87 upshift light??s
03-23-2010, 06:23 PM
#1
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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
Thanks,
mike
03-23-2010, 06:33 PM
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Year: 1996
Model: Cherokee
Engine: 4.0 HO
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
Thanks,
mike
03-24-2010, 09:51 AM
#4
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Year: 2001
Model: Cherokee
Engine: 4.0L
From part of the FSM from '88:
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.
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.
... 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.
Either way, it appears there is a little more to it than just the engine RPM.
03-24-2010, 06:55 PM
#5
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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.
03-24-2010, 08:23 PM
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Year: 1987
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Hmmm, that makes sense, where exactly is the ECU located, it may have an issue which would explain some other problems with the jeep.
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01-27-2011, 08:01 AM
#9
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Year: 1987
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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
Mike
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