O2 sensor test resuts
 

Finally got around to it to see why I only get 270 km/tank fuel economy. Started cold at ~.2vdc. As it warmed it rose to around .6 but then started to quickly fluctuate between .7 and .15. I would think it was switching back and forth between open and closed loop. When it dropped the engine idle increased.
Anyone see this before?

This behaviour is as expected. Your O2 sensor is probably OK. The sensor is ment to alternate voltage like that.

Doesn't sound right. A passive device that uses somthing like a crystal to output a small voltage varying on temperature should not jump like that? How would the computer read this and vary the fuel ratio based on somthing jumping all over the map?

My highway fuel mileage has dropped from about 30 to 22-24 range on two tanks. My O2 sensor puts out .55 V when cherry red and takes a long time to drop off when I remove the torch from it. It also takes a long time to reach .55 V when heating up (like almost a minute). I understand 0.55 V is a little on the low side. New one should be in Tuesday so I should know something in two weeks about mileage. Town driving also dropped from 24 to around 19 mpg. Plan to test the new one before putting it in the car.

O2 sensor voltage should vary by a minimim of 0.5v ..in other words from about 0.25 - 0.75v.
Yes, it does and should fluctuate. If it doesn't something is wrong.
Usually, if stuck on 0.45v the sensor itself is dead.

Your sensor is working properly.

The "jumping" you see is actually being caused by the DME.

The DME "reads" the O2 sensor and adjusts the injector duty cycle (Open/closed times) to that the AVERAGE sensor output corresponds to a fuel/air ratio of 14.7:1.

To get a better idea of what is going on, start off with the sensor disconnected from the DME. If you have a late model (85.5 and later), disable the idle stabilizer as well. Once the sensor is up to temperature, with the engine at idle you should see an output in the 0.60 to 0.70 volt DC range.

If the voltage is too high or too low, adjust the by-pass on the Air Flow Meter. When you make your adjustments you may need to adjust the idle by-pass on the throttle body to maintain a proper idle RPM.

Lawrence:

Your "test method" is not correct. The sensor needs to be in the engine exhaust, not the flame from a torch.

Cliff:

What I did is pretty much a standard method of testing according to numerous sources I have found. Why should one believe you when there is only one of you and countless other sources underwriting the out of vehicle torch test?

whoah, now, lets keep it friendly.

Just asking a simple question. Why does he think he is correct and many other sources are wrong? Nothing unfriendly, I just want substantiation of his claim that contradicts general thinking.

Do a google search on oxygen sensors, then do a search on results with the word 'testing'. Read the links.

My new oxygen sensor arrives today. I'll do the same test with it and post results later.

To test an oxygen sensor, you need to get it good and hot, and expose it to known oxygen concentrations.

You can't do this in your own garage.
Using a torch will tell you (if your O2 sensor is perfect) how efficient your torch is, and how much residual O2 is in the exhaust of the torch.
Not going to tell you a lot about whether it is good.

If your O2 sensor was connected when you got those readings, then it's perfectly healthy. If it was disconnected, I would be checking for vacuum leaks and such that would cause the DME to be constantly adjusting the mixture.

Yeah, physical devices don't pay much attention to opinion poles.

Mainly because I have been working on internal combustion engines for over 40 years, and I know what the f#$% I'm talking about.

Got the new sensor in the mail and performed the same test with the torch. Instead of taking about 50+ seconds to reach 0.55 V and being very sluggish reacting to torch movement, the pristine one reaches 0.9 V in about 6 seconds and is fast to react. Old one reacted at a snail's pace.

We shall see about the mileage once I get around to installing it. The torch test certainly tells whether the sensor is dead or not. So I guess in mathematics terms, it is a necessary but not a sufficient condition.

I don't think oxygen sensors have been around for 40 years. My '71 Ford did not have one......my '80 Mercedes Roadster was the first car that I owned that had one.

still stirring the pot, i see.

Not trying to stir it. I indicated in an earlier post that I would report similar test results on the new sensor when it arrived. I did what I said I'd do. The new sensor clearly responds with more alacrity and magnitude than the old one did when tested. As to whether my fuel mileage will return to what it was has not been determined yet.

There was one other change made to the engine. I installed a new idle stabilizer valve. Previously, the engine would not idle properly when cold. Plugs were rather sooty/oily but mileage was very good. I replaced the ISV and drove car to Atlanta and back. Mileage was much less but cold idle is fine. Plugs, to my utter chagrin, were no longer sooty/oily and had that nice sandy color. But fuel mileage is now in the toilet.

Should find out something this weekend as another trip is planned.

