Quick question.. maybe somebody here has experienced something similar. When i first start the car and driving it around everything is normal. Im running an autometer a/f ratio guage. Well, after about 10 or 15min of highway driving, the guage goes all the way to lean and never comes back up! I cant figure out what could be causing this to happen everytime! Although, the computer is NOT throwing any codes, it is causing some jerkiness during mid-throttle.. any ideas?

 

If it was my car, I'd replace the primary O2 sensor. Sounds like the ECU is going into limp mode.

 

That was my guess too... guess ill just replace it and see what happens.. it seems funny that it would work for 10 minutes or so and then die..

 

There is no problem.

The Auto Meter gauge reads the signal from the stock narrow band oxygen sensor. It is only accurate in a very narrow range of operation and most of the time the ECU pays no attention to it.

There are two modes of operation for the ECU: open loop and closed loop. When it's in open loop, it basically uses rpm and MAP sensor voltage to pick a fuel value, and has a few compensation factors for things like air temperature. In closed loop, the ECU uses data from the oxygen sensor to adjust the fuel trim. This usually happens at wide open throttle or thereabouts, and it is the only time your gauge will be telling you anything useful.

As for limp mode, the ECU will only do that if there is a CEL.

 

I realize this... I really dont understand how the Ecu can NOT be throwing a code. i KNOW it is not normal for a a/f guage just lean out and never ever come up (the thing just stays black). I realize this is a fairly useless guage but being that it isnt working properly indicates a problem since the guage is wired directly off the o2 sensor signal wire going into the ecu.. Also the jerking of the car during medium engine load is just not right ..

 

You might have a stored code that's no longer making the CEL light up. Can't hurt to check. If you have an intermittent problem the ECU will store the code until it is reset.

 

wow... hold on... what do you mean by that exactly? As i said earlier..the car has no check engine light on. BUT, if i were to jump the green connector to flash the codes, it will flash a code 36. Of course there is no code 36 so maybe you can help me make some sense of this?? This is an OBD1 P30 ecu running a B17a... thanks so much

 

The car is in closed loop up to 72% throttle angle. 73% and higher it goes into open loop.

The gauge should reciprocate back and forth while in closed loop (99% of the time that you are driving), when you exit closed loop and enter open loop, the gauge should follow (it will no longer reciprocate back and forth)

Remember that the gauge is just a fancy 0 to 1 volt - voltage gauge, the signal from your sensor to the ECU is 0-1 volt. When the ECU faults out, the signal is 0 volts, therefore no LEDs light up on your gauge.

I can tell you that the way you describe your problem, I'm quite certain your O2 sensor is contaminated, replace it.

If you want to double check, just attach a DVOM between the signal wire at your ECU harness and ground, and the voltage should reciprocate between 0 and 1 volt with the car warmed up and idling, if it isn't replace the sensor.

 

Damn...thanks a lot sensei!! How in the hell did you know that? I am going to replace this thing immediately... the 02 sensor is actually very old..

 

My O2 is bad and I haven't had a chance to put my new one in yet.
I'm guessing my CRX has limp mode too because it the CEL comes on and it smells because I think its running richer. How much power does it probably rob?