why do my RPM's never go above 3000?

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06-16-2022 | 11:37 PM

#16

cruiser54

::CF Moderator::

Joined: Aug 2011

Posts: 43,971

Likes: 1,566

From: Prescott, Az

Year: 1990

Model: Cherokee (XJ)

Engine: 4.0

Quote:

Originally Posted by IJM

Not trying to be a dick, but 3k RPM is hardly pushing it. It does perfectly fine at WOT right up to 4,800. Would I run it there all day? No, of course not.

You're not being a dick. You're telling the truth and dispelling an old myth about the 4.0. It's not a tractor motor!!

I've run these 4.0s sooo hard. I've done 3rd gear in the auto at over 4K RPM for miles.
https://en.wikipedia.org/wiki/AMC_straight-6_engine

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06-16-2022 | 11:38 PM

#17

SirCyber

Seasoned Member

Joined: Oct 2017

Posts: 471

Likes: 17

From: Western Washington

Year: 1990

Model: Cherokee

Engine: 4.0L Renix

You aren't a dick, mine will go to 4k, I get horrible shaking and it sounds like it's falling apart, but it will. never had it close to 5 though. Maybe my tach is wrong? I just personally take it a lot easier and only run to 3k rarely to occasionally. Of course I also have really bad motor mounts and virtually every bushing is shot still, so then there's that

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06-16-2022 | 11:40 PM

#18

cruiser54

::CF Moderator::

Joined: Aug 2011

Posts: 43,971

Likes: 1,566

From: Prescott, Az

Year: 1990

Model: Cherokee (XJ)

Engine: 4.0

Quote:

Originally Posted by XJ_Cherokee_99

ok so if my rpms should be shifting close to redline but instead are around 2500-3000rpm then something must be off. what can I change? does the throttle position sensor have anything to do with the rpms?

Only be shifting real high with the gas pedal mashed to the floor. Not normal driving.

Have you done this?

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06-17-2022 | 02:08 AM

#19

awg

CF Veteran

Joined: Mar 2016

Posts: 3,600

Likes: 669

Year: 96

Model: Cherokee (XJ)

Engine: 4.0

Quote:

Originally Posted by XJ_Cherokee_99

ok so if my rpms should be shifting close to redline but instead are around 2500-3000rpm then something must be off. what can I change? does the throttle position sensor have anything to do with the rpms?

What happens when you free rev it in neutral ?

If it wont rev to ~5000RPM with no load, you may have a bad TPS, or bad tacho

get an OBD2 reader for about $30

Its useless trying to diagnose these cars without one

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