MAF

[nik]

Dear all,

Just a quick note regarding all of those who have suffered MAF problems.

I too had rough running, no power, stuttering revs etc etc. Anyway too cut a long story short, I cleaned the MAF as described in the excellent Renntech tech tips, it certainly made the car run better but still not perfect. took the car to an independant in the UK (Porscheshop) explained the problem to them and told them that I had cleaned the MAF. The mechanic said immediately that too many people change the MAF without first exploring other avenues or possible causes. He had a drive in my car, put it on the ramp and spotted that the breather connector pipe had a huge split in it, part number is 996.107.237.52, cost = £9.86 plus half an hours labour. Car now runs the way it should and I saved the cost of a new MAF.

So I guess if you have changed your MAF and are still experiencing rough running problems then it might be worth just checking the breather pipe for splits before digging deep for O2 sensors.

If this helps even 1 Renntech member then it was worth reporting.

On a different topic (sorry Loren) I purchased some black chrome Cayman 5 spoke wheels, they look absolutey brilliant, I'll post pics tomorrow if anyone is interested.

Regards

Nik

[tommy914]

Where is the "breather pipe"?

Tommy

[csory]

Had a very similar experience - cleaned MAF, cleaned and checked throttle body, took the whole intake apart (looking for air leak), went in about 8 hours of fiddling and digging but no help. Finally disconnected both MAF and the butterfly and the car still responded to throttle - meaning a huge leak behind the throttle body. Yes, it was the breather hose from the oil separator to the intake manifold, had a slit on the bottom side which was closed until the engine vacuum "sucked it open"... :censored:

[Sboxin]

...nik's part number is the 'bellows' connected to the oil separator...

hope this helps someone...probably me in the future <_<

Ed :cheers:

[beety]

Most of the time - before you notice your MAF is failing, the car has been running too rich for such a period that it will inevitably kill the O2 sensors as a knock on effect.

[986Jim]

Most of the time - before you notice your MAF is failing, the car has been running too rich for such a period that it will inevitably kill the O2 sensors as a knock on effect.

Thats acctually a myth... Running too rich or lean will not hurt O2 sensors, contrary to popular belief. I know a lot of people will try and argue me about this, but please call bosch and have them tell you if you need to. Running lean can hurt its time overall beause of extra heat, but generally most O2 sensors are far enough downstream they don't have a problem like this...

O2 sensors read Oxygen only, they don't read fuel or fuel particles, thats why they are called O2 sensors. So as the amount of oxygen changes in the system the sensors read that level and report it back to the ECU. They will survive an enviroment of 0-1600 deg with a long life time. A rich car runs cooler, so it's not hard on the O2 sensor, they don't read fuel, only the particles of air so running rich means there is more unburnt air in the exhaust (along with unburnt fuel) so the O2 sensor will read that info back. Running lean means your Air/Fuel ratio is say 14.7:1 or higher (16:1 lets say) which is the ratio entering the cylinder. If you go rich its the other way around say 10:1. Either way there is sitll combustion happening and the amount of air entering or not entering the exhaust will change and the O2 sensors will read it as per normal. The engine pretty well can't get that far out of the parameters and still run partially normally long enough to really do damage to the sensor.

Normally aspirated cars dont run hot enough (not like turbo) to really do any damage to O2 sensors. My talon has a huge turbo on it and originally had an O2 sensor right behind the turbo in the downpipe. I moved it down the pipe about 10" so it was farther away. I would notice it get lazy when I was running race gas and lots of boost into the 400whp area because the exhaust temps were nearing 1600 deg and the sensor was sooo close to the head. Even that tho didn't kill the sensor, and it ran really rich compared to a N/A car and had way more heat from the exhaust. See where I'm going with this? A 200hp car N/A with the sensor at least 10" away from the head can pretty well do whatever it wants and it's not gonna hurt the sensors..

