5th O2 Sensor this year!!

[xclusivecar]

Replaced all 4 O2 sensors over the last year...then the MAF...then 1 Cat...and now ANOTHER O2 sensor! After questioning the Porsche mechanic as to why this is happening, I am told that Porsche has had a bunch of problems in the winter with the reformulated fuels damaging the O2 sensors. He also states that Mercedes is also having similiar issues with its AMG engines.

Now, this somewhat makes sense since I DID NOT have any troubles this past summer. All troubles have been during the past 2 winters.

He summarizes by telling me I need to OCCASIONALLY gas up using 87 or 89 octane. This would somehow force the engine to "clean" itself and all emission components downstream. Then go back to 92-93 octane for several tanks and continue this throughout the winter and until summer blend gas is back.

Does this make sense? or...am I being led?


The car is a 2000S

[blue2000s]

It's BS. Go to a different mechanic who can actually fix your problem.

[Darkhamr]

I'm not sure what specifically could cause the O2 failures, but perhaps sticking with a 'Top Tier' supplier might help.

http://www.toptiergas.com/retailers.html

[Cloudsurfer]

I can't possibly see what your mechanic claims 87 octane would do for your motor, aside from cause problems. While there are differences in winter blended fuels (in those parts of the country where it does get cold), ad that could hypothetically cause issues with certain motors (never heard of this directly, but it could be plausible), running a lower octane fuel to "clean" an engine is ridiculous. All that would do is force the engine to run greatly reduced timing to control knock, limiting performance, and making the DME re-learn how to operate on the proper fuel once its given it, and may or may not cause serious damage in the interim.

What may contribute to your 02 sensor issues during the winter is the longer time it takes things to heat up from a cold start, which would cause increased deposits to form on the sensors.

I'd also consider looking for a new mechanic.

Patrick

[porsche986spyder]

Why not just use a good fuel injector cleaner once in a whie?

[blue2000s]

Originally Posted by porsche986spyder

Why not just use a good fuel injector cleaner once in a whie?

His problem isn't fuel or clogged injectors, it's a mechanic who's replacing things that aren't broken and either not willing or not able to really fix the problem.

[blue2000s]

Originally Posted by bmwm750

I can't possibly see what your mechanic claims 87 octane would do for your motor, aside from cause problems. While there are differences in winter blended fuels (in those parts of the country where it does get cold), ad that could hypothetically cause issues with certain motors (never heard of this directly, but it could be plausible), running a lower octane fuel to "clean" an engine is ridiculous. All that would do is force the engine to run greatly reduced timing to control knock, limiting performance, and making the DME re-learn how to operate on the proper fuel once its given it, and may or may not cause serious damage in the interim.

What may contribute to your 02 sensor issues during the winter is the longer time it takes things to heat up from a cold start, which would cause increased deposits to form on the sensors.

I'd also consider looking for a new mechanic.

Patrick

The sensors are self-heating. They wouldn't have this problem.

Eclusivecar, what Porsche dealership is telling you this in the Chicago area?

[Cloudsurfer]

I am aware the sensors are self heating, but correct me if I'm wrong, unless you instert the key and turn to on and give it 15 sec to heat the sensors, you are still firing the motor with them cold. Granted, this may be splitting hairs and I was simply trying to explain a point likely unrelated to his problem, but worth noting nonetheless.

Patrick

[MNBoxster]

Hi,

It's absolutely a possibility. Winter fuels are rich in Butane and Oxygen because they are cheaper than adding other Octane boosters such as MBTE, Alkylate, and ETBE.

Because the need to meet RVP (Reid Vapor Pressure) mandates by the EPA lowers due to winter temps (allowing the use of Butane and Oxygen and still meet mandated RVPs), refiners switch to Butane and Oxygen in greater amounts (because it is cheaper to produce). This can trigger a CEL because the values lay outside the DME's pre-programmed O² Sensor values.

Since lower Octane fuels require a lesser concentration of these chemicals, they will prevent a CEL from occuring and the concequent defaulting of the DME.

Because the ambient temps are considerably lower during this season, the detonation threshold is also reduced. You may actually be OK using these fuels and the sensors will return to normal operation in the Spring. In theory the guy's correct, but in practice? Only making the switch will tell...

Happy Motoring!... Jim'99

[SigmaPi]

If that is true about the O2 sensors being sensitive to fuel mixtures, why has it not affected my Lexus or 4Runner in the same manner? Porsche is obviously a superior product right?

[MNBoxster]

Originally Posted by SigmaPi

If that is true about the O2 sensors being sensitive to fuel mixtures, why has it not affected my Lexus or 4Runner in the same manner? Porsche is obviously a superior product right?

