RPM's Driving me crazy

[mickyjl13]

One of the things that took me a long time to figure out is that the engine fast idles until the computer is ready to let it stop fast idling. I guess this is to heat up the catalyst faster, for pollution control. Normally, you start a car, it fast idles, and if you put it in gear and go before it has idled down, it just kicks out of fast idle. Not so with my JL. If I start the thing and pull out a moment later, it fast idles all the way to the end of the street, fast idles at the stop sign, fast idles in the first turn, and doesn't really calm down until I've gone half a mile or so. It feels like it's pushing me when I don't want to be pushed, and the revs hang a long time.

I've found that I can avoid this weird behavior by starting it, and sitting there until it idles down on its own. Then when I pull out, I don't feel like I'm fighting it so much. It seems really stupid for it to behave this way, but what I'm describing here is definitely what my Jeep is doing, whether it's a bug or a feature. Whether it's what your Jeep is doing, who knows.

The other thing that's just an overall problem is rev hang. The revs on this thing behave strangely. Sometimes they hang a long time, sometimes they drop fast. I haven't been able to double clutch it or float it to downshift either. I like to practice shifting any vehicle without the clutch, so I know I can if the clutch takes a crap. Been there before. I drove 500 miles without a clutch one time. That was in a big truck, but still. So anyway, I'm not sure I could drive this without a clutch. I can up-shift without one, no problem, but downshifting, no. Pull it out, rev it, can't put it in. Can't match it. I think the rev hang thing is just messing with my manual syncrhonization mojo on this thing.

Oh, and saludos desde Virginia, amigo!

Hola Michael,

Gracias por responder. It is exactly as you write. All of it. I bought the Jeep out of nostalgia. Wanted a Jeep with no power windows or locks or no slip diffs nada. Plain good and simple Jeep. Easy to go topless and fun to drive. I even put a cigarette lighter on it. Beautiful looks, excellent riding and a soft clutch for my tennis knee.

Then... killed both supports of the soft tops in the back. And almost took the Jeep back to the dealer to get my money back because it would not start. Well sometimes it would but it took me a couple of days to figure out that if I don't press the clutch all the way... then came the recall notice for the clutch. At that point I was going crazy.

I took the jeep to a dealer and after three days they just added the new software and never took care of the soft top nor discussed the rev hanging etc. It made me very mad. The guy in charge left the dealer before I got there and nobody wanted to take responsibility for it. So I said fine. I will return the Jeep with the title to the dealer I bought the Jeep from. And I might do it. Sad.

Anyways... the idea was to buy the Jeep and bring it to my country. I can't now. Unless I find a fix for all the rev issues. Believe it or not, the Jeep dealer here would not sell a manual transmission one. Not permitted by the factory. Really stupid. But now that I see what is going on, it is better that they don't.

Saludos desde Bolivia señor!

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[omnitonic]

Anyways... the idea was to buy the Jeep and bring it to my country. I can't now. Unless I find a fix for all the rev issues.

How many miles do you have on it? These problems I have described are still present, but they have definitely gotten better as the Jeep broke in and got some miles on.

Believe it or not, the Jeep dealer here would not sell a manual transmission one. Not permitted by the factory. Really stupid. But now that I see what is going on, it is better that they don't.

Saludos desde Bolivia señor!

I love my 6-speed, but the 6-speed Jeeps have a lot of problems. The 3.45 gears are too tall. The clutch is very strange. I can see why the automatic is a lot more popular.

Hace muchos años que no conozco a boliviano ninguno. ¿Cómo es la vida cotidiana boliviana hoy en día?

 

[mickyjl13]

How many miles do you have on it? These problems I have described are still present, but they have definitely gotten better as the Jeep broke in and got some miles on.

I love my 6-speed, but the 6-speed Jeeps have a lot of problems. The 3.45 gears are too tall. The clutch is very strange. I can see why the automatic is a lot more popular.

Hace muchos años que no conozco a boliviano ninguno. ¿Cómo es la vida cotidiana boliviana hoy en día?

Hola Michael!

My Wrangler has 3k miles on it and being stored for a while. I should go back to the states in a month or so. I will decide what to do then.

Bolivia esta un poco complicado políticamente. Pero esperamos que los gobernantes se pongan de acuerdo para el bien de todos. Tiene muchas riqueza natural y la comida es muy sabrosa. Tienes que visitarnos cuando puedas. Un abrazo!

