O2 sensor replacement - ambitious for newbie?
 

My car is hunting at idle and I spoke to a mechanic and he suggested that the O2 sensor should be replaced. I do not have experience with fixing cars however I am very keen to learn and have had no trouble picking up other skills (eg home renos). It looks like the sensor replacement is pretty straightforward. Is this a reasonable thing for me to try?

Cheers

Pretty easy but the sensor can be tough to get out depending on how long it's been there. My 95 911 came out pretty easy but the 89 944 required the exhaust to come off so I could get a BIG wrench on it.

+1. It could be easy or hard depending on how seized the sensor is into the exhaust. Give it a try and if you can't get it, then you can take it in to someone. Won't hurt to try.

Not sure if spraying penetrating oil on an O2 sensor would damage the sensor at all, hopefully someone else can chime in on that. I guess if you are replacing it with a new one anyone then it won't hurt. Soak it with the exhaust cold for a day or so, several applications, then give it a try. PB-Blaster is my penetrating oil of choice, available at your FLAPS.

.that's internet car forum speak for "Friendly Local Auto Parts Store" for a NooB. :)

Hello fellow canuck (and briefly a "Pegger" actually),

An O2 sensor change is a sinch, I did one for the first time yesterday. I ended up using one of the less expensive alternative sensors and it seems to work fine. The engine runs well and no more idle fluxuation. I used the NGK 22014 available at NAPA for $70.00. To get a none Porsche sensor to work you will have to splice in the new three wire sensor to the old 911 plug.

Replace the old and new sensor using a 22m wrench. Mine was a little tight so I soaked with penetrant oil overnight and it came off just fine the next day. Just remove the left rear wheel and there is easy access. The three wire plug is on the left side of the engine compartment.

Thanks guys. I think I will give it a go.

Pelican offers a "universal" O2 sensor for $71 and another for $134. What's the difference? Both are made by Bosch.

I really want to become hands-on with my 911.

Cheers

Ps - Nick, thanks for the noob translation!

the more expensive one is a plug and play. just disconnect the plug in the engine compartment by the fuel filter. the cheaper one is the one you have to splice. advanced auto online has the bosch plug and play for $93 shipped and no tax. i just did mine with a cat delete.

If you are serious about this, don't spend the $$ for the fancy O2 sensor.

Buy the universal Bosch and with the money saved drive to an electrical supply store and spring $20 for a set of Channel Lock wire strippers and ask them to provide you with crimp connectors. Better yet, solder the wires together and get some shrink wrap tubing to seal off the connections.

Also, buy a nice digital multi-meter. You don't need a Fluke but a spend north of $75 will get you a solid tool you will not be able to live without.

Watch youtube videos on how to use a multi-meter. It ain't rocket science but you don't know what you don't know.

http://www.quill.com/channellock-wire-strippers/cbs/257355.html?Effort_Code=901&Find_Number=701079ORS& promoCode=460460055

I think the sensor wires can not be reliably soldered. IIRC, either the heater or sensor wires must be crimped.

Hunting idle can be caused by so many things.

I wish I knew 'lectricity better.

Ack! Sorry, I want to clarify that some of the wires are steel. I just can't recall which ones. I think it's the two heater wires that need to be crimped.

Thanks for the additional input. I realize that I have a *lot* to learn. To get started I think I would prefer an easy approach just to get my feet wet.

Rusnak - I've read a number of threads on hunting during idle and I realize that there could be other reasons why that's occurring. I thought this would be a reasonable place to start. I may come back for more advice!

Thanks again.

You can buy a Bosch three wire O2 sensor for a 96 Ford Taurus at your local FLAPS for less than $20. Cut of the connector and splice that into you existing engine side connector. Crimp and heat shrink. No solder.

Stagger your crimps so you don't have them in a big lump and you can reuse the factory protective sleeve.

Lay the new and old sensors out on the bench when you make your cuts to keep your overall length close to factory. Use a little soap or windex to lube the grommet and it will slip into the engine tin easier.

Some of the aftermarket pre-mufflers move the O2 bung further away from the hole in the engine tin. If you are headed that direction now is the time to add a couple of inches to the bottom half of the harness.

-J

Was serious above - no sarchasm. So much I don't know about cars and their electrics.

When I find a problem that seems complex, it ends up being brutally simple. But in this case I assumed it was simple and there is more to it. i.e., Different type of wire. (My 81 still has the single wire)

Also, when I wrote the above I was thinking about my cyl head temp sensor I installed on my 81 and how you are not supposed to shorten the leads to the dash gauge. My immediate thought was that some of the wires in a three wire sensor might be based on that principle - (resistance?)