OK, so here is where I'll stop an wait for some internet expert to jump in and tell me they have seen it 1000 times and I don't know what I'm talking about... <_<

[nik]

Most of the time - before you notice your MAF is failing, the car has been running too rich for such a period that it will inevitably kill the O2 sensors as a knock on effect.

Thats acctually a myth... Running too rich or lean will not hurt O2 sensors, contrary to popular belief. I know a lot of people will try and argue me about this, but please call bosch and have them tell you if you need to. Running lean can hurt its time overall beause of extra heat, but generally most O2 sensors are far enough downstream they don't have a problem like this...

O2 sensors read Oxygen only, they don't read fuel or fuel particles, thats why they are called O2 sensors. So as the amount of oxygen changes in the system the sensors read that level and report it back to the ECU. They will survive an enviroment of 0-1600 deg with a long life time. A rich car runs cooler, so it's not hard on the O2 sensor, they don't read fuel, only the particles of air so running rich means there is more unburnt air in the exhaust (along with unburnt fuel) so the O2 sensor will read that info back. Running lean means your Air/Fuel ratio is say 14.7:1 or higher (16:1 lets say) which is the ratio entering the cylinder. If you go rich its the other way around say 10:1. Either way there is sitll combustion happening and the amount of air entering or not entering the exhaust will change and the O2 sensors will read it as per normal. The engine pretty well can't get that far out of the parameters and still run partially normally long enough to really do damage to the sensor.

Normally aspirated cars dont run hot enough (not like turbo) to really do any damage to O2 sensors. My talon has a huge turbo on it and originally had an O2 sensor right behind the turbo in the downpipe. I moved it down the pipe about 10" so it was farther away. I would notice it get lazy when I was running race gas and lots of boost into the 400whp area because the exhaust temps were nearing 1600 deg and the sensor was sooo close to the head. Even that tho didn't kill the sensor, and it ran really rich compared to a N/A car and had way more heat from the exhaust. See where I'm going with this? A 200hp car N/A with the sensor at least 10" away from the head can pretty well do whatever it wants and it's not gonna hurt the sensors..

OK, so here is where I'll stop an wait for some internet expert to jump in and tell me they have seen it 1000 times and I don't know what I'm talking about... <_<

Interesting point made by Jim, what was surprising was that on the first test drive when the car was running rubbish, sluggish, cutting out early etc the diagnostics reported no faults.

Running badly certainly did affect the MAF (i think) but a quick clean sorted it out, my car runs so much better and has the Boxster howl again.

Slightly off topic (sorry Loren, won't do it again) I drove back the 80 miles or so from the garage at a steady 60, and managed to get 44.6 mpg, I'm now obsessed with trying to get it over 45, I need to get a life I think.!

[Toby]

Normally aspirated cars dont run hot enough (not like turbo) to really do any damage to O2 sensors.

Hi everyone,

I have been reading this forum for a while now, and here is my first post...

A pre-cat O2 sensor failed in my car once, and it was followed by a cat failure. When the dealer exchanged the cat (for free), they told me that the exhaust gas overheated, and "burnt away" the internals of the cat. (I track the car.)

While I am at this...the brand new O2 sensor is throwing the same "aging" code as before... any suggestion on where should I look next?

Thanks!

Toby

Speed Yellow 2001 Boxster S

Edited January 8, 2007 by Toby

[Toby]

Normally aspirated cars dont run hot enough (not like turbo) to really do any damage to O2 sensors.

Hi everyone,

I have been reading this forum for a while now, and here is my first post...

A pre-cat O2 sensor failed in my car once, and it was followed by a cat failure. When the dealer exchange the (for free), they told me that the exhaust gas overheated, and "burnt away" the internals of the cat. (I track the car.)

On the downside...the brand new O2 sensor is throwing the same "aging" code as before... any suggestion on where should I look next?

Thanks!

Toby

Speed Yellow 2001 Boxster S

[Loren]

And the fault code(s) are?

[Toby]

And the fault code(s) are?