 

[R00STER]

I know everyone complains about the rev hang, but Jeep may have added it so drivers dont have to flutter the accelerator on upshifts and/ or heel-toe on down shifts. These are advanced techniques that are used by race car drivers to enhance performance, but they also can minimize wear and extend drivetrain components (if done correctly).

My late year JLUR never had the rev hang issue, but it could be possible that Jeep purposely included a rev hang on earlier models because they know most manual drivers won't rev match prior to shifting either up or down (even the ones who have driven manuals for 50+ years). Just a theory.

Also, even though it sounds cool, its not a good idea to shift gears without using the clutch unless you have sequential gearbox. The synchronizers are typically made of copper or some other soft alloy, so forcing them into position under the load of the engine is likely to cause premature failure. For the record, I am not flaming anyone who does this....it's your jeep run it how you want....I just don't want someone to do it thinking it sounds cool, without knowing the consequences of doing so.

 

[Lager]

I wonder if a pedal controller like a Pedal Monster or Pedal Commander could help with the rpms hanging? My JLU is an auto so I can't test this for the MT guys.

 

[omnitonic]

Also, even though it sounds cool, its not a good idea to shift gears without using the clutch unless you have sequential gearbox.

It's absolutely not a good idea. It will obliterate the synchros in short order if you aren't exactly in sync. With that said, I always try to get a grasp on this in any vehicle, so I'm shifting without harming the synchros. It's all about the timing. If you hear the synchros engaging, your timing isn't right.

That is just as true if you are shifting with a clutch, which is what I do 99.99% of the time on anything that doesn't have 18 wheels. If I hear the synchros kicking in, I have messed up. I aim to avoid engaging them far enough to hear them work, even when I am driving in the conventional, normal way like all the other four-wheelers.

 

[BuyHold]

These problems I have described are still present, but they have definitely gotten better as the Jeep broke in and got some miles on.

Similar experience here. The feel/interaction of the engine/transmission/clutch has definitely evolved after the first 500 miles of "break-in", then further after another 1,000. The transmission's shift action at the outset was very smooth. but the engine felt very tight, even at the low RPMs I maintained at the beginning. Then after about 500 miles the engine started loosening up and it felt easier to push engine to what feels like more natural shift points. Then after 1500 miles the whole system started to synch nicely. Now very fun.

I happen to have 4.10s in my Rubicon and think that Jeep is failing manual buyers by putting anything <4.10s in any manual diffs. If I had any other trim level I probably wouldn't love my manual as much as I do.

 

[R00STER]

It's absolutely not a good idea. It will obliterate the synchros in short order if you aren't exactly in sync. With that said, I always try to get a grasp on this in any vehicle, so I'm shifting without harming the synchros.

Cheers mate. Sorry I didn't mean to inadvertently spotlight you; your post was clear on why you were doing it and it made sense within the context.

I have read most of the manual tranny threads on here and clutchless shifting has been mentioned a couple times. Since this was the most recent thread to so, so i'd thought i throw it out there to any manual noobs.

I highly recommend anyone driving a manual to watch a youtube video on how a manual works, it may change the way you drive it. My wife used to hold clutch down at all red lights, trains, and drive through lines until i showed her the video and how it causes premature failure of the throw out bearing. It took someone else explaining it to her for her to finally listen.

 

[omnitonic]

I happen to have 4.10s in my Rubicon and think that Jeep is failing manual buyers by putting anything <4.10s in any manual diffs. If I had any other trim level I probably wouldn't love my manual as much as I do.

I definitely agree. The 3.45 gears are just too tall. I started driving it like a 4-speed, and got better gas mileage not even touching either of the overdrive gears. Now I'm on 35s (and there are plenty of other JLs out there on 35s!) and the need to regear is even stronger than before. I can get around, but I am not being kind to my clutch. I'm basically pulling out in 2nd gear all the time.

Need to make some phone calls and get that ball rolling today, actually.

 

[omnitonic]

Cheers mate. Sorry I didn't mean to inadvertently spotlight you; your post was clear on why you were doing it and it made sense within the context.

No worries. I'm agreeing with you vehemently about the risks. It's much safer to float gears in a box with no synchros. I do practice how to shift any box with no clutch, just in case, but I don't want anyone to get the impression I do this in routine daily driving.

