autobonrun

I've searched the 993 board and can find little if any discussions on the MAF sensor. On one of the M5 boards, there is considerable discussion, and a general concensus that the signals from the sensors degrade over time. So, many replace their sensors after 60k or so miles. The fuel flow rate is available on the cars' computers and some measurements taken show that inaccurate MAF's can cause a fuel flow that's 10-20% less than that with new MAF sensors. This means of course that the power produced is also reduced.

Does anyone here consider the Porsche MAF a maintenance item that should be replaced after some amount of mileage or time? Is the air or fuel flow rate available over the OBD I or II port? Lastly, has anyone here replaced their sensors due to signal degredation rather than an absolute failure and did you see any difference in your car's performance?

flatsixforme

As a side note, if you put your MAF in backwards it makes the car have a wicked idle and smell rather rich...found this out last weekend with some buddies replacing our SAI Valves (horray...it's done!).

Steve Weiner-Rennsport Systems

Hi:

I don't consider a MAF a regular replacement item unless its failed or been contaminated.

I do clean them with a special solvent made specifically for MAF's (CRC) and I clean the throttle assembly every 50K for best idle & performance. The latter item gets coated with oil from the oil tank breather over time and that affects idle and off-idle therottle response. Carb cleaner works best for that application.

autobonrun

I've used some of the CRC stuff and plan to do the one on my 993 as well. Sounds though like you've not heard of any sensor outputs degrading over time?

WarpMan

Steve,
Is the throttle assembly easy to get to and what would be the best way to go about the cleaning?

Mark Harris

Steve Weiner-Rennsport Systems

It takes some patience to access since its in front of the intake system.

I just remove the airbox, then the MAFS to gain access to the throttle assembly. Some folks clean it on the engine and some prefer to remove it and clean it on the bench (my preference) to avoid any contamination of the oxysensor from the carb cleaner and carbon deposits being flushed into the intake manifold.

Depending how adept you are, you can use a mirror and a light to look at the throttle while you spray carb cleaner at the blade and around the circumference. Its tougher to clean the air bypass passages that feed the ISV while on the engine so thats why I like to remove it.

Jenner

autobonrun, as you can see from my signature I'm a fellow 2003 M5 owner and know the exact discussions you mention from M5board.com

While I don't have enough time with my 993 Turbo to give any input on the subject, I can tell you that the previous owner had the MAF replaced during a service at 47,691 miles. The reasoning on the invoice states:
"Found that Mass Air Flow Sensor is not reading properly and needs to be replaced. Replaced Mass Air Flow Meter and retest. Vehicle running good at this time." The cost shown for the MAF Sensor is $431.51

At least there aren't two like in the M5!

Not sure if this helps at all but I figured I'd post it up just in case.

Stealth 993

My thought is if it's not throwing a code, leave it alone.

Lots of other cars have MAF problems, & a lot are from over oiling K&N type air filters. On my Audi S4, I keep a spare MAF, they are a known failure point. Usually once a year when I do all the fluid flushes, I will clean out the MAF's with some CRC, it's easy, & cheap maintaince.

vee12

If you over the oil level and it "backs up" and contaminates the MAF it will need cleaning/replacementr also. According to several shops this a fairly regular occurence for many 993 and Boxster owners.

autobonrun

This is helpful information. You're right. At least we only have one MAF in the 993, not two. It would be nice to know what test the dealer ran to determine it was not reading properly. Anyone with OBD software ever looked for fuel flow in the Porsche's computer?

It's interesting that there is so little discussion of the MAF with one manufacturer and so much discussion with another manufacturer, about the same technology. That's what got me thinking that my 993 may not be producing optimum power if the MAF is the original one.

Stealth, I hear what you're saying. The discussion on the other board centers around the consensus opinion that the sensor's accuracy and output signal degrades over time and will impact the car's performance long before it ever fails completely or before it gets bad enough to trip a code.

Many M5 owners who were not achieving full fuel flow rate under full throttle saw the fuel flow and also power increase after the MAFs were replaced.

If anyone is interested in the tech discussion, it's in the attached link.

http://www.m5board.com/vbulletin/showthread.php?t=54788

geolab

I just changed mine for no reason. 100k km.
PST2 monitors air temp, press. , and quantity etc...
The old and new gave practically same measures
Sent old to bosch to check, returned checked with no charge (MAF still great, they didn't do anything on it)

BUT....

Car since birth has had original air filters changed very frequently. And between intervals, filter was air pressure cleaned. Original airbox...
THUS, no reason to take intake out to clean, which I did.
Intake was shining silver inside outside

Someone mentioned oil overfill... oil does not get to MAF.
.
.
.

Jenner

FYI it wasn't a dealer it was an indy. I can ask if they remember what the codes/symptoms were but it was back in May 2007.

Stealth 993

On the 993, can we hook up to the ODBII & read the MAF flow rates? On my Audi, I have cool software that lets me log any sensor on the car & graph it. I can read the RPM, MAF & O2's & see if everything is fine.

There are also some simple ohm meter test you can do to the MAF, just not sure what the values should be on the 993, & you can also hook it up to an oscilloscope.

1pcarnut

[QUOTE=Stealth 993;4995007]On the 993, can we hook up to the ODBII & read the MAF flow rates? On my Audi, I have cool software that lets me log any sensor on the car & graph it. I can read the RPM, MAF & O2's & see if everything is fine.


Very interested in the anwer to this question regarding OBD scanners since I'm looking for a hand held one at the moment.