[EcoCivic]

I have been experimenting with manually controlling the torque converter clutch lockup on my 2005 Honda Civic to improve fuel efficiency and performance. o far so good. HOWEVER, I am not completely sure what effects these mods can have on the short term or long term reliability and longevity of the transmission. I do not think that I am doing harm, but I am far from a transmission expert and I may be causing damage, so please proceed with caution if you choose to do something similar. Also, keep in mind that my PCM is not stock. It is from a JDM Honda Stream, so I am not sure how a USDM PCM would react to these mods.

The first thing I did is I unplugged the connector from the TCC control solenoid, plugged in an extra solenoid with the same connector so it didn’t set a code and go into limp mode, and just wire a switch to activate the solenoid. The switch did work. However, it didn’t provide complete control over the TCC lockup. For example, it would not lock in first gear, it would not kill the engine if engaged while idling in gear, and it would not engage the TCC clutch if the trans was manually locked in second gear. Also, if I pressed the gas more than a little bit with the converter locked, the PCM would somehow unlock the converter partiallly, which really confused me at first.

What I ended up doing is bypassing the clutch pressure control solenoids by unplugging them and plugging in extra solenoids to keep the oil pressure high constantly and wow what a difference that made! The trans now shifts MUCH quicker and firmer, which I prefer. IMO it is not harsh at all as long as it isn’t shifting with the TCC locked.

But more importantly, I now have full control over the TCC lockup. I can force a lockup at will, regardless of speed or what the PCM wants. IMO that is pretty cool for a couple of reasons. One is obviously the potential for better gas mileage, and another is something some people may not expect- In low gears at full throttle, the car actually seems to respond much quicker and accelerate better since the torque converter can’t waste power that can be going to the wheels.

However, one problem with manually controlling the TCC is that it throws off the PCM’s shifting strategy. For example, if I am climbing a hill in 3rd gear and the trans up shifts to 4th gear, the speed might be too low for the TCC to be engaged in high gear under load. I bet that if I could shift to D3 to keep the trans from upshifting to 3rd gear this would not be a problem. However, I haven’t been able to get D3 to work yet with this PCM, basically because the Honda Stream that this ECU came out of doesn’t use the TRS to activate D3, instead it uses a switch by the shifter.

So I think that I might install some type of 4 position rotary switch to manually shift the gears. I have already determined which solenoids are activated in which gear by running the car in gear with the wheels off the ground and checking which solenoids get power in each gear. Basically, one solenoid is activated for first gear, both solenoids for second gear, the other solenoid is activated for third gear, an both solenoids are off for 4th gear.

Anyways, any thoughts, suggestions, questions, or comments are welcome as always