Since I am unemployed at the moment, I had some spare time, so this morning I went out and pulled the ECU fuse and manually locked my door and went away for an hour. Went out and put the fuse back in and then decided it was time to run some errands. All I can say is, there is definitely a difference. The throttle is much more responsive, with very little wait to downshift when called upon by the leadfoot. A very easy, surprising mod.

 

In my 01 GS430, I noticed that shifting was delayed allowing the engine to build up more RPMs for the first 20 or so miles. After that, I think the shift points lowered again. Not really pushing the car hard, my trans seems to shift around 2000 rpms. 4th gear may even come a couple of hundred RPM sooner.



Neil

 

If Lexus's PCM has the same strategy as all the US manufacturers, this is exactly right. With OBDII it is required that the ECM compensate for differences in the manufacturing process for MAF sensors and injectors, also as these componets age and shift the PCM must compensate. To this end there are some registers that store a trim value, an offset, to set the air/fuel ratio as high as possible without detenation. For my Vette, the highest air/fuel ratio allowed with the stock programming is 12.5:1, best is ~13:1 for max power. When you pull the fuse and reset the PCM, this register is reset to 127 (range is 1-255), if your Lexus's engine is running lean when the register is reset to 127, then you'll experience a higher HP engine. With a few miles of part throttle driving the registers will be trimmed to set the air/fuel ratio to 12.5 and any extra HP is gone. If your Lexus runs rich when the register is reset, then you'll actually lose HP by resetting the PCM.

 

My car seemed to run smoother and have better throttle and transmission response, but I felt it had a little less HP then before. I am happy with the results though.

 

does resetting the ECU improve fuel economy?

 

I'll let you know on Friday. It might, but this first tank after the reset won't show it if it does because I've been having too much fun testing out the difference.

 

Last year when I was given the chance to test drive the IS350, I spoke with one of their engineers.

He told me there is no real need to unplug the ECU....all you need to do is drive around fast for a little while and it will do the same thing

I think unplugging is a lot easier than driving around and possibly geting a ticket

 

yup, that's correct, coz' the ecu is constantly learning. but reset is just faster coz' it starts out with "default"