Damaged O2 sensor?

G

Giro

Registered User
I finally finished my car back together after replacing the head gaskets twice, and was curious as to what is the probability that my oxygen sensors are damaged by the coolant i was sucking into the engine. When my car is cold, the AF guage seems to act normal at idle, but as it warms up, it spikes at being rich. Revving the engine a little bit causes it to go lean.

I also noticed that with the engine off, and key in the on position, when its warm, the guage reads rich, and also as it cools down, i would turn the key back off, and then on, and it would start gradally going towards lean, until it completely cooled off, and with the engine still off and key on, it would be back at lean.

I double checked all connections, have new plugs and wires, and im sure its the oxygen sensors, but just wanted some feedback if anyone has had any similar experiences. Thanks.
 
Replace them. They're relatively inexpensive and its recommended to replace when headgaskets are blown.
 
Ok, i will. I wonder if the sensors caused by first set of head gaskets to blow. Constant false rich signal would cause the ecu to compensate and lean out the engine, causing it to run very lean, which i read causes detonation, and blown head gaskets?
 
Giro said:
Ok, i will. I wonder if the sensors caused by first set of head gaskets to blow. Constant false rich signal would cause the ecu to compensate and lean out the engine, causing it to run very lean, which i read causes detonation, and blown head gaskets?
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That all depends. More common than not when O2's go they cause in intermittent CEL, though not always. Chances are high mileage/excessive heat is what killed your first set of gaskets. Though you really can't rule out the O2's, especially if they were the originals
 
My understanding is that the water from Hg failure ruins the o2 sensors. What year is your car? I've got some for a 94 that came with a kit I got off here, but they didn't work on my early model. They are brand new 60 shipped if you want them.
 
I don't think so. How many wires are there? These ones have 3. They also have a different plug than my 92 did so I'm guessing they won't fit.
 
I believe there are 4 wires, but im not 100% sure. I will check in the morning.

As to the sensors being bad, is that a reasonable culprit for blowing my first set of head gaskets that i installed? The gaskets only lasted 2500 miles, and i didnt change out the o2 sensors when i did it the first time.
 
Giro said:
I believe there are 4 wires, but im not 100% sure. I will check in the morning.

As to the sensors being bad, is that a reasonable culprit for blowing my first set of head gaskets that i installed? The gaskets only lasted 2500 miles, and i didnt change out the o2 sensors when i did it the first time.
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If it were running real lean as a result. Anything is possible. There are also a number of other variables.

How clean were the gasket surfaces the first go around?
We're the cylinder heads resurfaced the first go around?
Did you use new head bolts?
Does the engine run hot?
Do you have any mods?
What temp thermostat do you run?

You get the picture. It could be many things.
 
90sc35thann said:
If it were running real lean as a result. Anything is possible. There are also a number of other variables.

How clean were the gasket surfaces the first go around?
We're the cylinder heads resurfaced the first go around?
Did you use new head bolts?
Does the engine run hot?
Do you have any mods?
What temp thermostat do you run?

You get the picture. It could be many things.
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i did the entire job by the book, cleaned the deck surface the best i could, and finished it off with brake clean to remove any residue.
Heads were resurfaced.
Used ARP studs
Engine never overheated or ran hot.
Various mods, bigger air intake system, larger fuel delivery volume, smaller puller boosting 15-16 psi.
Cant remember specs on thermostat. Temperature sits at like 185ish.

I remember asking around on here, and i was told that the composites i used the first time should be good enough. They still blew, and ive been puzzled as to why. It would make sense if the O2 sensor caused it.
 
Giro said:
i did the entire job by the book, cleaned the deck surface the best i could, and finished it off with brake clean to remove any residue.
Heads were resurfaced.
Used ARP studs
Engine never overheated or ran hot.
Various mods, bigger air intake system, larger fuel delivery volume, smaller puller boosting 15-16 psi.
Cant remember specs on thermostat. Temperature sits at like 185ish.

I remember asking around on here, and i was told that the composites i used the first time should be good enough. They still blew, and ive been puzzled as to why. It would make sense if the O2 sensor caused it.
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Do you run a tune? The reason I ask that with mods and even something as simple as using a lower degree thermostat without the proper tune can cause issues like this.
 
Funny you should ask, just last night i found out from the previous owner that i have an sct chip tuned by Mr. Dalke.
 
looks like a nic car. Of course it could always be a freak occurence but not likely in this business. Do you have an AFR gauge in the vehicle? If so what kind of fuel air ratio's are you seeing under boost?
 
Thanks. I do have an AFR gauge, and it goes lean. I havent driven the car though, i just snapped the throttle a little bit.
 
So.....im feeling incredibly dumb right now. Thanks everyone for their input, but i found out the oxygen sensor wasnt plugged in fully, hence the constant rich signal. Plug it in all the way, and its back to normal. I still have new sensors on the way just to be safe.
 
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