Originally Posted by mmcrh
In my case, before TCM flash, i pressed gas pedal and the car responded with increase in speed promptly regardless of terrain. After TCM flash, when i pressed gas pedal, gear did drop, rpm did go up, and 1) on flat Rd or light/moderate uphill, e.g, on motorway either merging or overtaking, it struggled to increase speed promptly compared to pre-TCM flash; 2) on big uphill, e,g, mt ousley, i could only push speed up to somewhere between 50-60kph, fall short of wanted speed of 80kph. It begs the question why increase in rpm and drop in gear does not translate into increase in speed? Where is the missing link?
I think i mentioned this theory just after your 2nd or 3rd post on this topic, we're up to about 30 each by now
The "missing link" is the Torque converter. (There are also 3 friction clutches inside the gear box but we'll leave them for the moment)
It's a fluid coupling between the engine and the gearbox.
I wont got into the technical but .... It allows the engine to keep turning when you are stopped at the traffic lights.
You should be able to "feel" it working when you drive drive slowly in a driveway or take off from traffic lights.
Press the pedal and the engine revs go up and then the car gradually starts moving.
If you've driven a real manual transmission car it does the same thing as having the clutch halfway in allowing some "slippage" between the engine ad gearbox.
The torque converter is working all the time.
It slips a little when doing gear changes so they are smooth from one gear to another. (the 3 friction clutches also play a part)
When you are coasting on the flat, foot of the pedal, the engine revs drop but the car keeps going the same speed. That's the torque converter allowing this.
When driving at at steady load the engine is pushing the torque converter is basically "locked" (usually with a friction clutch) through the driveline so there is no slip and no energy is wasted. When driving on the highway , freeway , up mount Ousley with momentum it should be locked to get the power to the wheels, and not be slipping.
When going up a steep hill, you are saying that the gears change down to lower gear as they are supposed to and the revs come up as the engine revs faster for the lower gear.
You should be able to accelerate easier in the lower gear.
If you put your foot down in that gear the speed should increase and the revs should gradually increase too.
If your engine revs increase in that gear but the speed DOESN'T increase then this is the Torque converter/friction clutch slipping (the missing link).
If you have damaged one of the 3 friction clutches inside the gearbox maybe this might also have the similar symptoms.
If this really is the problem, It would be worse on hills because there is more loading on the engine/transmission on hills compared to the flat.
If you tried to tow a heavy trailer or did a fast acceleration 0-100 this also puts a higher load, so you might see the same thing happening
Originally Posted by mmcrh
After PCM update, i feel immediate improvement regarding increase in speed: on point 1) even though the speed increase is not as prompt as pre-TCM flash, I'm happy; 2) on point 2) above, i can only push speed up to 75kph, not happy jane. IF why the PCM update makes the car tick can be answered, then a solution to my problem would be on the horizon....
I don't know what controls the Torque converter, electronics? , computer? TCM? magic? but if it is slipping or the clutches are slipping then it's not doing its job properly.
To see where all the bits are, there's a nice cutaway picture in the this link which shows all the guts of it.
It's quite complicated as you can see but for an 8 speed design is actually quite simple and clever with only 4 gearsets and handles a lot of torque for its size.
Pretty much everything else you've described (once we get past all of the contradictions and confusion) is normal for the car.
One thing on driving as Benno / Barboots / BigSkiddy said is don't lift right off the gas when going up hill. This unloads the drivetrain completely and the car thinks you are not going up a hill.
You cant drive up a long steep hill in 8th with the engine revs down low. Not possible in any car not even a Jeep.