93 Impreza downshift in power mode

Hi all

When I step on the accelerator, one would expect an automatic transmission to downshift and impreza has this 'power mode', which makes kinda more fun to drive.

My question is: can the sensitivity to how much the pedal is jammed down be adjusted? It takes very little at lower speeds for power mode to take over and it seems that power mode is often not really required. Sometimes the pedal is really not pressed further at all, yet 'power mode' is active. At higher speeds (>40m/h) the car behaves normally.

If it can be caused by a defective part, what direction should I look into?

Thanks for the help. Remco

Reply to
remcow
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Am I missing something here? If the trans is in "Power" mode, isn't it

*supposed* to hold gears longer and change down more readily?. What happens if you set the switch to "Normal"? Does it still do that, or show more restraint? If that changes things, then maybe you should only put it in "Power" when you want to press on or play and leave it in "Normal" the rest of the time. Cheers
Reply to
hippo

I used a pair of resistors in a voltqage-divider configuration to reduce the analog throttle position sensor (TPS) voltage signal being sent to the TCU. This reduced the "downshift-happiness" of my '02 OBS.

It works by making the TCU think that the pedal has not moved as far or as fast as it actually has.

This will however lower the full-power upshift points, and if you reduce it too far, will also lower the line pressure which can cause the lockup clutch to slip under power (NOT good). I experimented for a week to arrive at a result I was happy with. -Danny

Reply to
Danny Russell

Hey Danny That sounds like a good idea worth trying. Mine just seems ultra sensitive. Do you remember what value resister one can use? If the current isn't high, I wonder if a pot can be used.. Thanks again for that suggestion. Remco

the analog throttle

the "downshift-happiness"

fast as it actually has.

it too far, will also lower

(NOT good). I experimented

Reply to
remcow

It's been a couple years since I did it, so I had to go out and look at the values. Basically I ended up 90% going to the TCU from what it originally was. So if the original full throttle signal was 4.5VDC, now it is: 4.5 x .9 = 4.05. The resistor values I used were 114k for the series (top) leg of the divider, and 1M for the shunt (bottom) leg. I created the top leg value by paralleling a

470k & 150k.

I used a 1M linear taper pot and a digitag voltmeter during the original experimentation with values. Once I got what I wanted, I swapped-in fixed resistors for reliability.

Small changes will give you large results, so the pot will be very sensitive to small adjustments. I made sure to tap into the wires under the steering column (not sure on your model year), not at the TPS under the hood. The reason is that I wanted to affect the signal going to ONLY the TCU, not both the TCU & ECU. You'll need to consult a factory wiring diagram to locate the physical connector in the harness which feeds input to the TCU, as well as the specific pins on that connector that concern you.

Be very careful not to reduce the voltage too much, so as not to reduce line pressure at high throttle openings (firm shift) to that of low throttle openings (soft shift), or the lock up clutch will slip as a result and you will quickly burn it up (they're not very robust). Ironically, I performed this mod to help save the lockup clutch by preventing it from constantly dissengaging and reengaging. -Danny

Reply to
Danny Russell

Great Danny - thanks! I really appreciate you looking into it.

I have the schematic, so will see what needs to be done where.

Since these are huge resistances (i.e little current), I could use two resistors and a multiturn pot, scaled according to the numbers you just gave me.. The pot's swing will just be very small and will allow me with some tweaking if that is what I need.

Thanks aga>

the values. Basically I

original full throttle signal

114k for the series (top)

leg value by paralleling a

experimentation with

sensitive to small adjustments.

your model year), not at

going to ONLY the TCU, not

locate the physical

specific pins on that

line pressure at high

shift), or the lock up clutch

robust). Ironically, I

constantly dissengaging and

Reply to
remcow

I wanted to keep the values high enough to avoid causing any current loading of the TPS signal which is derived passively off of the 5k wirewound TPS pot. Conversely, putting too much more than 100k in the series leg would risk adding noise, stray capacitance, etc. I chose comfy pocket in the middle.

I considered getting really nutty and fitting a crude, RC time-contant feature that would allow me to tune the rise-time of the voltage as a result of suddenly depressing the throttle, but then I came to my senses (well almost).

I probably don't need to remind you to make sure that you bring the ground side of your divider back to the SENSOR GROUND on the same connector. It might be called something else like TCU SIGNAL GROUND or whatever.

The multiturn pot inside of range-limiting resistors is a great idea.

Reply to
Danny Russell

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