Ok so hears the deal. whenever disconnect my battery and allow the ecu to reprogram i get EXCELLENT gas millage (like 45 in a ej2 with auto trans!) then the longer i let it go the gas millage get worse (it goes down to like 34-36 and stays around there) and the longer i let it go the harder the trans shifts. so what i did is i installed a switch under my drivers seat (with my other switches) that turns off the ecu. i got a fuse tap and ran 2 wires to under the seat (with an inline fuse) another cool feature about this is that i dont have to reset my clock or radio, and the car wont start with the ecu off so it acts as an anti-theft device as well. my only question is if there are any bad side effects to turning the ecu off frequently. i drive 35 miles to school and im wondering if its ok to turn it off both at school for 8 hours and then for 12hours when im at home. there has been a whole bunch of carjackings in there area and the police think that the suspects have master keys so it would be nice to have the extra assurance but if this way is unsafe in anyway i can very easily run another pair of wires for like the starter or something

 

How do you calculate gas mileage? How did you discover this effect? Is the CEL ON? Do you get the same effect by removing the 7.5A Backup fuse under the hood?

 

i calculate my gas milage by dividing the miles driven by the gallons taken to fill up the tank (i always fill it up all the way at the same station and same pump). I discovered this when i was upgrading my stereo and every tank after the battery was unplugged got rly good gas millage. i confermed this by pulling the 15 amp "ecu" fuse under the hood, keeping it outfor 15min and the putting it back in and driving as normal. i have not tried the 7.5amp backup fuse. btw my CEL light has NEVER been on (the bulb works).

 

Pulling the ECU fuse with the key off should have no effect whatsoever. That circuit is active only with the key on.

When the key is off, the ECU receives power only from the backup fuse to keep the memory alive. The car will still start and run with the backup circuit dead, but codes will not be remembered.

 

the car WILL NOT START with the ecu switch off

 

i have a master shut off too...

 

True, it will not start with the ECU fuse out. I'm saying that cutting the ECU fuse should not reset the unit's memory though, that's what the backup fuse does.

 

It's really difficult to understand or believe the effect on gas mileage that you are claiming. The 15A ECU fuse (#31) under the hood controls voltage to the main relay, ECU, and fuel pump but is not responsible for storing any ECU memory. This circuit only becomes active after the ignition switch is turned ON. Fuse 32 (7.5A) controls ECU memory.

 

dito sounds odd. ya sure you had the stereo going when driving afterwards?
i know my stereo cuts my milage down about 2-3mpg its the weight plus the draw on the alternator killing my milage alittle small price to pay for some BUMP. LOL

 

heres the deal i was in a hurry when i posted last (at school) i get what ur saying now. i dont know if the ecu switch will have the same effect as disconnecting the battery. i just put it in the other day and im experimenting if it has the same effect as disconnecting the battery... i always drive with the radio on at the same volume... i also noticed it AFTER the stereo had been in for months... (i was using the spare tire well for my amps but i got sick of the spare rollin around in the back seat) i dont know if this has any direct effect on mpg but the trans shifts like its BRAND NEW... i invite all auto owners to unplug there battery and feel the difference