Dude, we are all friends here and if you are going to stick knives in someone's back, I'm not sure anyone wants to read your posts so really, just don't bother. If you want to be kind and helpful, that's different. Read the responses, we can't all be wrong. The problem is you! Lighten up or don't even bother asking for help. Advice here is free and you don't have to take it if you don't want, but don't jump down someone's throat because they are trying to help you. What are you trying to accomplish by shooting bullets at everyone?

good lord people. can it, already.
one member says he has a test. great. it's documented elsewhere that this test is valid.. whoopie... then someone else in the school yard comes and tells him his test is wrong... the original member posts his results of a new sensor using his method.

big deal?? what is all the fuss about?
some people test 9V batteries by licking the terminals.
if the test works for the individual, great. If it doesn't work for you - move on.

be mature.

I'm not going to try to lick my coil wire to see if the coil is working. Concept probably works though.

Harvey

tastes like chikin!

That's like my friend, he was trying to figure out what cylinder wasn't firing on my 951, so he was pulling the plug wires 1 by 1 (At the cap, while the car was running). Somehow he was surprised when he got shocked.....

New sensor has been installed. Should have mileage results sometime next week. Engine seems smoother but that could be psychological. I strongly suspect my problem of poor fuel mileage is going to be solved and the problems was, indeed, a sluggish and low output sensor caused by fouling.

What output sensor? Do you meen the O2 sensor?

Yes. should have typed oxygen sensor rather than output sensor.

Lawrence, would you recommend changing out old O2 sensors by default of age/milage even if there doesn't seem to be poor gas milage or outstanding issues? I'm thinking about doing this because I have no record of them not being original.

i wouldn't...
remember the porsche saying - if it ain't broke, STAY THE HELL AWAY FROM IT! :p lol

I would not change it unless mileage drops off. Mine had been in car since 89K when I bought the car. I could not figure out why the mileage had dropped on my car. If I did not have the drop in fuel mileage, I would not have taken it out, tested it, and replaced it when it failed the test. I tend to leave "well enough alone". Jury is still out because I have not used a tank of gas yet, but I rather confident about the fix.

I've read stuff saying the sensor should be changed every 30k miles. But the article was written by Bosch. They have a conflict of interest and would like everyone to change their sensor every 30K.

We had a sedan that we put 140K on before trading it. It's mileage never fell off and I never changed its sensor.

Mileage Results
 

Well I finally got around to doing a mileage test with the new oxygen sensor. I missed my February trip due to snowy weather. The mileage had dropped off from around 28 to under 25 on the standard trip I make to Road Atlanta. Just filled the car and it got a little over 29. It had gotten about 24 around town when I filled. Before the new sensor, it had dropped off to 19 around town.

So, my conclusion is this: the poor mileage was due to a sluggish oxygen sensor. Mine was so bad that I was able to pinpoint the problem with the blowtorch test. Incidentally, propane is a carbon-hydrogen molecule. Its chemical formula is C3H8. Octane is also a carbon-hydrogen molecule, C8H18. Larger but the same basic elements.

Since my mileage is great, I will assume that my O2 sensor is still OK.

Harvey

Okay, but the fact that you are burning a hydrocarbon is virtually irrelevant. The O2 sensor once heated acts as an oxygen-concentration comparator.


That said, about 80% of the time bad mileage problems are a bad O2 sensor. Good to hear you got your problem fixed :)

I encourage changing them every 4-5 years if there are no mileage problems, sooner if there are. The reason being once they start to go bad, you start to get carbon buildup on piston crowns, etc. Things that can continue to cause problems once you change the O2 sensor.

I'm tickled the mileage returned to where it was. Plugs look really good too. Before, they were sooty.

If you get the Bosch universal one, it costs about 1/2 of what the one with the special connector. It's the same sensor, just no union that plugs in. You have to splice.

The cheapest I found was for a ford, maybe a tempo?...
It was $23CDN for a 3-wire O2 sensor. I had to use my own butt connectors, but that's no big deal. That said, the universal was second-cheapest. And the proper Porsche-fitting one was about 4x more.

Sounds about right for the Ford part. I've used three of em in three different cars and had excellent results.

Do you happen to recall the part number?... Because I don't.
I used to have a friend that worked on the store, so he just brought up like 100 of them and scanned them all until we found the cheapest, I don't think anybody else there would do it, lol.

Bosch part number 13913. Universal type 3-wire. $34.99 on sale at Advance Auto Parts.

Is the universal for any car or specific?

For any car that takes a 3-wire sensor.

Does anybody know the ford part number?