So, after cleaning my MAF in the "DIY: MAF cleaning", (09-30-2005) my car was running like a champ. However, it appears to have gotten dirty/is failing yet again (01-07-2005).

I recently got the same CEL code, P0175 (system too rich bank 2). I immediately hooked up my datalogger and looked at my short term fuel trims (STFT) while at idle (which is when you should check your STFTs if you suspect the MAF).

To my surprise, BOTH of my banks (1&2) were reading at about -18 to -22% trim while at idle. It was only a matter of time before Bank 1 threw a code as well (P0172). It is VERY important to know that BOTH banks were acting the same way. If it had been one bank, then I would have had to look at an O2 sensor and/or leaking injector as my first problem area.

A summary on the subject and the symptoms that I was getting (datalogger verified):

When a MAF sensor gets contaminated, it skews the transfer function such that the sensor over-estimates air flow at idle (causes the fuel system to go rich) and under-estimates air flow at high air flows (causes fuel system to go lean). This means Long Term Fuel Trims will learn lean (negative) corrections at idle and learn rich (positive) corrections at higher air flows. Short term fuel trims will run even more lean (negative) at idle as well as they are the quick-acting fuel trims so to speak.

You can look at the previous threads on the subject:

https://www.6speedonline.com/forums/...threadid=30697
https://www.6speedonline.com/forums/...threadid=30929
https://www.6speedonline.com/forums/...threadid=33062

Given the benefits that the cleaning did, I have narrowed down my CEL's and low-speed hesitation to the MAF. It either got dirty again or is in the process of failing. I pulled my MAF with the intention of cleaning it yet again. I then decided to try and start my car w/o the MAF installed/hooked up to satifsy my own curiousity...

To my surprise, my STFTs read at -20 to -22%, the SAME that it was reading WITH the MAF hooked up. Basically, my MAF wasn't providing for any correction and my fuel trims were having to compensate. Also, I immediately got the ABS/PSM error dash lights as well. Almost everyone with the Upsolute chip has probably seen the ABS/PSM lights come on during hard acceleration. I am not sure if other chips give the same symptoms as well.

What I have concluded:
- I probably need a new MAF (I have 33k+ on the car with the stock air filter). No amount of cleaning is going to bring my MAF back to life if it is failing.
- Get a datalogger! It will help you diagnose problems and save you a ton of $$$ from the dealer when you can easily replace your own MAF (if need be) or read out the error codes.
- If BOTH of your STFTs are sitting in the high negatives at idle (-15 or -20% correction factor) and you throw a P0175 and/or P0172 CEL, then you probably have a failing or contaminated MAF. Your first step should be to try and clean it. If that doesn't help, then the next step will probably be to replace the MAF.

*NOTE* - On looking for MAF pricing, I have come across this:
Bosch
Air Mass Sensor
For models with M620 e-accelerator, for original 99660612400 or updated 98660612501 Porsche units. Please verify part number on existing unit prior to ordering. 1 per car.

I have an '01 with part # 99660612400 in my car. Oddly enough, there appears to be an updated version? 99660612501 is mentioned as well. Can anyone explain this to me? Stephen? Can someone with a newer 996TT take a look at their MAF and find out the part # on it? I would be curious to know if Porsche was aware that there could be MAF issues on earlier 996TTs and thus, developed an updated version.

Either way, I hope that this is of help to the TT owners on this site.

-ruiner

 

Heya buddy..

one is actually a boxster MAF (the cheaper one) and the other is the regular 996 one. The 986 one DOES actually work with our cars but you need to get an "update" from the dealer for it to idle correctly. Porsche started using the 986 MAF on all 996TT's from 04 onwards just to show us all how crap the old 996TT MAF really was...

 

Alex, I knew that the Boxster one was supposed to be cheaper, but I have the cheaper one, apparently.

