Gummie

My check engine light came on the other day after I had been fooling around with my headlight module. Those things are a pain in the rear to get in/out with that huge clump of wires in front of them

All went happy and well (the headlights work - all it took was new motors and a junkyard module) until I started the car. It immediately threw a code. I flashed out a 13 - oxygen sensor open. I looked around under the hood and saw that I had somehow managed to unplug a harness that's on the far right side of the firewall (one of my friends said it was a signal amplifier?). I plugged it back in and started the car and the code was gone.

All was good again until I drove about 10 minutes down the road and the check engine light came on again with another code 13. I pulled over and poked around under the hood but didn't find anything else obvious. When I started the car again the code was gone. I drove aprox 10 more minutes and the light came back on. Stopping the car, waiting about 10 seconds, and starting it again made the light go back off... for another 10 minutes of driving.

Nothing note worthy happened each time the light came on. No big bumps in the road, no hard acceleration/braking/turning, just cruising.

Two things come to mind

One of the wires in a harness might not be all the way connected (I might have partially unplugged another harness but can't see it). Anyone have a diagram of the O2 circuit for an 88 TPI so I can trace it?

The second thing has been happening more and more for the past month or so. Whenever I start the car I get a nice white cloud (no, not blue – it’s too much gas). I also could also smell gas from time to time from the exhaust, even after I stopped the car (stop car, get out, walk around it to go somewhere, smell gas). I was blaming it on the cold start/other 8 injectors (bad injector tick, etc), but could it have been the computer compensating for a dying O2 sensor? I've never had an O2 sensor fail before, so I don't know what they do. Is it possible for them to gradually read leaner and leaner so the computer sends more and more fuel?

Danno

First, the O2 sensor does nothing on cold start. It won't begin to signal until it reaches approx 500-600 deg. Yes, they get what they call "lazy" as they get old. I would go over the connector you unplugged and hit it with some contact cleaner and make sure it is mated well. You can pull out the sensor and inspect it. It should look whiteish, if it looks black then it is most likely bad. Single wire sensors have an average life of about 25k miles before they start to go, and a lot depends on the driving you do.

bscivolette

Im no expert, but in my experience if you are smelling fuel then your fuel is running rich...and if thats the case then your O2 sensor is either dead or dying. There cheap for old Camaro's , mine as well get a new one.

Gummie

Damn, you're right. The sensor will only cost me $20 as compared to the $65 my mom just spent on one for her civic. I will post results after I purchase/install it tomorrow or Sunday.

Danno: good call on the oxygen sensor not being functional until the engine changes loops. I have Accel 23# injectors (trying to stay close to the stock 22# rate – once I build the engine up I will swap to better/bigger injectors) and a cold start plug kit in the mail. If all goes according to plan I should be able to get that done on Friday.

Hopefully a combination of these two things will cure running rich and the white cloud. If not I will move on to new heads since I don't see the point in putting the money/effort into replacing the valve guides/seats.

I would still like to trace out the circuit to see if anything else got pulled aside from that one connector. It will be much easier if I know where wires go instead of trying to trace them in the crammed corridors of the engine bay.

Thanks for the replies so far

Danno

You might want to try a Bosch universal heated sensor, they react faster and are more efficient than single wire non heated units.

Gummie

Exactly what I got

Anyone have a diagram for the o2 circut (ie where the wire is run to/from)? Please?

net_coma

iTrader: (3)

According to the 1985 Shop Manual the O2 sensor (one wire) goes to the D7 terminal on the ECM

"The ECM supplies a voltage of about .45 volt between terminals D7 and D6 (D6 is ground potential). If measured with a 10 megohme digital voltmeter, this may read as low is .32 voltss). The O sensor varies the voltage within a range oa about 1 volt if the exhaust is rich dwn through about .10 volt if the exhaust if lean.

The sensor is like an open circuit and produces no voltage when it is below aobut 360C/600F. An open sensor circuit or cold sensor causes an open loop operation."

Book happened to be open to the page...mine started throwing a code 12 and smells rich. So I am chasing a similar problem on my 88.

If you need more info send a PM and I will transcribe additional info that may help.

TexasSilhouette

iTrader: (4)

Code 12 is normal unless your engine is running.

O2 Sensor generates voltage < 1.0V at very low amperage relative to exhaust O2 content.

Gummie

Thanks to all for the info. I have the new oxygen sensor sitting in my center console but I have not had a chance to install it yet. I finally noticed that the light comes on when I reach operating temperature. I guess that makes sense since the o2 sensor shouldn’t be in use until the ecm changes loops.

Hopefully I will have a chance to do this over the weekend. I will keep you guys posted.

Gummie

Turned out to be the o2 sensor was dead. The new injectors also helped cut back the smell of gas.

I'm just updating because far too often in my searches I would come across a thread that would just end after a promised update.

Thanks all for the help