I often fix cars for folks that have O2 problems and I still have not taken the time to really study the more modern systems so I can test them effectively. I have been lucky and not wasted money on one I did not need to buy but it usually came at the cost of eliminating other variables - which is costly.

So any-hoo....Sorry Colin, for rambling. Do take time to study the basics on a multi-meter. It will be your new best friend. If you couple the knowledge with info you can gain here through searches you can be a fixin' stud. It is really gratifying to nail a gremlin through diagnostics.

Make sure your O2 sensor is really the root of your hunting problem. If you disconnect it and your car stops hunting, then the sensor is the problem and needs to be replaced. If it still hunts after disconnecting, it might be your fuel mixture and you need a CO analyzer for that.

Another easy way is to use a hacksaw or zizzwheel, cut the sensor flush with the nut and use a deep socket. 22MM or 7/8. You can get a lot more torque on it that way.

http://www.clarks-garage.com/shop-manual/OxygenSensorInstall.pdf this might help, not your exact application but you should figure it out

Mine was a little tight so I soaked with penetrant oil overnight and it came off just fine the next day.http://www.sioauxzc.info/5b.jpg

If you have a hunting idle, I'd suggest checking for vacuum leaks first. Vacuum hose is pretty cheap, so it certainly wouldn't hurt to replace if it doesn't flex easily or is cracking.

O2 sensor replacement is easy. Jack up the driver's side of the car, 22mm wrench. The universal O2 sensors are a cheaper way to go, but solder the connections with silver solder. The universal Bosch sensors come with this Posi-lock box looking thing, but it's given me trouble in the past.

Thanks for the input. I'm certainly going to consider all of your comments.

Bob - no worries about rambling. I'm lecturing a genetics course right now and my students could verify that I ramble pretty regularly!

Cheers

I've spent untold hours reading threads in this forum over the past few years. I've had my '84 since December and have been reading here even more since buying it, soaking up the vast amounts of knowledge and experience. My mechanic buddy and I did the 60K service and the O2 sensor at that time. (Sensor replacement called for every 60K miles.) My idle hunt (slight) and slight 'jerky' issues seem to have been cured by replacing the intake gaskets and spacers. My buddy squirted water around the intakes and sure enough, the idle stumbled on one port. New gaskets and spacers seem to have done the trick in my case. For now! Runs and drives like a dream.

Oh, and I have the Pelican O2 sensor tool but I seem to think that it wasn't needed when I removed the original. Car on stands, LR wheel off, heat shielding removed and it was right there and easy to remove. hardest part on my car was the broken upper O2 sensor plug which may not be a problem on your year.

No offence, but this is not 100% accurate (I know from experience) as a "too rich" condition can cause a hunting idle situation even if the O2 sensor is good - disconnecting it simply takes the O2 sensor out of the loop, but does not prove it is bad.

Ronnie - so disconnecting the O2 sensor would make the engine run leaner? What you're saying (if I understand you correctly) is if this appears to solve the problem this doesn't necessarily mean the O2 sensor is bad? I think it is running rich but I have no data to support that.

I'm in the process of accumulating some tools and courage.

Cheers

Colin - I am only familiar with the K-Jetronic (CIS) fuel system and I think your 86 has Motronic, correct? If so, perhaps what I am saying doesn't apply to your car. . .

With the K-Jet system, the O2 sensor reads the oxygen content in the exhaust and then the system attempts to compensate for a rich condition - this can lead to a hunting idle. When the sensor is disconnected, the K-Jet frequency valve goes into a fixed duty cycle (no longer trying to compensate) - so the rich condition is still there but the idle no longer hunts.

Again, this might be apples to oranges for your fuel system . . .

And of course, the only negative consequence of experimenting with replacing your O2 sensor, is you might find you didn't need to, and that is definitely not the end of the word (not a $$$$$ part, in other words).

I thought the "no soldering" edict was odd the first time I read it, so researched it a bit.

The O2 sensor needs a reference for "fresh air" - which it apparently gets by sucking fresh air down the center of the wire. If you solder and heat shrink the splice, this will block the path of fresh air. So it will then have no reference.

From the Bosh document for the LM11 http://www.bosch.com.au/content/language1/downloads/sensors_oxygenlsm11.pdf And


The wire is stainless steel for "resistance to corrosion and thermal stress", according to that document.

