adam G RRC_92]

I'm jealous of those numbers. @RRLondon, do you have stock suspension? 90 mph would feel risky. My steering has always felt light and squirrelly with the PO lift. Just tightened the steering box the other day, and installed a new damper. Haven't had it on the highway yet. Might feel better.

So, I pulled all spark plugs (service manual says to do this to check for leaky injectors too), and I've included a pic of each of the 8. I don't think they look awful, but a few look to be aging... or even ashed. 8933 pic looks pretty ashy. I also am not getting any Service Engine light, so I feel like whatever is gonig on is (hopefully) a tuning thing... not a part going bad?

I looked around the injectors but don't really pick up any sort of leak. Didn't smell anything at cold start today.

 

[LanceL]

My RRC is steadier at 90MPh than my 2017 Wrangler is.... with the same BFG K02 tires!

I can see that to be honest, I drove my brother-in-law's '07 rubicon (which was bone stock) on I-70 in Colorado (75-80mph) and thought "man my rover is more stable that this, and it doesn't even have sway bars! ('89 I believe was the last year that didn't have them)

My biggest fear is evasive maneuvers (bit top heavy these things!). I always leave a big gap to give more time to react, and I drive pretty defensively (under the assumption that everyone around me is always about to do something inescapably stupid) but I still feel I have a better chance of seeing and avoiding something without tumbling to my death at 65mph than I would at 90.

What I've noticed at higher speed on the freeway as well is NOISE. Over 75mph the roar of the wind (despite not having any door seal leaks) and the engine noise at 2700+ rpm is too just loud for comfortable conversation. At 65 it's much more calm. I was considering putting dynamat around the whole cabin when I re-do the carpets, perhaps that will help somewhat. I don't think my tires are super noisy, and my exhaust isn't overly loud, but the truck does just have a lot of ambient road noise the faster you go.

 

[LanceL]

Also sorry didn't mean to derail te conversation. Those plugs don't really look bad to me, maybe some ashy stuff on a couple and one is a bit black, but I don't think it's significant. Have you tried JS5D's driving a known fixed distance on google maps suggestion? I know it seems silly, but it's a good test to at least rule out a hinky odometer, you never know.

 

[RRLondon]

Yes, mine runs at std height suspension springs (red white rears to keep it level when loaded) but Bilstein dampers.

Also with larger tires, Michelin Latitude Cross that are very good at speed. Steering self centres well and will effectively run straight with hands off at any speed.

Plugs all don't look bad, a little variable from one to another but not suspiciously rich for any single one. Are they NGK 5 rated?

Mine for fuelling setup is 3.9 litre all std for components and ignition at 6 BTDC.

But, I have got the only non std setting for the MAF gain with it running below the factory target. It was too rich and running about 14 to 16 mpg imperial when I got it and wouldn't improve.
I've formed the opinion that my injectors are possibly not as accurate as originally they were, now at 160,000 miles, and working on that basis I've pulled the reference voltage downward.
I've got the emmisions from testing to see where I've gone, and it's much more "on point" for torque now, and run about 10,000 miles at this mixture setting.
Reason I've asked about plug # is that I also moved (from 5) to a 6 heat range to keep plug temperature from being compromised.
It may be the case with yours that you'd have to consider a similar route to in effect deliver the mixture Tornado assume you will get.

Lower gain voltage will run the whole map leaner as it offsets the MAF report to ECU as far as I can determine from adjustment.

 

[Adam G RRC_92]

Here's what's in there: https://www.amazon.com/NGK-BPR5EY-V-Power-Spark-Plug/dp/B000A8MYNI NGK-R.

Lower gain voltage: Do you mean from the MAF? You can adjust that? And, the Tornado requires a specific mix?

I'm interested in this because I don't have error codes at all, so I feel like the performance chip has some requirements... and maybe those need to be checked!

 

[RRLondon]

Lower gain voltage, yes for the MAF. Instead of setting it at around 1.8v you'd choose to go lower.

The Tornado doesn't require specific setup voltage but will make the assumption that your installation hardware is delivering on target if set to std values, including the MAF response.

When the injectors are called by the ECU to open for specific time they will deliver correct fuelling IF they are working to original specification. If they are worn and delivering excess, then the rest of the system has no idea this has happened, it just uses too much fuel.
By offsetting the MAF gain voltage away from std, the ECU has report from MAF that Less Air is being consumed than is going through there, to which it matches with less fuel injection period, all for exactly the same engine speed. This makes the combustion leaner.
It's technically the wrong thing to do (that would be to verify/service/replace the injectors), but it will have the desired effect to test and refine the mixture. Also you can record and understand this non std setting so it can be removed if necessary.
In essence, it's a reasonable "calibration" of the system installed as it currently exists. It should be able to show you something of what it's burning by test and verification.

That plug heat range is important here in protection of the engine. A #6 rated NGK plug has a shorter heat transfer path that sheds tip temperature more easily than #5. If you inadvertently run (while adjustment of mixture) too lean, then the plug will give more margin before getting too hot which gives the risk of pre-ignition. To work with the mixture you'd need to pair with a plug change as prerequisite, it will also run at darker colour too and influence mixture decisions.

If you wanted to assess via this route, a start point of 1.35v gain and #6 plugs would be a median baseline to run it and see what consumption and plug colour you get.

 

[Adam G RRC_92]

I’d like to try changing the voltage. How is that done?

 

[RRLondon]

When you look at the MAF from the multi plug end, there's a circular boss near top right corner with the adjustment pot recessed inside there. They will usually have a anti tamper plug blocking the entrance if no one has previously adjusted which you'll need to remove.

