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2008 4.7 QD2 seems to lug under 40mph

Old 04-10-2019, 01:29 AM
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Default 2008 4.7 QD2 seems to lug under 40mph

This is my second attempt at Jeep-hood, the first being an '05 Liberty CRD turbo-diesel that died a horrible death from a broken head or gasket, ingesting non-compressible coolant into cylinders #3 & 4. Engine replacement was out of the question. But my current love, bought used w/75k mi. is an adequate replacement, having the upgraded 4.7 similar to my 2000 Dodge Dakota which continues to amaze me with it's power, performance and durability. My question with the Jeep is related to the transmision (545RFE) upshifting to 5th w/OD below 40 mph. Light acceleration doesn't cause any down shift and the engine feels like it is lugging, only downshifting with significant pedal pressure. I find myself manually downshifting to avoiding the vibration. Do I need to have the programming re-done, flashing the prom or what? The previous owner towed a small boat trailer and the vehicle has a limited function towing switch which basically moves the shift points to quite high rpm. My Liberty had so much torque from that little 4 cyl that it would just power through but the V8, although having equivalent torque doesn't seem to like low speed acceleration with the transmission set to D. Ideas?
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Old 04-11-2019, 09:16 PM
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It's possible the lockup converter isn't dropping out. Try putting just enough pressure on the brake to light the lights while under load and see what it does. It should drop out, then re-engage when you release the brake if that's the problem. Just a bit of quessing here. My experiences don't go past 04.
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Old 04-16-2019, 08:31 PM
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Originally Posted by dave1123 View Post
It's possible the lockup converter isn't dropping out. Try putting just enough pressure on the brake to light the lights while under load and see what it does. It should drop out, then re-engage when you release the brake if that's the problem. Just a bit of quessing here. My experiences don't go past 04.
Thanks for the suggestion. So far I have only been able to see any change in RPM when I tried this procedure once, but it felt like it downshifted to another gear rather than unlock. I got a nasty looking red light that came on and then went off that I think was for the electronic throttle control. Evidently it doesn't like power braking
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