87 upshift light??s

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Mar 23, 2010 | 06:23 PM

hennigm4

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Joined: Jan 2010

Posts: 120

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From: leesburg

Year: 1987

Model: Cherokee

Engine: 4.0

87 upshift light??s

So my 87 5 spd has an arrow that points up, its yellow, and i think is supposed to help with fuel economy by telling you to shift up. Mine comes on while driving in 5th gear at highway speeds, kinda like it wants me to shift down, but this is 65 mph, too fast to shift down....What controls this light? Vacuum, oxygen sensors??? Any idea??

Thanks,

mike

Mar 23, 2010 | 06:33 PM

96Cherokee113

CF Veteran

Joined: Nov 2009

Posts: 1,261

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From: New Jersey

Year: 1996

Model: Cherokee

Engine: 4.0 HO

Quote:

Originally Posted by hennigm4

I'm pretty sure it goes by how many RPMs your at. Mine doesn't even work and I never listen to it anyway when it decides to work randomly. It always wants me to shift at like 1800-2000 RPMs. Yours is a Renix, so the technology isn't fantastic, so it probably doesn't realize you can't upshift any higher than 5th gear when you reach the certain RPM that the light comes on at. You can always put it in Race (the R on the bottom right) after 5th, but would be consuming lots of gas and transmission internals

Mar 23, 2010 | 07:06 PM

schmaunty

Member

Joined: Jun 2009

Posts: 177

Likes: 3

From: Canada, Manitoba

Year: 1988

Model: Cherokee

Engine: I6 242cid

my light works and i think it goes by the RPM. It tells me to shift in 5th too. Gotta love Racing gear

Mar 24, 2010 | 09:51 AM

TheNerd

Seasoned Member

Joined: Oct 2009

Posts: 254

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Year: 2001

Model: Cherokee

Engine: 4.0L

From part of the FSM from '88:

Quote:

The shift light system is used on all manual transmission equipped vehicles. The ECU monitors coolant temperature, throttle position, vehicle speed, and engine speed to control the shift light. The ECU calculates what gear position the vehicle should be in and uses this information to turn on the light. The light indicates the best shift point to the driver for maximum fuel economy.
... A transmission-mounted switch prevents the light from illuminating when the transmission is shifted into high gear. The ECU turns the light off if the shift to the next higher gear is not performed within 3-5 seconds after light comes on.

Perhaps they are mistaken about this so-called transmission-mounted switch. I know my Peugeot tranny had so such switch, nor does the NV3550 I put in its place. It could have been carry-over info from Pre-87 models.

Either way, it appears there is a little more to it than just the engine RPM.

Mar 24, 2010 | 06:55 PM

littleredXJ

Member

Joined: Nov 2009

Posts: 180

Likes: 1

From: Olympia, WA

Year: 90

Model: Cherokee

Engine: 4.0

I have a 90 and the shift light comes on every now and then when i'm in 5th gear. It's just one of those things (it is 20 years old after all). The last post is pretty much spot on about how the renix computer decides to turn the shift light on.

Mar 24, 2010 | 08:23 PM

hennigm4

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Member

Joined: Jan 2010

Posts: 120

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From: leesburg

Year: 1987

Model: Cherokee

Engine: 4.0

Hmmm, that makes sense, where exactly is the ECU located, it may have an issue which would explain some other problems with the jeep.

Mar 25, 2010 | 01:26 AM

littleredXJ

Member

Joined: Nov 2009

Posts: 180

Likes: 1

From: Olympia, WA

Year: 90

Model: Cherokee

Engine: 4.0

ECU is to the right of the steering column behind the trim, pretty much in front of your right knee when you're driving.

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Jan 26, 2011 | 10:06 PM

Jimmer818

Newbie

Joined: Jan 2011

Posts: 9

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Model: Cherokee

I know its and old post, does anyone know if the shift light is adjustable, my cherokees a 91.

Jan 27, 2011 | 08:01 AM

hennigm4

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Member

Joined: Jan 2010

Posts: 120

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From: leesburg

Year: 1987

Model: Cherokee

Engine: 4.0

not sure, i replaced injectors, iac, map and tps, she seems normal now, still have a vacuum leak at manifold, just waiting to check compression before i waste time replacing that gasket. Also changed 02 sensor.
Mike

Jan 27, 2011 | 08:06 AM

#10

96xj4x4

CF Veteran

Joined: Nov 2009

Posts: 1,291

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From: Manahawkin New Jersey

Year: 96'

Model: Cherokee

Engine: 4.0 160k banks header dumping after the cat

Quote:

Originally Posted by Jimmer818

I know its and old post, does anyone know if the shift light is adjustable, my cherokees a 91.

i highly doubt its adjustable, if you really need to know when to shift take a red sharpie and draw a little line on your tachometer where you want to shift