This is a 4cyl Honda Accord. For over a year fuel economy has been terrible, about 16mpg with mixed driving. After reseting the computer (by disconnecting the battery) fuel economy improves significantly above 20mpg. If i run a tank or two without reseting the ecu the mileage gets bad again. No check engine codes. replaced plugs, wires, rotor and cap as well as the O2 sensor. Adjusted valves to spec. This is baffling.

The factory default values in the computer provide much better fuel economy than the adaptive (learned) values. What sensors could cause this? I doubt changing the ECU is worth it. It seems as though the ECU is learning something abberant from a sensor and adapting incorrectly to it...yet no check engine error code is triggered.

With my OBDii scanner i can read some sensors and it looks good to me. Such as the coolant temp, input air temp. Long and short term trim values hover around 0 but never positive (from about -5 to 0). Timing is about 12BTDC at idle which is spec and advances with higher RPMs. Finally no driveability differances noticed before or after resetting the ECU.

I'm reduced to resetting the ECU once a week to keep fuel economy acceptable.

Help, thanks.

 

thats good info

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by NJ VTECpowered &raquo;</TD></TR><TR><TD CLASS="quote">thats good info</TD></TR></TABLE> wtf?

alright have you check some of the key things? fuel injectors? fuel filter? maybe try a fuel injector cleaner?

 

a bad fuel filter would cause driveability problems (e.g. poor acceleration). What I need to know is which sensors are part of the ECUs adaptive (learning) system. As mentioned reseting the ECU fixes the problem tempoirarily.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by erubin &raquo;</TD></TR><TR><TD CLASS="quote">The factory default values in the computer provide much better fuel economy than the adaptive (learned) values. What sensors could cause this? I doubt changing the ECU is worth it. It seems as though the ECU is learning something abberant from a sensor and adapting incorrectly to it...yet no check engine error code is triggered.

</TD></TR></TABLE>

Yes I've heard that the ECU does adapt to the surroundings. I do this when the seasons change but once I didn't reset when fall came around and my MPG rose significantly but ran like **** when winter came But you seem to be reseting your ECu too often

 

I agree with the previous comment. It may be that you have a poor connection (electrical or vacuum) someplace or that you have one or two faulty components in the fuel or ignition departments. For example, Honda's are notorious for sensor problems.

 

Thanks for trying to help. Which sensor or system would not cause noticeable driveability problems and yet over time teaches the ECU to improperly correct something leading to fuel economy creeps away from ideal? What I need to know is which sensors are part of the ECUs adaptive (learning) system. Does anyone know?

As mentioned reseting the ECU fixes the problem temporarily. Problem is that the check engine has not been triggered which would give a hint where to look.

 

Your basic assumption about the problem may or may not be valid.

Many sensors feed into the computer. You should be given some idea by a detailed wiring diagram -- check out the sensors that are directly connected (wired) to the ECU.