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[StealthGP]

I just changed my front 02 sensor. I've been fairly certain it’s been failing for a while now because it seems like its been running very rich. Noxious exhaust fumes, black soot collecting around the exhaust tips and shitty gas mileage, but otherwise running fine. My narrow band A/F gauge never indicated right since I installed it, always showing full lean (which makes sense because it the sensor was bad and showing lean, the PCM is going to richen up the mix). Because I don’t have a rear O2 sensor hooked up, the check engine light is always on so it wouldn’t be immediately clear to me if the front O2 sensor was setting a code. I hooked up the scan tool, and sure enough, it was showing a code for a defective front 02 sensor. I bought a new Bosch sensor to put in.

When I crawled under the car, I noticed the headers were leaking quite a bit at the Y-piece, so I bought some heavy duty band type clamps to seal it up. When I removed the old 02 sensor, I could see that the wires had burned because they had touched the downpipe.

Start the car up and the gauge begins working like it should, showing its running stoich. I drive it and….it runs like crap. From a stop it’s got no power and acts like its going to die. I hold the throttle steady, then all the sudden it takes off. Cruising, the RPMs fluctuate from almost ready to die, to surging forward. At idle, RPMs fluctuate up and down too, enough that the lights dim. And all the while, the A/F gauge is showing everything’s perfect.

I hooked a scan tool up, and while it shows at the moments it seems like the car is going to die, the 02 sensor voltage drops down a little bit, the long term fuel trim flatlines at -25 and stays there (Over 20 frames, O2 sensor data min. is 0.52v, max. 0.70v, and averages 0.63v). I pull the codes again and it shows: P0030 - H02S Heater Control Circuit Bank 1 Sensor 1 and P0135 - 02 Heater Circuit Bank 1 Sensor 1, in addition to the rear 02 sensor codes.

Sound like my replacement sensor is bad out of the box? Its just seems odd that the gauge shows all is well, and it’s only showing codes for the 02 sensor heaters, not the sensor itself. And the voltage is somewhat stable, but the fuel trim bottoms out. One more thing I noticed…the gauges continues to show stoich even when the engine has been shut off. Maybe the 02 sensor is just putting out a near constant voltage all the time instead of actually working as a sensor? I’ve got another Bosch sensor and a Nippon-Denso sensor on order just in case. I’ve got the scan tool data if anyone wants to see it.

[06 IBM GOAT]

dont use bosch , use denso

you using the plug in extension i sent you ?

[StealthGP]

Yeah. Thats the other thing. The original sensor I replaced had the sections of wire spliced in to make it long enough. When I put in the new sensor, I removed all of that and used the extension.

I'm kinda iffy on Bosch. I've had lots of people tell me that Bosch 02 sensors aren't very good, but I sell them all day long and never really get any back (I do get lots of people coming in to get a set of Autolites or NGK's because the Bosch spark plugs they just put in their vehicle made it run like crap though). But thats why I ordered the ND. They seem to have a better reputation. If the ND works and the Bosch doesn't, I'll advice my customers against the Bosch.

[StealthGP]

Here's a graph of throttle position, load, LTFM, and 02 sensor voltage over 20 frams. You can see how the fuel trim flalines out.

[StealthGP]

New sensor still doesn't come in until tomorrow. I just unplugged the front sensor (so now it has no O2 sensors) and it runs much better.