Jeeps dont seem to like high RPM's

[Dave in Eugene]

102" plus a 6" spring. That's 9 feet. Used to be into that with my buds back in the '70s and that was and is the best way to get performance. Plus we were in the heart of the Oregon Dunes National Recreation Area and to offroad there you were supposed to have a flag (that was about the only rule back in the day). A full size CB whip was just about right and about every store in town had the little orange triangle flags to slip over the top. My sand dune rig was a 1962 Scout. 152 slant 4, 3 speed and twinstick dropbox. Guess you had to call it a dune crawler because it sure wasn't fast. The manners of a stock XJ remind me a lot of the old Scout. Quiet and smooth running, low to the ground and stable, but capable of much more than one would think at first glance. The XJ has a couple nice things that the Scout didn't. My personal favorite would have to be electric windshield wipers.

 

[outlander]

There isnt one on the older renix stuff. I had my parts rig to 6300 rpm

That's what I was thinking.....
Good thing I didn't go out side like an idiot that believes everything he sees on the internet and hold it to the floor!!

 

[5-90]

That's OK - this is one case where I'd expect you'd figure it out pretty quick.

That Diesel comparison is pretty close - whoever came up with that idea, good job! The difference is that the Diesel runs a much higher compression (2-3x Otto cycle, gasoline-fuelled engines) so the individual shocks are MUCH stronger, and the stresses on the reciprocating assembly are correspondingly greater.

With the AMC242, we have low compression (8.7:1 - 8.9:1,) but we have a much longer crankshaft, which gives a greater lever arm for individual "hits."

I'd not know if RENIX has a rev limiter or not, tho - like I said, I've never really had mine ABOVE the redline - I touch it probably twice a year, just to make sure everything's still balanced well...

5-90

 

[Dvipercop]

actually it was the really long metal one from radio shack. what's that like 6' or longer??? i don't remember. i did think it looked weird at first, but being able to talk to truckers 6 miles ahead makes for a ticket free trip. LOL

i'll try and see if i can find some of the pics.

PS: believe it or not, but in the 70's and 80's you could get corvettes with optional CB's from the factory.

Hahahaha!!! You've gotta dig up some pics of that! That just goes to show that someone at the factory was thinking ahead for those ticketless freeway speed runs...

 

[casm]

I was gonna say, my speedo max's out at like 100, but the governor kicks in at about 95mph....

Interesting - I wonder if the number's year- or package-dependent. I don't remember ever hitting the limiter in my old 2001 Sport, but the current XJ (2000 Limited) cuts fuel at 110mph until you slow back down to 90mph. And it's a *sudden* cutoff, too - when it happened, apart from the sound of something going 'boom' I really thought I'd broken something, likely the fuel pump. And this was in early August in the middle of the Mojave desert; that was the last and only time I decided to see what it would max out at Incidentally, that 110mph figure was obtained from my GPS. Speedo was off the dial at that point, so I'm going with what Garmin tells me here.

As an aside, mine won't let me engage the cruise control above 85mph either. Not that I usually drive that fast (70mph urban freeways, 80mph open roads) but, again, it was my one and only record attempt.

 

[summitlt]

That's OK - this is one case where I'd expect you'd figure it out pretty quick.

That Diesel comparison is pretty close - whoever came up with that idea, good job! The difference is that the Diesel runs a much higher compression (2-3x Otto cycle, gasoline-fuelled engines) so the individual shocks are MUCH stronger, and the stresses on the reciprocating assembly are correspondingly greater.

With the AMC242, we have low compression (8.7:1 - 8.9:1,) but we have a much longer crankshaft, which gives a greater lever arm for individual "hits."

I'd not know if RENIX has a rev limiter or not, tho - like I said, I've never really had mine ABOVE the redline - I touch it probably twice a year, just to make sure everything's still balanced well...

5-90

Renix definatly doesnt have a rev limiter, like said, I got 6300rpm with my parts rig, it wasnt limited, it just sounded bad. I also tried a neutral drop from that rpm, numerous times. Everything held up (wow?!)