Hi Loren,

Here is the history:

1) The original fault codes came on within 1 month after I bought the car back in October 2005. The codes were P0133 and P1275. (aging O2 ahead of cat, cylinder 1-3) I cleared the code a couple times, but each time the CEL came back after a few months. I finally changed the sensor out in August 2006.

2) Within one month (during the next DE) it threw a P1276. (aging O2 ahead of cat, cylinder 4-6) I cleared that code and wait for it to recur, which never did.

3) A week after that, it gave me the cat failure code. (cylinder 1-3, although I don't remember the exact code.) Clear it and it came back immediately. I took the car to the dealer, who replaced the cat under emission warranty.

4) I got another P0133 and P1275 last month. I cleared it and it hasn't recurred (yet.)

The car saw quite a bit of DE action last year, but the fault code appeared before I took the car to the track for the first time.

Thanks for your help!

Toby

Speed Yellow 2001 Boxster S

[Loren]

Well, everything that keeps happening (P0133 and P1275) point to the O2 sensor ahead of the cat.

If your car has 50,000 miles or more chances are that O2 sensor is going, going, gone.

[986Jim]

Normally aspirated cars dont run hot enough (not like turbo) to really do any damage to O2 sensors.

Hi everyone,

I have been reading this forum for a while now, and here is my first post...

A pre-cat O2 sensor failed in my car once, and it was followed by a cat failure. When the dealer exchanged the cat (for free), they told me that the exhaust gas overheated, and "burnt away" the internals of the cat. (I track the car.)

While I am at this...the brand new O2 sensor is throwing the same "aging" code as before... any suggestion on where should I look next?

Thanks!

Toby

Speed Yellow 2001 Boxster S

Racing is a whole different sport. You know the saying. If you ain't breakin parts, you ain't goin fast enough... Good job on blowing them out racing, shows your going for the glory!

If your gonna race it, get a header and straight pipe to your muffler then your O2 sensors will be fine. The cat causes a backup in the exhaust flow, they are 85% of the restriction in your exhaust system. For racing pull them and you will not have problems with the O2 sensors. The cats get so hot and your over whelming them with having the car "on boil" for so long that the O2's then get really hot. It's not the exahust that is ruining them but the cats getting so hot they burnt them out. If you had headers and a straight pipe with no cat it would have never happened.

If your worried about the emissions then get a 200cel cat and add it to the pipe, your computer will be happy too. With a standard straight pipe you will get a CE light for rear O2 sensor not seeing a different reading, catalyst failure or some other stupid code. If you have a cat even 200cel it will give a different reading and not trigger the O2 CE light.

The first 02 sensor is what the ECU looks at for the tune state of the engine. THe rear O2 sensor (after the cat) only measures the catylist efficiency. Basically it should read almost no air particles at all beause the cat would have finished up the combustion process in the cat, so the air/fuel mixture of the exhaust after the cat will be a lot higher as the air is all burnt up. As long as the second 02 can see any different that is within parameter it will be fine. A 200cel cat will do that.

You'll get a lot more flow for racing, no burnt up O2 sensors and still keep the light off...

[Toby]

Thanks!

[tommy914]

If your worried about the emissions then get a 200cel cat and add it to the pipe, your computer will be happy too. With a standard straight pipe you will get a CE light for rear O2 sensor not seeing a different reading, catalyst failure or some other stupid code. If you have a cat even 200cel it will give a different reading and not trigger the O2 CE light.

The first 02 sensor is what the ECU looks at for the tune state of the engine. THe rear O2 sensor (after the cat) only measures the catylist efficiency. Basically it should read almost no air particles at all beause the cat would have finished up the combustion process in the cat, so the air/fuel mixture of the exhaust after the cat will be a lot higher as the air is all burnt up. As long as the second 02 can see any different that is within parameter it will be fine. A 200cel cat will do that.

You'll get a lot more flow for racing, no burnt up O2 sensors and still keep the light off...

Jim,

What is a good source for the cat replacement pipes and the 200cel cat?

thanks

Tommy