I think that my o2 sensor is toast. It reads about 0.5V when fully warm, but voltage does not increase if I blip the throttle or if I increase the throttle gradually. In fact, the voltage actually shows that it is dropping off when I do that.

How far back is the O2 sensor? Does the belly pan have to come off for me to splice in a new one?

 

to replace the O2 sensor you have to drop the pan and the cats.

.5V means it is running at stoich, less volts = lean. shouldnt jump about too much either. when was it last replaced though?

 

About three years, I believe. Workshop manual says that voltage must increase if you depresss accelerator.

Unless something else is causing a lean out situation and the O2 sensor is giving me a correct reading????

 

It should read a high voltage when you blip the throttle, due to the transient enrichment the LH ECU makes when it detects the fast change of MAF voltage....... are you reading that voltage with a multimeter, or reading from an LC-1 or similar ?

 

It requires a fairly good quality multimeter to track the variances in an O2 sensors output .... better if you have one with an x-y plot of voltage vs time. My Fluke meter will track OK, but the garden variety digital meter that I don't mind dropping is too slow in response to give more than an average of 0.5v.

 

I have a radioshack multimeter. i don't imagine it is very high quality.

It does give new readings, but they are the same or lower voltage levels.

I just did another test. The voltage varies when I move the throttle. It does not move much up or down from the 0.5V reading, however. Even when I rev the engine to 3 or 4 thousand rpm and let it drop, or rev to 3 or 4 thousand and hold it there, it stays near the 0.5V. It will fluctuate up or down by 0.05 V.

 

to run that test you really need a analog VM.

 

The LH responds to changes in throttle position and load by slightly richening the mixture. It's the rate of change that's important. Gently reving the engine to 3000 RPM with no load may not make a noticeable change in sensor readings, since the brain responds to the sensor input and normalizes the mixture to get that 0.5v. Hard throttle blip should result in a slight rise that may not show up on a meter that's a little slow to update.

The graphing Fluke is a good meter for this but might be just a little spendy for just the car work. Of course, I've been known to drag the o-scope out for chasing stuff like this too.

New sensors are too cheap to mess around with IMHO. I used to figure that 20-25k miles is about the breakover point on sensor costs vs gas saved. Since then, sensors have gotten cheaper and gas is more expensive, so if there's any doubt about a sensor that's been in there for more than 25k, just replace it.

 

I hear ya. It is not the price of the part, it is the pain in the *** (or back) under the car changing it out. I don't have a lift and I will be flat on my back to do this. I would rather test out the part and know or feel a level of confidence that it is bad before I tackle this.

What about the cheapo analog multimeter at radioshack. It should do the trick, right?

 

yes the analog meters dont have a delay in showing the info, it should respond to the voltage exactly how it sees it. will be harder to read though.

 

I don't have a lift either, but didn't think changing the oxy sensor was that tough. I do have tall stands, and believe in using them for the broad footprint at least as much as for the extra height.

Header pipes unbolt from the manifolds, and the brackets to the bellhousing bolts come off. A regular stand goes under the front of the pipes so they just come down enough to access the sensor.

Wire runs through a grommet on the top pass side ot the center tunnel, to run across the front edhe of the central electric panel to a connector. So unplug the old one, feed the cable back through the hole after you get the grommet through the hole, then slide under and get the cable down and free. You can use a universal 3-wire sender if you don't mind doing a little soldeing and splicing. The heater connects through the two black wires, and they can be soldered and heat-shrinked OK. The white signal wire supposedly draws its reference air in through the wire inside the insulation, so Bosch recommends that you use a butt-style crimp connection for the signal wire. Try to make the connections far enouh towards the end of the wire that the splices will be well inside the car, protected from weather and water.

Whole job is less than an hour including getting the car up and down on the stands.

 

I understand that the heater is not required. What if I just but connect the signal wire. Any probs?

Thanks for the advice, by the way.

 

Didn't know about that bit with the air through the wire. Sounds kind of flakey.

Be extra careful about routing these wires. IF they are too close to the exhaust you can cook them and short them and you'll be dead in the water. The voltage supply comes from the same relay as the fuel pump, so you'll lose them both.

 

The heater isn't "required", but unless you are really so poor that you don't care to spring the extra few dollars for the heated sensor, do it like you mean it and get the right sensor. The heated sensor gives valid CO readings much more quickly, so the car is likely to run better and cleaner for the first few miles when you might otherwise be waiting for the exhaust system and the sensor to get hot enough. With the senor cold, the system typically faults to full-rich due to the low signal voltage. If you are a shorter-distance driver, the extra fuel may eventually cause oil dilution. You may not need to worry about that, but maybe the clean air part is an incentive of sorts. Reality is, once you are in the pass footwell splicing wires and stuff, the difference between one and three connections isn't more than another couple minutes.

On the "reference air through the wire" claim from Bosch, I wasn't aware of it and went ahead and soldered everything. Seems to be working OK.

 

Hi Cameron,
If you are going to try another meter, use a digital multimeter with a "peak hold" function. That should show the transient responses from the average.

I am afraid that the "reference air through the insulation" must be a translation error !

Would strongly advise a heated O2 sensor.