Neutral > Pedal to floor > drive > *buring tires > go!

Tried it in 4 wheel drive too, it didnt liek that too much but nothing was broken. Pretty strong rig.

 

[majic_tech]

If ya wanna rap the hell out of a 4x4, get a grand with the 4.7L they will do it all day long

 

[BradJ]

My '93 4.0L auto sees 5k on a regular basis (171,000 miles so far). I've put Mobil syn in it since purchase at 95K. There is definitely a rev limiter at 5200. It's not as smooth as an aftermarket, but it'll hover right at 5200. I never brought it that high with the original exhaust (doesn't make much power above 4k). With a full 2.5" exhaust (header to tailpipe) it'll pull hard all the way to redline. I've also had it over 100mph quite a few times (in a straight line, of course with good tires, brakes, etc.) I wouldn't recommend those speeds with stock suspension though (soft springs and shocks).

Has a slight valve seal leak when sitting for a while. Otherwise I can run it at 3500 for 3 hrs staight and use no oil.

I can't seem to kill it, so maybe it's time for a supercharger If only all cars were this reliable...

 

[Mudderoy]

Limiter kicks in at 120 huh? Had no idea it'd do 120 and I'm not sure I'd want to be along for the ride.

I am amazed at the XJ. It is very smooth (stock setup) at 100+ My speedo stops at 100 mph, and I know I've continued accelerating above that, just not sure how much.

I've only done 100 once after the 4.5" lift and 32" tires. It will still get there, but I need an SYE.

 

[DougJ]

Holy Dead thread revival Batman!

This thread started around Christmas '05 so...

Merry Christmas from Iraq! :us:

Doug

 

[srmitchell]

Old thread, but a good one.

Anyone know how the rev limited works?

I imagine it cuts spark.

 

[xj88superjeep]

ASD relay kicks in, I imagine!

 

[Fastdemise]

MERRY CHRISTMAS!!! I know the 01 XJ Sport I drive has the limiter at 5200 and I've driven 120 in it down in I-95 with my buddy in his Suzuki TL-1000R watching his speedo. Baby can move when she wants to and the engine wanted to keep pulling but seeing how my tires from the factory were only rated at speeds up to 105-108 (depending on the tire) I hit 120 and slowed down. ^_^ Happy Holidays. From one crazy idiot to another

 

[Mr_Random]

Renix TBI 2.5, ran that sucker (sipper) at 4200 on more than a couple trips to phoenix, it's VERY undersquare compared to the 4.0, and doesn't have the same harmonic problems, so pulling into high RPM's is no trouble... fastest I went was somewhere well above 85, my needle went all the way down to the stop then started bouncing around. Got passed by a cop while doing this, that was scary... But managed 27MPG on that trip. Note: everything was completely stock, 22 years old, badly maintained by PO's, and basically on its' last leg...

Now I'm swapping in a rebuilt (overbored, dished forged aluminum pistons, higher compression, fresh cam and head) engine, upgrading to MPI, lifted ~3", 30" tires, stiffer suspension with better shocks... We'll see how it likes running at speed, and what mileage I get from it. Hoping to get back to the mileage I had a year ago before I killed the engine (cracked manifold, blew piston rings on #2, rear main blowing oil). I'm expecting at least 20 more horsies from everything added, not much more torque though (torque doesn't benefit much from added air flow or a change in fuel delivery, only thing helping it here is added compression).

Yes, dead thread... but I like the info on here.

Oh, and my (totalled, not my fault...) 97 3.9L 2wd 5spd long bed dakota sport didn't hit any speed limiter until 120... I took it there once, and near there one other time... didn't feel too bad to be honest. That thing was light and quick, I could chirp the tires without trying, and often lost the tail end around corners even at low speeds, it got better mileage and felt better altogether when loaded.