But the installation instructions (page A-28) do describe installing via the supplied posi-lock connector - and go on to state

So a little update. My idle is pretty high (1000-1100) rpm so I realize that's an issue. However, I started it up today and got a steady idle at about 1000 rpm(sometimes it surges right from starting sometimes it doesn't) and I tried the oil cap trick to see if the rpm would drop. It did. I replicated it several times and each time the rpm dropped about 100 rpm or so. That said, there is a hose that puzzles me (this will really show my igmorance!). The part just before where the air splits into the two intake manifolds there is a hose that exits towards the front of the car (about 1cm in diametre) that is not connected to anything. It is plugged with a bolt and there's a hose clamp keeping it in place. The free end of the hose is kept in place somewhat loosley by a cable lock that's going around one of the hoses that goes into what I think is the ICV (but the hose in question is not hooked up to the ICV). Anyway, it looks weird.

Cheers

Oddly, after I did the "oil cap test" my surging problems seem to have disappeared. Over the past two days I have had a constant idle. Weird, eh?

If you suspect the O2 sensor is causing idle hunting just unplug the O2 sensor. These engines run fine with it unplugged. The O2 sensor and it's circuitry are only for minor mixture fine tune. The actual procedure to set mixture is with the O2 unplugged.

Idle hunting is usually the result of an air leak or improper mixture settings. So eliminate the O2 sensor from the equation by simply unplugging it.

Also be sure that the idle switch on the throttle body is working. If the switch does not close when the throttle plate returns to the idle position then the DME (computer) will not enter the idle maps.

And if you plan to cut and splice the O2 sensor wire be very aware that the green signal wire is a shielded wire with a center conductor and an out braided shield. I worked on a car a few years back where someone decided to splice a after-market O2 sensor and they soldered the center wire to the shield! The end result is that they effectively grounded the signal line which tricks the DME to always see a lean mixture and then the DME just richend the &*^$ out of the mixture! It was impossible to set the base mixture! Took me 8 hours to find the problem!

I had a similar problem with my 84. I replaced the O2 sensor, but it didn't fix the problem. Then I had my mechanic adjust the mixture. Problem solved.

You might consider a mixture adjustment before throwing parts into the car. Easy (and inexpensive) fix.

HTH.

Scott

I have an LM-1 air/fuel mixture gauge. It reads out in % Lambda.

What you will notice is that the "mixture adjustment" is taken over by the DME/ O2 sensor once the sensor heats up. All you're doing when you "adjust" the mixture is setting the baseline further or closer for the DME to adjust.

I think a faulty or worn O2 sensor is a very logical diagnosis when the mixture can be measured and is clearly rich. If lean, then you'll be suspecting either a huge vacuum leak or fuel delivery issues.

Surging idle is caused when the DME is trying to adjust fuel mixture with fuel pulses, but is stuck in a faulty feedback loop, such as a false air or vacuum leak. Or the mixture is outside of the DME's ability to correct. "Adjusting" the idle merely re-sets baseline. You'll be at this baseline when your O2 sensor is unplugged or the O2 sensor is cold. Of course, the pre-programmed map is also in effect too.

My problem with unplugging the O2 sensor on a US car is that the system is still searching for voltage from that wire. Any stray voltage can trick the DME into thinking that the car is running lean.

I've done tons of tuning on the Factory DMEs and know first hand that surging idle in these engines is almost always a result of rich base mixture. I know this because I can easily force this to happen by just enriching mixture at idle, I can do this on the fly with my EPROM emulator and my laptop. It also does not need to be off by much to cause the issue. Base AFR below 13.8 often causes this issue especially at cold start.

You can even try a test yourself by simply unplugging the CHT sensor shortly after cold start. When you unplug the CHT sensor the DME sees (thinks) extremely cold CHTemp and instantly richens the mixture well below AFR=13.0 and the engine should immediately start surging.

I suggest a very simple adjustment, on the AFM turn the air screw out about 1 turn (keep track of the original position so you can put it back) with it out 1 turn you will have leaned the idle mixture and the surging may go away. But the only way to properly set base mixture is with a CO meter or a WideBand O2 if using the WideBand target AFR=14.2 at idle.

Rus, this is not really the case. The DME circuitry does not just simply float this signal when the O2 is unpluged. The signal line has several resistors built into the circuit and the end result is the O2 signal line goes to about 5vdc via a voltage divider created out of a few resistors. Once the line goes 5vdc the DME program code completely bypasses the O2 closed loop code. The Euro DMEs work with excatly the same code as the US DMEs but the Euro DME simply hard wires this input line to 5vdc.

Bottom line is that if you unplug the O2 sensor in the US DME it runs just like a Euro DME without an O2. The only thing that could happen in a US car is that somehow the O2 signal line get accidentally grounded. So long as the O2 line does not get grounded by accident then the DME runs fine.