No 5th gear

IronCity

IronCity

TJ Enthusiast
Joined
Dec 8, 2016
Messages
438
Location
NJ Toms River, NJ, United States
When traveling on the parkway/freeway and hit 5th I lose speed and RPM's and have put it into 4th and keep it there. When I'm on regular state roads and put into 5th it climb slow and sound like it's bogging.


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Sounds like crappy gearing to me as well.

If that's not the case, have you scanned it to see if there's any codes being thrown?
 
IronCity said:
No def not, I have a 4.0 with 31's that I've been running since I got it. This problem is new.
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Any Check Engine light? The two possibilities that immediately come to mind are a bad upstream O2 sensor causing an incorrect air-fuel mixture or a partially clogged catalytic converter plugging the exhaust.
 
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Jerry Bransford said:
Neither will necessarily cause a Check Engine light.
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Will the upstream O2 Sensor cause a slight rough start when the engine is cold? I've also noticed that recently when starting her up in the morning. Not talking a 10 sec turnover but used to turn the key and it started right away. Now it like 1 second


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IronCity said:
Will the upstream O2 Sensor cause a slight rough start when the engine is cold? I've also noticed that recently when starting her up in the morning. Not talking a 10 sec turnover but used to turn the key and it started right away. Now it like 1 second
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Not when the engine is cold. The computer doesn't look at the O2 sensors until the engine has started to warm up.

And to confirm, after the Jeep has sat all night or all day, it still starts up ok within a second?
 
Check Engine light etc is never instant. Ive had a bad O2 sensor, rebooted the system and driven for weeks before the Check Engine light reignited. Honestly only time will tell with engine diagnostics,
 
Jerry Bransford said:
Not when the engine is cold. The computer doesn't look at the O2 sensors until the engine has started to warm up.

And to confirm, after the Jeep has sat all night or all day, it still starts up ok within a second?
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Yes, if I park it at night n start it in the morning it hesitates for a sec then starts. The rest of the day it's instant. If it's any of the above how would I tell, time or is there at to diagnose.


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With a 4.0L engine in 5th and you are running 3k rpm at 60 mph, your gearing is not bogging you down, gotta be the engine. Air filter good, fuel filter, plugs... coolant temp good? Pretty much the first item that impact power/performance. After that, exhaust don't smoke.. compression check per cylinder?


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IronCity said:
Stock gears that come with the 4.0X. At 60 in 5th I'm prob around 3 RPM's I know when I'm on the freeway at 75 I'm at 3.5 RPM's


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This is unrelated to your problem, but stock gears on a 4.0 producing 3.5k RPM at 75? That's incredibly high for a stock Jeep turning 31's...even a Rubicon doesn't turn RPM that high. Unless you have a 6-speed.
 
I did some more looking and asking and everyone I've talked to said my RPM's at 75 are within acceptable range. I'll def start with changing my filters and move on from there. That's for the replies.


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For reference - My Rubicon (4.0 & 5 speed) on 265/75R16's (31.5") with stock gearing (4.10) runs about 2800-3000 RPM's at 75 mph.
 
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