OK the background-
1989 L98, long tube headers using a 3 wire heated sensor, Bosch pn 13950.

Had no problems with this until I rebuilt the motor. I am now onto my second sensor since the rebuild. It was working OK until the other day. I have checked everything in the manual and it all checks out OK and points to a faulty O2 sensor. How can this be? It is only three weeks old. The other day the only thing I could find was a possible faulty connection which I repaired. The system then worked perfectly, went to closed loop and the sensor was ranging well within parameters, but now it is not. When it stops working the engine just gets a gut full of fuel because the sensor is showing lean.

Possible ideas I have but I need your thoughts.
I gutted the cat, so is the sensor not always getting hot enough even though it is a heated sensor?
Is the heat part of the sensor not working? I have wired this into the ignition wire on the fan relay. Does the sensor need 13 plus volts to get hot enough? Will a voltage drop effect the heat it produces?
Have I bought a dud sensor? If this is the case, why did the other one die after the new engine install?

Background,
Stock bottom end, Edelbrock heads, 219 cam, Superram, custom chip from ski_dwn_it.

This is all I can think might be the problem so I need suggestions. I have another new sensor, but I don't want to put it in until I know this is not going to happen again.
Please don't tell me to check MAF, injectors, wiring, etc, etc. I have done all the checks in the GM manual and everything points to the sensor.
I am so confused!!

Thanks for any suggestions
:confused:

 

I assume that when you replaced the O2's the engine ran ok and then the replacments have crapped out. Sicne your motor has just been rebuilt, I wonder if the sensors aren't becoming lazy. Can be caused by the wrong type of sealant which is now off gasing and coating the O2's.

 

Thought of that. I only used sensor safe sealant on everything. But it is possible. Is there a way of testing an O2 sensor outside the car?

 

When the motor was rebuilt were the cylinder walls thoroughly scrubbed down to remove all honing stone residue? Possibly silicates from the stones are leaching out of the cylinder walls and making their way to the O2 sensor.

To test an O2 sensor you need to heat it >300deg C and then pass the proper O2 concentration over it. Or you could install a failed O2 sensor into another Vette to see if it is working there.

However, since these sensors worked ok for a while I suspect that they realy have failed...for some reason.

 

I had the short motor built so I am not sure of this. The motor has now done 600-700 miles so would it still be doing this if this is the case?
I ran the car this morning with the scanner connected, and it looks like the sensor is working and when in closed loop it did keep dropping below 0.1 volts for a few seconds. I have increased fuel pressure and that seems to make it a bit better. I will take it for a drive shortly and see if it is any different.
Thanks for the suggestion.

 

I'm not sure how long such contaminents would leech out of the cylinder walls; I've read that it's very important to thoroughly scrub the refinished cylinder walls to remove these residues and so was wondering if it might be the cause of your failing O2 sensors.

If you are running headers is the O2 sensor farther down line than before? If you have FL headers, are they ceramic coated? What kind of air temps are you running in (I've noticed my '88 doesn't seem to like 0deg F much)?

If you tapped into a 12V relay power pin you should have enough power to drive the O2 sensor. It's my understanding that such sensors only draw a few hunderd mV once up to temp.

If you have a scan tool available it would show you if you are too lean to keep the light on with your O2 sensor.

 

I just took the car for a drive. It ran well for about 20 miles. The weather today is about 90 deg. The SES light came on and the motor started surging again. I stopped the car and plugged in the scanner. After restarting again the motor ran OK till closed loop. The light then came on again and the O2 sensor wouldn't go above .18 volts and didn't really range like it should do. The motor is surging because the O2 sensor says lean so the ECM ups the fuel making it way too rich.
It seems to be OK when the engine has sat overnight but starts doing this when the coolant temps get to about 200 deg.
Can an O2 sensor get too hot?
My headers are not ceramic coated.

I am going to put the new sensor in anyway but I still need to find out why they keep stuffing up.

 

Are you sure you tied into a 12V source that is continually hot whenever the ignition key is "on", and not just when the fan is on?

Did you choose a good ground location for the heated sensor wire?

What color wire(s) did you connect to which?

What BLMs and Intergrator values are you reading?


I'm running a heated 02, non-coated TPIS long tube headers, gutted CAT and haven't had a problem in the more than two years the sensor has been installed.

Jake





[Modified by JAKE, 11:10 PM 2/1/2004]

 

I have been running a heated O2 sensor for about 9 months with no problems. This all started with the new motor. The power wire is tied into the ignition wire of the fan realy (hot in run) the 2 wires are both white so it doesn't matter which one is which. I have checked that part of it. The sensor heats up to over 300 degrees.
Would the oil in a K&N filter effect the sensor. I was having MAF burnoff problems because of the new motor sucking oil into the MAF. I cleaned and re-oiled the filter which so far has sorted that out.

 

I put the new sensor in this morning. So far so good. I just need to get it on a dyno now to fine tune it.

 

Reading all your posts, it is appears evident that you O2's are falling because.. (1) they are either not maintaining surface temps or (2) their surfaces are being coated by something in the system. It may be a case of waiting for it to work its way out while you keep clean oil and coolant in the motor to help it along.

 

Glad you got it straightened out Tim.

I can not stress how important it is to have these O2s working correctly guys. EVERY person I do a chip for, I beg them to make sure theirs is working properly. 99% of the time, if they have any dislikes its directly related to the O2 sensor.

Most people fail to realize how important it really is. But when you think its what controls your fuel. With a bad one, you might as well give a dial **** to my 2 year old that can control the amount of fuel to your car, and tell him to turn it at will while your going down the road. Your car just is NOT going to run right.

I would like to see EVERY owner of these cars, put a digital volt meter on their o2 and periodically hook up the leads to the meter and check it for proper function.

I have written many times on how important these things are. Here is just another example. Go find the writeups and print them out. The first time your car acts funny. Pull it out and do exactly what I suggest and you will most likely find your problem.

#1 guys, it the #1 thing that will spoil your fun.

:rant:

 

Oddly enough, I'm having trouble getting my '89 to pass emissions. The O2 sensor was found to be one of the things at fault (egr valve, one bad injector.... :confused: )
Although too late, I just replaced my sensor, how do you check one for proper functioning? The new one I installed seems to make NO difference to a rough engine :cry

 

I had the same problem with the K&N air filter oil coating the MAF sensor wires. As the filter came from the factory too, not resulting from any re-oiling by me.

I discovered this when I ran Diacom and noticed my BLMs and Intergrators values were way off and the 02 voltage readings were not cycling as fast as they had been.

I shot the MAF wires with carb cleaner and removed all the oil from the K&N filter (didn't re-oil it either); seems to have solved the problem. It's been over a year now.

Jake