Highway RPM's

GregB · **Posted:** Sun Apr 01, 2007 12:45 am

Okay. I have an auto tranny (not sure which one) model year 2002. I set my cruse or just drive at a constant 60-61 mph and my RPM's stay right at 2000. However, if I drop my speed to 57 mph, my RPM's don't go down, they got up to around 2100-2200??? I don't feel my overdrive kicking off and if I hit my o/d off button I do feel a down shift that puts me up above 2500RPM's when I'm driving at either speed.

Anyway, if I'm at 2000RPM's when going 60 mph, shouldn't the RPM's at 57 or even 55mph be less?

I did just have my tranny fluid and filter changed. I also had them hook it up to a computer to do a quick learn. I had been having a noticeable shift bump at 15 mph when I was slowing down. I was told that the quick learn would help the jeep learn my wife's and my driving habits and get rid of the shift bump. That seems to be gone, but we do occasionally have a delayed hard shift when shifting into Drive.

Any advice would be appreciated and I'll likely call my mechanic on Monday.

tjkj2002 · **Posted:** Sun Apr 01, 2007 8:48 am

GregB wrote:

Okay. I have an auto tranny (not sure which one) model year 2002. I set my cruse or just drive at a constant 60-61 mph and my RPM's stay right at 2000. However, if I drop my speed to 57 mph, my RPM's don't go down, they got up to around 2100-2200??? I don't feel my overdrive kicking off and if I hit my o/d off button I do feel a down shift that puts me up above 2500RPM's when I'm driving at either speed.

Anyway, if I'm at 2000RPM's when going 60 mph, shouldn't the RPM's at 57 or even 55mph be less?

I did just have my tranny fluid and filter changed. I also had them hook it up to a computer to do a quick learn. I had been having a noticeable shift bump at 15 mph when I was slowing down. I was told that the quick learn would help the jeep learn my wife's and my driving habits and get rid of the shift bump. That seems to be gone, but we do occasionally have a delayed hard shift when shifting into Drive.

Any advice would be appreciated and I'll likely call my mechanic on Monday.

You have the 45RFE tranny and as for the rpm's going up at 57mph compared to 60mph is the torque converter unlocked,this happens going up a hill or going into heavy wind.This is normal and mine does it also,the TCM just unlocks the coverter to get the rpm's up to get back to the cruise speed.

hyedipin · **Joined:** Thu May 11, 2006 10:20 am **Posts:** 1667

I have watched my rpm go up as I slow down on highway, not that I was slowing down but just coasting and hated it every time. It never went up to 2200, though. However, I watched my rmp stay at 2000 when I was doing 65 almost 70, it takes some practice, but give it a shot.

GregB · **Posted:** Sun Apr 01, 2007 10:32 am

Quote:

... as for the rpm's going up at 57mph compared to 60mph is the torque converter unlocked,this happens going up a hill or going into heavy wind.This is normal and mine does it also,the TCM just unlocks the coverter to get the rpm's up to get back to the cruise speed.

I think I know what you're saying, but once I get to the cruse speed of 57, shouldn't the converter lock and thus I'd see a drop in rmp's? There wasn't much wind and I wasn't going up and down hills. It still seems wierd that the tordue converter would lock and drop my rpm's if I'm crusiing at 60, but not when I'm crusing at 57?

I understand that when going up a hill, the rpm's will go up to maintain the desired speed, but I was driving for miles on a flat road, and would never see the rpm's drop.

tjkj2002 · **Posted:** Sun Apr 01, 2007 10:57 am

GregB wrote:

Quote:

... as for the rpm's going up at 57mph compared to 60mph is the torque converter unlocked,this happens going up a hill or going into heavy wind.This is normal and mine does it also,the TCM just unlocks the coverter to get the rpm's up to get back to the cruise speed.

