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Old 17-06-2017
markwiseguy  markwiseguy is offline
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Default CRD Trans/Overdrive weird RPM on HWY
Anyone experience this-

Driving at 100 or 110, engine RPM will sit around 1900ish...
Accelerate so revs increase over 2200ish and then back off to cruising speed and it then sits around 1700 RPM! and will stay there until i slow down.

So if i sit with cruise control on for hours (long trips) i make sure its RPM is 1700 rather than 1900.

Is this a fault with overdrive?

GDE tune (eco)
Scangauge
2010 Auto JKU - 2,700kg
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Old 17-06-2017
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Classic Boy  Classic Boy is offline
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I reckon the second rpm maybe due to the torque converter locking up, they typically drop around 200 rpm. Why it doesn't lockup until it has been accelerated above 2200rpm and then backed off is odd.

They normally get commanded to lock up or unlock by the TCM based on a calculation of inputs from road speed, engine load, throttle position, trans temp, engine temp, transmission selector position and the actual gear the trans is in.

If my suspicion is correct I have seen map sensor problems cause trans slow shifting, because the engine load data is provided by the ECU to the TCM to determine gear selection.
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Old 17-06-2017
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Are you running larger diameter wheel/tires ?


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Old 18-06-2017
markwiseguy  markwiseguy is offline
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Yes, 33" muddies. I have a AEV Procal to adjust...

Could be tire increase problem u think?
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Old 18-06-2017
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I agree, the RPM drop sounds like the TC locking up....but I'm not sure why you have to increase RPM before it'll do it.....it should lock up at light throttle/constant speed setting....above a certain set speed. If you're able to, you might check to see if its throwing any codes.
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Old 18-06-2017
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Quote:
Originally Posted by markwiseguy View Post
Yes, 33" muddies. I have a AEV Procal to adjust...

Could be tire increase problem u think?
ofcourse it is.. Remeasure the tyres to its true size and reprogram it.
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Old 19-06-2017
samft  samft is offline
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It's the TC lockup for sure

You're doing the right thing by making sure it clicks into 1700 rpm for long drives.

Basically it's churning fluid at 1900rpm which will use more fuel and create transmission heat.

Unfortunately the behaviour sounds normal if you have 33's and haven't re-geared

I have 35's and 4.88 gearing and I get a similar thing occur but around 95km/h from memory

Have you got your scangauge set to show transmission temps?
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