Hi,

Not at all. It could be construed that Porsche is inferior. It's not the O² Sensors, but the software limits of the DME. It does not have any Maps for the readings the sensor is sending it - the values lie outside the defined operating parameters.

Your other cars may well be affected, just not to the same degree. The ECU has an adequate Map to cope with the circumstances and so doesn't foul the O² sensor or send a code...

Happy Motoring!... Jim'99

[blue2000s]

Originally Posted by MNBoxster

Hi,

It's absolutely a possibility. Winter fuels are rich in Butane and Oxygen because they are cheaper than adding other Octane boosters such as MBTE, Alkylate, and ETBE.

Because the need to meet RVP (Reid Vapor Pressure) mandates by the EPA lowers due to winter temps (allowing the use of Butane and Oxygen and still meet mandated RVPs), refiners switch to Butane and Oxygen in greater amounts (because it is cheaper to produce). This can trigger a CEL because the values lay outside the DME's pre-programmed O² Sensor values.

Since lower Octane fuels require a lesser concentration of these chemicals, they will prevent a CEL from occuring and the concequent defaulting of the DME.

Because the ambient temps are considerably lower during this season, the detonation threshold is also reduced. You may actually be OK using these fuels and the sensors will return to normal operation in the Spring. In theory the guy's correct, but in practice? Only making the switch will tell...

Happy Motoring!... Jim'99

If it were sensative to this, it would be a widespread problem with all Porsches. It would also not be helped by switching to a lower octane fuel. I don't believe this is his problem.

[Tool Pants]

I think Bosch has crappy oxygen sensors, or a bad batch. I have replace 1 sensor 3 times. The sensor after the cat on the passenger side. The other 3 are the originals on my 1997.

Our smog inspection is every 2 years. Every 2 years I have to replace the same sensor that was replace 2 years before.

In March it is time for a smog inspection again. And again I am getting a check engine light because of that same sensor.

There are a lot of good theories in this thread about sensors going bad. In my case I do not see how the theories would apply.

The shop foreman has been a friend for 8 years and every 2 years at smog time we go over this issue while my car is hooked up to the PST2/PIWIS. He checks my car before I go on the smog machine. If that sensor is acting up again then it is replaced and then I go on the machine and pass.

[MNBoxster]

Originally Posted by blue2000s

If it were sensative to this, it would be a widespread problem with all Porsches. It would also not be helped by switching to a lower octane fuel. I don't believe this is his problem.

Hi,

Never said it was his problem, just that the guy's theory was credible. It may not appear in other models because they use a different software version and/or different Maps for their specific application.

If this were actually the problem, switching to a lower Octane fuel would have a positive effect. This is because the MBTE, EBTE and other compounds are primarily added as Octane Boosters. As these are replaced in the Winter by cheaper Butane and Oxygen, the concentrations of these compounds is less at lower octanes where the need to add boosters is not so high. Lesser concentrations = less stuff in the exhaust which the Sensor/DME doesn't like and could remain below the problem threshold. It won't hurt to run a tank or so of lower octane fuel, won't grenade the engine, only over the long term would you be risking anything...

Happy Motoring!... Jim'99

[xclusivecar]

Thanks all for the input...I only lean toward the "its the winter blend" theory because I ONLY need to replace a sensor in the WINTER. Never have I had to replace one in the warmer months. All 4 of mine were replaced last winter...I went the entire spring,summer,fall, with no problems. Winter hits this year and BLAM...I needed a new Cat and after that was replaced another O2 sensor went. Coincidence????

I will try the lower octane stuff in my next tank knowing that it will not hurt the engine...only performance. But thats OK...it is winter and I'm not exactly flying around these Chicago roads!

[blue2000s]

Originally Posted by xclusivecar

Thanks all for the input...I only lean toward the "its the winter blend" theory because I ONLY need to replace a sensor in the WINTER. Never have I had to replace one in the warmer months. All 4 of mine were replaced last winter...I went the entire spring,summer,fall, with no problems. Winter hits this year and BLAM...I needed a new Cat and after that was replaced another O2 sensor went. Coincidence????

I will try the lower octane stuff in my next tank knowing that it will not hurt the engine...only performance. But thats OK...it is winter and I'm not exactly flying around these Chicago roads!

Without really fixing the problem, you'll be back to that mechanic handing him and Porsche more money on unnecessary repairs next winter.

Your problem is most likely an electrical one that only shows up in cold weather due to material shrinkage or electrical property changes.

It could also be one of any number of engine management sensors that's just slightly off.

These are REALLY hard to track down typically, but until you do, that mechanic is going to keep on mindlessly replacing O2 sensors.