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Old 03-28-2008, 10:36 AM
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AzNMpower32 AzNMpower32 is offline
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Location: WNC
Join Date: Oct 2005
Posts: 14,125
Mein Auto: 2006 325i; 2015 Yamaha R3
Originally Posted by datawx View Post
Kicking down from 2000 RPM in light throttle driving the vehicle will start to surge, if you nail it it clears. Also it will hold in gear sometimes at 3000 RPM on flat ground for some time.

OK this will get in depth........rolling down the road at 2000 rpm at say 40 MPH and you come to a slight hill or just want to go a tiny bit faster so you ease on the gas and you get what i call a half kick down......the revs seem to do a slow kick down to take the RPM to 3000...if you keep easing on the gas very slowly so the engine is under load and you want it to pull just a little harder the engine feels like its miss firing. He egg shaped wheel feeling. I can hold this feeling right through to 4500/5000 RPM if i keep easing on the gas. Sometimes the feeling is quite violent. It will jerk me in the seat back wards and forwards! (no rude comments please) The feeling is like a miss fire of the engine or a pulsing/surging sensation.

Yesterday after picking the car up from the dealer i thought they had it fixed but this time i was passing another truck at 70-80 MPH and in that half kick down area of the tranni it started again. Now i can re-produce it at the 2000 - 3000 RPM again. The RPM needle will appear to pulse with the feeling.

I have though for a while now that this may be a tranni issue. It's almost as if the engine and tranni are having a battle as to where the shifts should take place......change no hold on a second.....CHANGE NOW......NO NOT YET.

While this jerking is happening in my kinda half kick down phase.....if you floor the gas it will clear instantly and just pull hard as it should or kick own again and be fine.

Hope this make sense and you get my message.
It sounds like the "half kickdown" is merely the torque converter unlocking. At 40-45mph in 4th gear, the rpm level should be 2250rpm-ish. In D/SD, if you encounter a hill while at this speed, the revs will jump because the torque converter, previously locked, is unlocked to give you more torque. This is normal behaviour for the 5-speed automatic. (does not apply to 6AT)

However, if accelerating at 3500rpm produces unusually rough behaviour from the motor, perhaps you are not using the best fuel available. Or there may be a problem with other internal components (fuel pump? I'm no engineer). Admittedly, 3000-4000 is what I think the roughest part of the rev band for the M54 motor. Try using manual mode and drive around town in 3rd gear (M3). Tell me if the engine is the culprit by running poorly in that rev range. If its a transmission shifting issue, manual mode should solve it because it cannot execute shifts under normal circumstances at that speed.

In my 2.5iA, slight hills at freeway speeds will also trigger a 5-4 downshift, often frequently due to the modest power of the engine. I have driven at 90mph up mountains where this occurred, and the transmission still dropped to 4th @ 4500rpm........for miles on end. I have also driven up 15% grades at 50mph where the transmission kicked down to 3rd at @5250rpm and held that for 3 miles. The important thing is: The engine is built to withstand abuse.. If you want to drive around all day at 6000rpm, the engine will not self-destruct.

Keep in mind, at higher engine speeds, shifts are usually not as smooth. When the transmission engages the Hill program and selects a downshift at 2750rpm, it is not that noticeable (this even occurs when I'm coasting sometimes). But ask it to do the same at 4250rpm, you will probably get a firm nudge.
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