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Tachometer Readings

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Tachometer Readings

Post  Scarytallman on 6/26/2014, 1:48 pm

Maybe a dumb question but... Has any one had the issue where their tach reads about 1000 rpms less than you would expect? If i believe my tach, I apparently idle at 0 in Neutral, and i can access all my acceleration power at about 1500-2000 RPMs. Seems a bit odd to me. 95 YJ 4.0L 5 Speed
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Re: Tachometer Readings

Post  THOOPY3 on 6/26/2014, 2:39 pm

Well there's definitely something wrong with your tach if it's idling at 0 in neutral. Not sure what you mean by "acceleration power" but I don't shift my 2.5 much higher than 2000 rpm around town (unless say merging into fast oncoming traffic) or maybe 2500 rpm highway, or she's begging for mercy. That 4.0 should have plenty of grunt to get the job done I'd think.

Keep in mind that you have larger tires on your Jeep (31s if I remember correctly) and stock gearing (again if I remember correctly), and if the speedometer gear hasn't been changed your speedo is off by easily 10 percent over your actual speed. I can do 60 mph (actual speedo reading 55) on the highway in fifth and only tach out at 2000 because of my larger tires, stock gearing, and factory speedo gear, whereas with stock sized tires I'd probably be doing 2300 to 2500 rpm.

But again something is definitely wrong if your tach reads 0 in neutral. Something is loose/unplugged/frayed/not right somewhere.
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Re: Tachometer Readings

Post  Jake on 6/26/2014, 5:07 pm

Seconded. Though its not really relevant I feel the need to throw in that I do 70 at about 2k rpm with 33's.
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Re: Tachometer Readings

Post  Scarytallman on 6/26/2014, 6:29 pm

Ok I do about 75 at 2300 so nothing weird
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Re: Tachometer Readings

Post  THOOPY3 on 6/27/2014, 10:34 am

Is that 75 mph actual or 75 according to your speedometer? If that's 75 on your speedo that means you're actually doing anywhere from 80 to like 85 mph, and 2300 rpm seems waaaay too low for that. Even if it's 75 mph actual, that still seems too low to me. The thing would be such a dog I can't even imagine driving it on the highway, god forbid a hilly stretch. You must be in 4th until like 65-70 just to have (what I consider) power just to pass a Prius. Maybe that's just how it is with the 4.0/3.07s combo. If it was primarily a highway cruiser you'd be getting buku gas mileage though.

For me to do 75 mph actual I'm easily at 3000 rpm, which is why I don't frequently drive around at that speed. Hell I can hit very close to 3000 rpm in 4th doing 65 mph actual, and I'm under-geared just like you are. Jake's situation sounds a little more reasonable, because he's on 33s with 4.10s (I think), meaning he too is still slightly under-geared (if it's an automatic). If not then my understanding of the 4.0 is totally off.
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Re: Tachometer Readings

Post  Scarytallman on 6/27/2014, 10:41 am

oh its actually only around 2K RPM maybe less, checked today, and that 75 reading is the speedo no idea if its accurate. My jeep screams on the the highway... for a Jeep. I do alot of highway since i travel so much. On the way to Bangor I get about 18MPG+, but I just changed my dirty air filter so I am hoping it will be even better today when I go up. In low gear it still crawls with no gas pedal being pushed so it can still handle the woods. I do have to say it gets mighty floaty at the 85 MPH reading. It was a dog on the highway until all the the U-joints got replaced, now its a champ. The tach not working properly doesn't bother me because i can hear the engine fine. Its the speedo now that makes me worried because I don't want tickets.
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Re: Tachometer Readings

Post  Jake on 6/27/2014, 10:49 am

Speedo likely reads lower than your actual speed. Mine is 12% (calculated by odometer reading vs true distance on long trips) off with 33's vs stock 29(?).

Tach is definitely not acting normal for you, no idea what the cause could be but I'm sure some research would turn something up..
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Re: Tachometer Readings

Post  Scarytallman on 6/27/2014, 10:57 am

I think my GPS does speed. I'll have to find a flat spot since it is as the bird flies and see what i get in relation to my speedo. I didn't think Jeeps could do 80+ lol.
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Re: Tachometer Readings

Post  Jake on 6/27/2014, 11:20 am

If your suspension and steering is solid I don't see why not. I usually don't go any faster than 75 myself cause it starts making new noises at that speed, and I don't really feel the need to go faster. I do find myself casually doing 90 by accident when driving regular cars though lol.
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Re: Tachometer Readings

Post  Scarytallman on 6/27/2014, 11:33 am

lol yeah in my Subaru its hard not speed after being in the Jeep, its so quiet. As for my Jeep I have replaced so much the steering and suspension should be good to go lol
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Re: Tachometer Readings

Post  THOOPY3 on 6/27/2014, 11:36 am

They can move when they want to, just ask the dickhead dealer runner who couldn't outrun me in his new Audi on Route 2 a few years back doing 95 mph. The look on his face was priceless. That was before the lift and new tires, now I rarely do over 65 for both gas mileage and safety.

18 mpg is pretty good, and it's definitely because the gearing is the way it is. You're actually doing better than 18 mpg because you haven't been taking into account that the odometer is off, and that's quite impressive. On a typical 15ish gallon tank (gas gauge is fooked so I never really know where I'm at) my odometer reads roughly 235-245 miles if I push it, but my speedometer is about 10 percent off which means I've actually gone 260-270 miles. That's about 16 mpg on the odometer versus about 18 mpg actual, quite the large difference.
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Re: Tachometer Readings

Post  Andrew Miller on 7/4/2014, 12:59 am

With mine (33s and 3.07 gears) I can do 70 mph at just 1850 rpm, when i hit hyperspace between 70 and 75, she sits at about 2K. That is also when she is the most smooth, and that usually happens on a downhill or flat ground. Occasionally i hit 80 mph at about 2100 rpm, but i don't usually stay there for long, due to having knobby mud tires and everyone else' safety around me  Very Happy 

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Re: Tachometer Readings

Post  Jake on 7/5/2014, 8:17 pm

Another point of note is that most if not all mud tires have a speed rating of 75 mph. What exactly that means in terms of safety I'm not really sure though.
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Re: Tachometer Readings

Post  Scarytallman on 7/7/2014, 9:32 am

I should probably check the rating on mine. I didn't even think of a speed rating. I have BFG AT KO
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