Shortbus64

I have a 2004 S2000 pretty much stock. a few weeks ago my car started dbogging down when I pressed the accelerator. No codes, the obdII testor shows both O2 sensor voltages drop to zero when it happens... any ideas?

engifineer

The car is leaning out severely. which is why the voltage from the O2 is dropping. So the system is not gettting enough fuel at higher throttle. So not a O2 sensor problem since you are seeing a running issue that corresponds to the O2 sensor reading.

Shortbus64

That's why I didn't just replace o2 sensors, if it had been just one, maybe... But both at the same time?WTF? They aren't Daisy chained (fed by same heater line are they?)... And it only happens after the car has been running fine for about 10 minutes.

I'm beging to think ECU, but I hope not, any ideas brilliant Honda whisperers?

flanders

No other sensors that drift off at the same time?
Does the TPS respond correctly?

engifineer

One sensor (the first one, closest to the head) is the one that fuel trim is based upon. The second one is just there to see if the cat is doing its job. So the ECU compares the output of sensor 2 with the output of sensor 1 and expects to see specific differences which tells the ECU that the cat is working. Sensor 1 would be the value that would set a stuck rich/stuck lean condition, while incorrect readings from sensor 2 only would set a P0420 code most times.

ECU is almost never the cause of an issue in a modern car. My father has owned and operated a shop longer than ECU's have been used in cars, and he has found the ECU to be the actual issue in probably less than 10 cars ever.

There really is not a reason to think the ECU or sensors are bad here. Likely, you actually have a condition where the car is leaning out under heavy throttle application. Could be injectors or anything in the fuel delivery system really. Just because it has not set a code does not mean the ECU is not working properly.