My wife used to hold clutch down at all red lights, trains, and drive through lines until i showed her the video and how it causes premature failure of the throw out bearing.

That's actually an interesting point too. I've spent something like 92% of my manual gearbox time driving big trucks, and most of them were used trucks that had been driven by someone who didn't understand the clutch brake. Most of them didn't have much or any clutch brake left. Kicking out of gear to sit at a light for a few seconds is not really a good option in that case. Time to move. GRRRRRRRRRRRRRRRRRrrrrrrrrrrrrrCLUNK chucka chucka chucka THUMP! Oh. I moved two feet. Time to brute force this thing into gear again. Oh. Two more feet. So yeah, no, I would just stay in gear and hold the clutch pedal indefinitely, unless I was stopping long enough to pop the brakes.

Everything in human size world is a lot less heavy duty, and I probably am doing bad things to my throwout bearings on my Jeep and my old truck. There is really no need to do this, because with synchros you can just go straight in gear quickly. Hmmm. Also, even though 1st gear in my old truck does not have a synchro, it's still not nearly the same experience. Maybe the countershaft in the big honking huge truck transmission just has a lot more momentum. You pretty much can't sit there and just wait for the gears to slow down. If you miss the window to stick it in, you have to let the pedal out and spin them back up, and do the whole thing all over again. Grizzly, destructive business.

Trucks I got early enough in the game never had the clutch brake problem. There just weren't too many of those over the years. Old, ugly trucks get you home a lot more than pretty, new trucks. I was always willing to deal with those issues in order to spend less time working.

 

[CoolTech]

My late year JLUR never had the rev hang issue, but it could be possible that Jeep purposely included a rev hang on earlier models because they know most manual drivers won't rev match prior to shifting either up or down (even the ones who have driven manuals for 50+ years). Just a theory.

Good theory, but no. The rev-hang is purely there to satisfy emissions. Too quick of a rev-down typically results in too rich of mixture and so the ECU controls a slower-than-you-would-expect descent of RPMS to mitigate a brief over-rich condition.

I wonder if a pedal controller like a Pedal Monster or Pedal Commander could help with the rpms hanging?

Won't help. ECU is oblivious to a pedal commander - it just sees a different "curve" on the throttle linearity curve.... but it will still control an RPM descent.

I wish it wasn't so!

 

[Maverick909]

rpms holding is common on all new manual transmissions. the 350 and 370Z acutally does full rev match when shifting without the clutch being needed. rather weird to drive until you get used to it. ive had my jeep 3 years and ive never seen it jump to red line when shifting. It does however hold the last rpm for a second or so while shifting to the next gear to help it be smooth. all new manuals are like this. once you get used to it its not to bad. It also makes rev matching alot easier than the old days. One thing that can happen is if you dont pull your foot up all the way off the gas pedal the 3.6 will rev very quickly. Peppy little motor it is. i would have the dealer check it out though. seems fishy that it wants to redline when shifting.

 

[mickyjl13]

rpms holding is common on all new manual transmissions. the 350 and 370Z acutally does full rev match when shifting without the clutch being needed. rather weird to drive until you get used to it. ive had my jeep 3 years and ive never seen it jump to red line when shifting. It does however hold the last rpm for a second or so while shifting to the next gear to help it be smooth. all new manuals are like this. once you get used to it its not to bad. It also makes rev matching alot easier than the old days. One thing that can happen is if you dont pull your foot up all the way off the gas pedal the 3.6 will rev very quickly. Peppy little motor it is. i would have the dealer check it out though. seems fishy that it wants to redline when shifting.

Thank you for writing back. It makes sense what you write. Very annoying though.

At times I want my Jeep to be fitted with Webber carburetors and forget all the electronic stuff. I don't know if that is legal in the US and if such carbs and manifolds are offered. I guess the only option is to buy an old one.

Take care!

 

[Maverick909]

Thank you for writing back. It makes sense what you write. Very annoying though.

At times I want my Jeep to be fitted with Webber carburetors and forget all the electronic stuff. I don't know if that is legal in the US and if such carbs and manifolds are offered. I guess the only option is to buy an old one.

Take care!

Its. I thing like the old days where you had to know how to drive. Most days I wish all cars where three on the tree again

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