Carbon fouled O2 Sensor:'92 VX - Perplexed

[Darkelf]

Originally Posted by RoadWarrior

... and clear the spectators, a cylinder full will hose anyone within 20ft with hot coolant.

Wheee! Who needs Splashin' Safari?

*sigh* Looks like I've got my work cut out for me. Guess I'll start with the EM and take it from there. Have to get a compression tester and get crackin'.

Thanks to all for their input! I'll post an update when I get more info.

[kamesama980]

coolant will clean things and not as far as I know, leave soot. http://s29.photobucket.com/albums/c2...t=DSCF1160.jpg this pic is from when my engine blew the head gasket at cyl #6. notice the cylinder all the way to the right is MUCH cleaner than the others? I didn't look down the manifold unfortunately but other than leftover oil/water mucus, the exhaust runner in the head was very clean.

[Darkelf]

OK, pulled the header and no evidence of coolant 'jetting the ports'.

I have attached pix of each port, Right to Left facing the ports. Please take a look and comment if you see anything unusual that I may be missing.

Now I'm still confused because this seems to point to a too rich mixture yet NO FOULING of the plugs.

Some things that the previous owner did that may or may not be helpful in diagnosing this weirdness:
1) said he put some seafoam in the tank. I have since run it nearly empty and refilled 3x since I bought it.
->could the carbon fouling in the exhaust ports be tail end of carbon residue being cleaned by the seafoam?
2) Put in a new O2 sensor (the one that is now fouled).
->when I bought the car I drove it for about 800miles before I replaced the plugs from ZRF5-11's to ZRF4-11's and pulled the O2 sensor just to look at it. Plugs were very clean but O2 had a bit of carbon fouling. Didn't think anything of it at the time cause this was my first VX. Cleaned off the carbon (just from the outside of the tip, carefully) and checked again when I bought a spare O2 sensor off eBay and wanted to test it. Carbon fouled again. Cleaned it off. Checked plugs again, still spotless. Drove 40miles, pulled the sensor and again, more carbon. Guess the short winded version of what I'm trying to say is that it get fouled very quickly.

Possible head gasket from 2 owners ago:
-> could a HG leak cause carbon fouling ONLY in the exhaust ports and beyond?

Right now I'm getting a CEL for the O2 sensor and getting *maybe* 28-30mpg. UGH. Don't want to put a different one in there if it's just going to get buggered again.

Where to go from here?

[92VX]

I'm confused on how long you've owned the car, has it ever run right with no CEL codes? Can you take pics of the O2 sensor, including the wiring to it?

[Darkelf]

Originally Posted by Rancho VX

I'm confused on how long you've owned the car, has it ever run right with no CEL codes? Can you take pics of the O2 sensor, including the wiring to it?

I've owned it since mid Jan 08. Never threw a CEL till the O2 sensor got sufficiently fouled a few weeks ago. It did manage to get 43 mpg on the 300 mile drive home after purchase but 'stumbled' at cruising speed, so I guess it never ran quite right. That's why I tore down the intake system (see thread:air intake system rebuild) to clean things out and eliminate variables. Ran great after that for a few in-town trips (don't drive much) till the stumbling returned much worse than before.

Hope that clears things up a bit.

One thing I have done is try and clean the sensor and bench test it so not sure pix will illuminate anything. Standard NTK brand 5-wire sensor. I *think* I may have salvaged it based on the output voltage results (compared to numbers from a known good sensor)

I did buy a 'new' O2 sensor off eBay but the bench test showed an internal fault. Still trying to get refund. If you want to see the test, here is a youtube link:
http://www.youtube.com/watch?v=iXPdhai_5iE

NOTE: This test is with a known good sensor from my other VX ('95) which runs like a top. (just got this one in March but have to fix rust on it)

[92VX]

I had an oxygen sensor that tested good on a bench, like your test, but wouldn't work for squat on the car. Changed to a new one, problems went away. I don't know if you tried the one off Ebay, but I would regardless of the bench test. That being said, I believe the ones off Ebay with a blue wire have been known not to work on the VX. That's why I asked for a picture of wiring.

If you do have a coolant leak, it won't effect the O2. Unless it's like dripping directly on it.

I think the ultimate test would be to take the O2 sensor you first had on the car and plug it into your '95 VX, see how it runs. This way we can rule out the sensor.