I think I know what you're saying, but once I get to the cruse speed of 57, shouldn't the converter lock and thus I'd see a drop in rmp's? There wasn't much wind and I wasn't going up and down hills. It still seems wierd that the tordue converter would lock and drop my rpm's if I'm crusiing at 60, but not when I'm crusing at 57?

I understand that when going up a hill, the rpm's will go up to maintain the desired speed, but I was driving for miles on a flat road, and would never see the rpm's drop.

Well I know my KJ hates doing 55-60 mph,it keeps locking/unlocking the torque converter,must be that one spot where the engine is not in it's powerband with the tranny gearing.I mostly cruise at 75-85 mph and have no problems(2500 rpm).

Jeepjeepster · **Posted:** Sun Apr 01, 2007 1:31 pm

The 45rfe's must lock the torque alot later b/c my 42rle locks around 40mph and doesnt unlock till it needs it(wind, hills, etc) or I let off the gas.

DarbyWalters · **Posted:** Sun Apr 01, 2007 3:09 pm

When I had my 2002 3.7L, we tested a bunch of speeds ect and figured that the 3.7L really likes 68mph...fuel mileage and TC locked. Forgot what rpm that was?

Jeepjeepster · **Posted:** Sun Apr 01, 2007 3:59 pm

My 42rle runs 2500rpms at 80 and 1800rpms at 60mph.. The 45rfe is around 100-200rpms higher.

tjkj2002 · **Posted:** Sun Apr 01, 2007 11:41 pm

Jeepjeepster wrote:

The 45rfe's must lock the torque alot later b/c my 42rle locks around 40mph and doesnt unlock till it needs it(wind, hills, etc) or I let off the gas.

My KJ the TC will lock at 35mph if on a flat road.

desertkj · **Joined:** Mon Jan 30, 2006 8:24 pm **Posts:** 677

Jeepjeepster wrote:

My 42rle runs 2500rpms at 80 and 1800rpms at 60mph.. The 45rfe is around 100-200rpms higher.

That sounds about right. Mine hits about 2800 rpms at 80 mph (almost minimum speed on AZ highways outside of Phoenix lol).

tjkj2002 · **Posted:** Sun Apr 01, 2007 11:56 pm

desertkj wrote:

Jeepjeepster wrote:

My 42rle runs 2500rpms at 80 and 1800rpms at 60mph.. The 45rfe is around 100-200rpms higher.

That sounds about right. Mine hits about 2800 rpms at 80 mph (almost minimum speed on AZ highways outside of Phoenix lol).

45RFE(in my KJ,but I do have 4.10's and 265's)-60mph=2000rpm,75mph=2400rpm,and 85mph=2800rpm .35mph on flat ground spinning a whole 1200 rpm's.

jcphoto20 · **Joined:** Sun Nov 19, 2006 1:36 am **Posts:** 507

with a 2002, it locks the torque converter right at 60-61 in O/D. when in D, it locks at about 38-40. i love the sound mine makes cruising around about 40 at 1400 with the converter locked with my exhaust- wicked, wicked grumble.

the best cruise mileage can be had in a 2002 or those with similar tranny/gears if you increase your speed to above O/D lockup at 60 or so and then have your cruise set for about 59.5-60 that will keep it from dropping back out of O/D and will stay at 1900 at steady cruise.

at 59-60:

1900 rpm in O/D with converter locked
2050-2100 in O/D with converter unlocked
2400-2450 with O/D turned off/ in 3rd

hyedipin · **Joined:** Thu May 11, 2006 10:20 am **Posts:** 1667

Question, is it my imagination or does the jeep try to keep the tranny in the highest gear possible when the low-tank light is on - instead of downshifting? Or maybe I drive slower and with less acceleration guided by my sub-conscience?

GregB · **Posted:** Mon Apr 02, 2007 9:31 am

Thank you for all your responses. So it sounds like this is pretty normal for the tranny I have, and that I'm probably getting better economy going 60mph as opposed to 55mph.

Thanks again, now I'm gonna get LOST.

Highway RPM's

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