O2 sensor 86 LX-i auto

[ecogabriel]

I am trying to get the car closer to daily driving status; I am looking at fuel economy and it is a little crappy although better than it used to be (cleaning injectors helped)
I have the O2 sensor in the crosshairs. It seems that my O2 sensor signal does not get to the ECU. When I unplug the sensor the engine light (PGMFI) does not come on (there is no code in the ECU either) Whatever other sensor I unplug, I get both dash light coming on and ECU flashing a code.

When I unplug the O2 sensor with engine running, it does not change in the way it runs at all. My experience w/other cars is that when the O2 sensor is unplugged the idle speed changes a little as the ECU gets to work with default values to compensate for the missing sensor. HOwever, there is no change.

I know the car is warm enough to be in close loop because if I unplug the temp sensor that signals that the idle speed gets a little faster (and dash light comes on). I did this when the fans came on to be sure.

I replaced the sensor a few months ago. I know the sensor is working because I checked the voltage it produces with a meter.
Also, I saw sensor signal in the O2 wire that comes to the ECU. But I am unsure if a short somewhere in the wiring is throwing the whole thing off.
I'd re-check for ground continuity in the wiring just in case; I did it and did not find any evidence of short circuit. I might try throwing a wire straight from the sensor to the ECU and see what happens... but I do not have another ECU to swap and check

Anyone has experienced something like this? Any other ideas? Thanks

:banghead: :banghead: :banghead: :banghead: :banghead:

(note: I should have posted this in the EFI section... oopss!!!)
:dunno::dunno:

[LX-incredible]

Don't know if it's the case for us, but on many cars the ECU won't look for the signal until the engine is fully warmed up and input is received from the speed sensor (car being driven).

[Oldblueaccord]

Well in your case maybe running a fresh set of wires to the ECU and see what that does for you. I dont know if you can actually test out the O2 sensor while its running. I think its a 0-1V out but but it fluctuates so much a regular digital meter prolly wont catch it.

This is all assuming an 86 EFI car works the same as the slightly newer models. I would not bet the farm that a bad O2 would make code.

Whats your mileage like anyway? 25 mpg would be aceptable.

wp

[ecogabriel]

ECU needs a warm-up engine to get into closed loop and use sensor input to adjust EFI settings. I'll drive the car with the sensor unplugged and see what happens. I replaced the O2 sensor in the Civic and forgot to plug it in; the check light came on immediately. There was a difference between a connected and disconnected sensor in that case; idle was slightly faster with 02 sensor unplugged.

Sensor voltage oscillates between 0-1V; a digital multimeter would show voltage change with engine load; the manual tells you what you look for.

What's odd is that troubleshooting diagrams for O2 tells you what to do when the light comes on; here, the light does not come on. Open/short O2 wire is cause for the light to turn on; either the wire is getting "signal" somehow or the ECU is defective...

Mileage? I do not drive it in freeway (it needs new tires); all is stop-and-go city traffic. It gives about about 18-19 mpg (about 17 mpg now because of the A/C being on). I gave it to my wife to drive it in her driving circuit; when comparing with her regular drive (96 Camry, 2.2L Auto) the mpg are pretty close.
But the few times I took it to the highway I did not notice any increase in MPG afterwards (when filling the tank); I should see some noticeable difference if 20/30% of highway driving is included but I did not see it.

I'll do a wiring check and eventually drive it to the junkyard and try to get an ECU from there and see what happens... at least I will know firsthand if the ECU I'm getting is working.

[LX-incredible]

The 4 wire o2 sensors are different, they have a heating element that allows them to come up to temp sooner. When unplugged, you will also be getting a code for the heater circuit.

Are you having any problems at startup? I'd also look into the coolant temp (TW) sensor. Could be sending an inaccurate temp signal, preventing it from going into open loop... probably not.

[Oldblueaccord]

Eco

I might point this out you have a tendancy to answer your own questions or in this case ask a question you already have the answers to but ill bite on this one more time.

"You can read the O2 sensor's output with a scan tool or digital voltmeter, but the transitions are hard to see because the numbers jump around so much. An analog voltmeter is better for viewing transitions, but may not respond quickly enough on systems with higher transition rates. So the best instrument for observing the O2 sensor voltage output is a digital storage oscilloscope (DSO). A scope will display the sensor voltage output as a wavy line that shows both it's amplitude (minimum and maximum voltage) as well as its frequency (transition rate from rich to lean)."

End quote:



http://www.aa1car.com/library/o2sensor.htm

I got it from here its a good read.


Remember a 1986 car was one of the first to use electronic fuel injection so what works on your Civic may not be so true on a pre OBD car.

If you used a universal O2 sensor maybe the wires are switched ?

wp