 

[8Mud]

I've never found the rev limiter on my 88 and live in autobahn country (no speed limits). Maybe the export models don't have a limiter?
Mine also runs smooth to 6000 or so ??? Though that wasn't always the case. My O2 sensor was acting like a rev limiter for awhile (until I replaced it) and would pretty much shut it down over 3500 RPM.
Heli core plug wires (non resistive type) with a stock resistor coil to cap wire and a fresh/clean distributor cap, may make a difference.
That high RPM shaking could be as simple as spark breakdown and is fairly typical for borderline ignition parts.
The shaking may have nothing to do with your motor, some drive line parts shake at odd RPM's like front U-Joints.
I drive mine daily for short distances at 100 MPH (my speedo goes up to 115) with only a thumb in the steering wheel, never noticed any shaking in mine.
One last reason could be a vacuum leak, they can mess with your motor balance also, some cylinders can run a bit lean and others a bit rich, with can't be good if you want a smooth running motor.
Though I have to admit the vast majority of my driving is below 3500 RPM, on 30 inch tires.
Sorry thought I saw 88 the first time I read your post, I guess distributor and plugs wires aren't going to help you much in your 98, but may help someone else.

 

[92xjsp]

Mine seems to do fine in the 4's - in fact, one reason why I bought this one over the other used XJs I was looking at was that this one seemed to be more capable of handling highway passing situations. In my test drives I found that it has pretty good pick-up from 40 to 70, if you push the pedal to the floor. It gets noticeably louder, but it's a good engine roar sound, nothing sounds like its coming loose. It just sounds like it's guzzling about a gallon of gasoline per mile. Thus, I don't use it much, but if I need to pass somebody on a 2-lane road or get onto the interstate in heavy traffic, I'll stomp on it.

 

[xj88superjeep]

My 97 never stops pulling!! Smooth all the way to the redline in every gear! I can accelerate from any speed and have been able to pass any car on the road so far. (even a brand new Charger that mistook me for a soccer mom, I guess, LOL, I pulled away from him at will when he decided to play, and we were on a freeway where he had his own lane!)... I would easily push it up to 100, but no need to do much more than that... (unless you are neutering a Charger!)

 

[Sherman_thetank]

So even my 89 has a rev limiter?

Me thinks me should go out and fire her up and answer me own question.....

My 88 does in a weird way, when you get to about 5500 it starts to stall and sputter and as your laughing hysterically you look out the window and watch all of your $2 a gallon float past you in a cloud of smoke......great for keeping bugs away though.:guitar:

 

[RichP]

I found out a few years ago that my 98 4.0, 5 speed, 3:07 gears with LT235's will do about 128 before the rev limiter kicks in. Got in a 15 or so car convoy one sunday morning on the north/south pa turnpike, exotics, MB's, Porsches, aston martin, making a high speed run down to philly, never dropped below 110 the whole way and not a single state trooper to be seen for the entire 70 some odd miles.

 

[themangeraaad]

Few years back I managed 115 in my 93 4.0 5-speed, 3.07's with 30x9.50's (stock except tires) measured with my garmin, slight downhill grade, Jeep FULLY loaded driving out to college. It was still pulling hard, felt like it could have easily made it to 125-130, but then I hit a pot hole and the full load/old suspension caused the Jeep to start rocking back and forth... and it didnt stop till I was down to 60mph.

Then got 3.5" BDS lift and 33x12.50s (backspaced to about 3-4" out on either side, still stock engine and drivetrain, gotta replace the 3.07s...) My buddy pulled along side of me in his mustang, I got to about 100 uphill according to his speedo. Gotta say, after doing the lift/tires it felt MUCH more stable than stock, even beating around on anything-but-straight back roads

Also love that I was still pulling off 19 (plus or minus a couple) MPG highway, as when i filled up and compared my odometer to gallons used, it worked out to be 16-17mpg before compensating tire tire size which should put it up to around 19 (thats for about 1/2 city 1/2 highway) and another time did 100 miles on a bit over 5 gallons of gas (combined city/highway, mostly highway). Just left it in 4th on the highway and let it cruise at 2.5-3k RPM's, doing 80-85mph the whole way. Cant complain about that mileage in a lifted, tires, non-regeared refridgerator box on wheels