You pull back the plug sheath and insert meter probe into back of socket to measure in situ. Switch on ignition but not start, then move the pot to give readout at setting you want.

There's a description with picture as to how you measure in the link I posted further back.

 

[Adam G RRC_92]

Curious, though, if the injectors were not performing to spec; the mix is off, we’d see evidence of that in the plug color right? So I just don’t want to focus on the wrong piece. It certainly seems this could be an issue as the injectors seem to be original. Could I also run a dose of fuel injector cleaner?

One other thing. This may be an oversimplification, but recently I had my plug 1 magnacore cable off and forgot to put it back on. Car ran, just sluggish. No check engine came on. Gas mileage was like 2 mpg before I realized what was happening.

Would there be any likelihood that I have a bad spark plug in another bay that just isn’t firing and I’m not getting any sensor reading?

 

[JS5D]

In my younger years I mainly played with crappy 4 cyl cars (Europe). On a 4 cylinder car you know when one piston is not firing. On a V8 less so. Possibly you have a missing cyl dt wear/failure in your ignition system. You would think your system would pick that up, but then it is probably quite primitive still.

Regarding adjustment to the MAF, this could help to get things more inline, but in closed loop does the engine management not tune to the O2 sensor signal? So the fuel map would be AFR values based on rpm and load and then a correction table is applied to vary inject pulse to match the O2 signal.

Are the O2 sensors wideband in these?

I admit I know very little about this system, I converted my 83 carb to Throttle Body Injection and know A LOT about that!

 

[RRLondon]

Your pictures of all plugs don't show any that appear not to be firing. But an easy check, start from cold and run about 30 secs, switch off and feel each exhaust port manifold right by the head. It'll tell you straight away (with a cold one if there's a cylinder out) and you can then trace any problem.

 

[Adam G RRC_92]

I don’t know about the O2 sensor. There are 2 heated sensors before the cats.

 

[RRLondon]

Regarding adjustment to the MAF, this could help to get things more inline, but in closed loop does the engine management not tune to the O2 sensor signal? So the fuel map would be AFR values based on rpm and load and then a

As I understand it the running is open loop during warmup (not sure of temp threshold it switches in control) also open loop at wide open throttle and anything above 3,400 rpm.

Without gas analysis it's real suck it and see method, hence recording the MAF start point voltages to enable return to now at least.

How tight the closed loop control is I can't find referenced other than casual 1 1/2 times O2 sensor boundary would bring on engine check light. Trying to understand exactly what that would mean in a practical sense, also the resolution scale of the closed loop logic.

 

[RRLondon]

An add on thought, to check the TPS for output (I forget who has replaced them on forum) as if the TPS was to flag wide open throttle the ECU could possibly be running open loop continuously, but with MAF readings giving absolute mixture.

Something doesn't add up here though, with plug colour, no code error in regard to check light, but still using that much fuel, seem to offer conflicting evidence.

 

[Adam G RRC_92]

I think first I’ll do a tripometer test, and check the hubs for brake heat. I agree conflicting evidence. I’m stumped. But she glides super easy and the brakes were recently rebuilt. I checked the brake switch and cruise brake switch for correct pressure. All good.

 

[Adam G RRC_92]

tripometer was checked and looks good. Hub temps after 5 mile drive are fine. temp on exhaust manifold at 8 plugs seems consisitent. Maybe the 7 and 8 were less hot. Not cold, but maybe 20-30 degrees cooler.

So, at this point, it would seem that the air/fuel mix is ok based on the spark plug visual. Spark plugs ok suggest that the MAF/injector/O2 set up closed loop is all working ok, as the Service Engine light doesn't seem to have any sensor errors. The engine is happy, it would seem.

There was a time not long ago that, while driving, I noticed that somewhere around 35mph it was hiccuping, in a sort of rhythmic pattern. Could that suggest a subtle misfire that's not really detectable? Maybe my thought is, "would a full engine tune up: new spark plugs, leads, etc be worth seeing if it makes a difference?"

One thing I wanted to add, this late, but worth noting... the Magnaflow Exhaust seems grumbley... and maybe loud for what I'd expect. Is that normal? Would the exhaust cause an mpg issue after the sensors?

 

[Adam G RRC_92]

Any concern/issue going with a #6 spark in my current situation (pre-MAF adjust?). I an easily replace all 8 to cross a "tune up" off the list.

 

[RRLondon]

#6 plugs aren't going to give a problem at all if you want to change them as part of diagnosis/service routine. I don't use the V electrodes just the BPR6ES type (check that spec for your engine) and gapped at their absolute minimum for specified settings.
What the difference is between the 5 & 6 is that the 6 will tolerate more combustion temperature if you run it leaner, it won't actually change much if you change nothing else. It's a good plug choice to run these on generally though.

One thing I wanted to add, this late, but worth noting... the Magnaflow Exhaust seems grumbley... and maybe loud for what I'd expect. Is that normal? Would the exhaust cause an mpg issue after the sensors?

Now that's interesting! Magnaflow make some very good components and this isn't aimed at criticising them. But I don't believe the general market philosophy for these engines in some of the design choices.

They really "like" ( strange way to describe mechanical devices) specifically constrained tail pipe sections, too little attention in this area (big and low restriction) significantly hollows out the low rpm torque curve, which ultimately results in running at normal speeds with wider throttle opening to maintain power output. They work well with a big "resonator" mid vehicle plus, a decent silencer right at the far end of any following system.

Have you any detail of the pipes fitted?