What would cause my car to run extremely rich all the time? The only cels ive thrown are VSS (doesnt malfunction anymore) and Code 1 (obd1) Oxygen Sensor Content. The car has no power down low which i believe is due to a large exhaust leak that i have because above like 3000 it pulls awesome. Im not sure why I am throwing an O2 sensor code but i have swapped O2 sensors, checked the wiring, tested the circuit and everything seems to check out.

 

Without a properly working o2 sensor the ECU has no idea what the A/F ratio is, thats probably why you are running rich. IS the ECU chipped?

 

ecu is 100% oem, no chipping or modifications as far as i know. I dont understand why the O2 sensor would be malfunctioning though as ive swapped between 2 known good O2 sensors and it didnt make a difference. What other causes could there be? improper wiring (i hardwired the car to obd1)

 

If I were you I would check the resistance & continuity between the 02 wires straight into the ECU pin, if that checks out make sure all the pin are completely push in in their designated holes. Also make the contacts are clean and straight.

 

ok I have 2 different sets of info here on the O2 sensor. One is saying that when the engine is cold it shoud read between 0.1-0.2 and when it begins to warm up it should fluctuate between 0.1-0.9. The other info is saying I should see 0.4-0.5 with key turned to the on position and it should be less than 0.1V after 2 minutes which is exactly what im experiencing.

the P02SHTC reads battery voltage with key in ignition which is correct.

I dont understand what the hell is wrong and making me throw an O2 sensor code. Is there anything that would cause the engine to run rich enough to throw an O2 code?

 

What car is this? What engine? What ECU?

Which O2 code are you throwing? The one for the actual O2 sensor or the heater portion of the O2? When you say the PO2SHTC measures battery voltage, that sounds like the heater section you're talking about. But when you talk about .1-.9v, that is the actual O2 sensor.

If you were running rich enough, you should have tossed a fuel supply code.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by scarlemthug &raquo;</TD></TR><TR><TD CLASS="quote">improper wiring (i hardwired the car to obd1)</TD></TR></TABLE>

It sounds like your wiring job is a little suspect.

 

1998 Honda Civic DX (Originally Auto), 1997 B18b1, P75 (OBD1 ECU).

I am throwing a code 1, I believe that is for the heater voltage sensor. When I test the voltage sensor portion it starts between 0.1-0.2 and then slowly drops to 0.04x when the engine warms up.

With the key in the ignition the Heater circuit reads 12.xx.

The only codes ive thrown are VSS (speedo would jump around and stop working randomly before). and Code 1 for the O2 sensor.

The wiring I have double and triple checked to make sure every wire is connected if its suppose to be connected and that all the wires are connected to the right wires. I hard wired it because i didnt feel like spending $100-150 on a conversion harness when i could get the OBD1 plugs for free.

There is continuity between all of the O2 wires and the connections at the ECU.

 

Code 1 is for just the O2 sensor - not the heater. If the heater had burned out, you wouldn't even have to start the car to get the CEL on (Code 41), just turn the key 'on'.

When you say hardwired, what did you do, get some OBD1 P75 ECU connectors and solder directly to your stock harness (after cutting off the OBD2 ECU connectors)?

When I monitor the O2 voltage with a scantool, on a cold engine, the O2 is usually spitting out .9v. Either way, once the engine gets hot, is your O2 oscillating between .2-.8v or so? If its not, remove the O2 from the exhaust, throw it in a bench vise and use a propane torch to heat it up while using a meter to monitor its output voltage. As you wave the torch over the thimble, the voltage should change. An O2 sensor doesn't monitor a/f ratio - it really monitors an air to air ratio.

If the voltage is now changing like it should, you can suspect your wiring.

 

oh, so its not the heater then . Basically i found an OBD1 prelude in a scrap yard and i cut off the ECU plugs and i used about 3-4 references for knowing which wire connects to which wire and i soldered all connections properly, after cutting the obd2 plugs off.

In my manual it says when the engine is cold the O2 is in open loop i believe and should be giving me a reading between 0.1-0.2V and when the sensor goes into closed loop (engine warm) it should be reading 0.1-0.9V. Now this is OBD2 info whereas the OBD1 stuff is saying that when cold i should see 0.1-0.2 and then it should drop to under 0.1V when warm? I have 3 O2 sensors, 1 from the original swap and 2 from the D16y7 that was in the car before. I have swapped from the original one (which i know was working before the swap) with one from the D16 and it made no difference.

So if i take the old original O2 and i do the bench test and i dont see what u described then what in my wiring would cause the problems when all of the wiring is correct wire on ecu plug is soldered to the correct wire going to the O2.

 

.1-.9v...good enough. Point is, it needs to oscillate when its hot - is it?

If you do the bench test and the O2 shows a voltage swing, then plug it back into the harness and get a friend to perform the test with the torch again. Meanwhile, you disconnect the ECU connectors from the ECU and make sure the same voltage you just measured in the vise is now appearing at the proper ECU spots.

 

yeah when its warm its not oscillating its steady below 0.1V. The thing that confuses me is why for the OBD1 stuff does it say when its warm it should read below 0.1V at all times?

 

That doesn't make any sense at all. The O2 has to oscillate - that's its characteristic operating nature. If it sat at .1v all day long, I would hope the ECU would throw a code.

So, try the bench test to make sure the wiring job isn't somehow loading the O2 down and keeping it from working, especially since you said you took one out of a working D16Y7 setup.

 

I dunno, it just said that on one of my obd1 wiring schematics it said that the sensor should read .4-.5 with the key in the on position and under .1 with the engine warm.

I just tried to test one of my other O2's connecting my multimeter to the white and green wires and i passed a flame over the tip and it didnt change at all.

What could be wrong with the wiring if there is continuity from the ecu connector all the way to the o2 sensor connector and there is under very little resistance (0.6ohm or something like that) in the wiring?

The car runs fine and every it just runs really rich. The only time it throws an o2 code is usually when im going onto the highway sometimes it will throw a code but if i turn the car off and restart it the code goes away and doesnt come back.

 

An O2 sensor needs to get to 600*F before it ever thinks about spitting out a voltage. If the O2 is good, and the wiring is checking out fine, then try another ECU.

It can't be but one of three things: the sensor, the wiring, or the ECU.

 

ECU was fine before it was put into the car, O2 sensors were all good before swap and the wiring has been checked and it all seems to check out. I have no idea why i would be getting the weird readings im getting if your saying it has to oscillate when its in closed loop?

 

maybe this pic can help

 

yes the white wire is the one im testing for the signal, I have 12V at the black wire aswell (except when the car is running i think it dropped down) And I have continuity from the green wire to the ecu.

 

As I said, it can only be so many things. If you know the ECU is good and you know the O2 is good - its gotta be your wiring. Which spots on the ECU plugs are you using for the signal and ground? You may have continuity from each wire back to the ECU, but maybe you have the O2 input at the wrong spot.

 

white wire from the O2 sensor goes to pinout D14 on the OBD1 ECU, O2 sensor ground (green) goes to pinout D22, Heating element (black) goes to pinout A6.

nething wrong here?

 

top

 

That is correct.

So with everything hooked up, car warmed up and you're cruising down the road: Is the O2 sensor swinging?

If its not swinging, then you need to find out why. But as I've mentioned, you can do the bench test to verify its operation. And if you can't get it to work in a bench vise, don't assume it'll work when put into your car.

 

hmmmm, ill go test it with the car cruising down the road and see if it works properly then.

 

anymore insight into my problem?

 

Is the O2 swinging? Or sitting still @ .1-.2v while warmed up?

 

ill go test right now, 5 minutes