Here:

http://www.autohausaz.com/search/pro...0Mass%20Sensor

As can be seen, I have the "cheaper" version, 99660612400, by default. If you search specifically for the 996TT, you will get the $210 one as well. What is the more expensive one? What car does that go on? Perhaps an earlier boxster? Maybe Porsche revised the unit? I have an '01, so the '04 change wouldn't affect me (unless the dealership slipped one in w/o me knowing).

 

Thanks for the info, Ruiner. If I may ask...which datalogger do you recommend and where can I purchase one? TIA.

 

Maybe we need a group buy and get a better price. I am definately getting a spare.

I cleaned my MAF last weekend and it seemed to help but I think its definately on it's last leg.

 

Well, since I had a spare Palm Pilot laying around, I bought the Pocketlogger. Even if you don't have one, you can pick up a cheap one for $10-50 on Ebay. I think that the Pocketlogger kit runs $125 for the ODBII cable and software. I believe that Zippy also runs it and so does Lizard1. Here is a short thread or two on it:
https://www.6speedonline.com/forums/...threadid=26998
https://www.6speedonline.com/forums/...threadid=29830

PDA compatibily list for the Pocketlogger:
http://www.pocketlogger.com/index.php?pid=faq_pda_list


*NOTE* - For those that do order the Pocketlogger, ask for (order) version 2.0. It is still in beta, but very stable. I have been using it for over 1 year and had no problems with it. There are more features and you will get better benefit from the software. Read about it here: http://www.pocketlogger.com/forum/viewtopic.php?t=344

More info on the Pocketlogger for ODBII cars:
http://www.pocketlogger.com/index.php?pid=obdii
http://www.pocketlogger.com/index.php?pid=plobdii

This will also read and clear the CEL codes. It's nice to watch the CEL light disappear from your dash when you clear the error code after reading it.

It will also read a list of parameters that will allow you to log/tune your car:
http://www.pocketlogger.com/index.ph...ams&type=obdii

OBDII Parameters at about 15-18 samples per second:

Calculated Load
Coolant Temperature
Short Term Fuel Trim Bank X
Long Term Fuel Trim Bank X
Fuel Pressure (Gauge)
Intake Manifold Absolute Pressure
Engine RPM
Vehicle Speed
Ignition Timing Advance
Intake Air Temperature
Air Flow Rate from MAF
Throttle Position
Oxygen Sensor Bank X Sensor Y


If you get a CEL light for an o2 sensor, you can log your problem o2 sensor and see why it is throwing the code. If you are getting knock, you can log the Ignition Timing Advance, Load, and RPM to see if the timing is being pulled at a particular RPM while wide open throttle.

Let me know if you have any questions. This unit will also work on most other vehicles that are 1996 and above. I use it on my Land Rover, my mother's Mercedes, my friend's japanese cars, etc.

A few screenshots:

 

A dirty MAF wire will cause your engine to be more LEAN and NOT rich. The hot wire reports air volume to the computer based on the current generated by the MAF sensor. The MAF maintains the hot wire at a specific temperature and as air passes over it, it must increase current to the wire in order to maintain this temperature. This current level is reported to the computer that adjusts fuel accordingly. The greater the current, the greater the amount of air the computer thinks is entering the engine.

If your MAF is dirty, the air passing over the wire does not cool the wire as much as it would if it was clean. Therefore, the current to the wire, and subsequently sent to the comuter, does not have to be as great to maintain the temperature of the wire. In this case, the MAF is reporting less air to the computer than is actually entering the engine and the computer will inject less fuel than is actually needed. LEAN condition developes.

As for why your STFT showed such high negative adjsutments, I have no idea unless you engine was not fully warmed up, but it was definately not because the MAF was dirty. If your MAF was blown, the system would default to a rich setting and you would see negative adjustment to your LTFT.

What was the reading of your MAF at idle?

 

i put a boxter maf in about 6 month ago
and did not go to the dealer to flash the ecu


my idle is just like before but the car runs a lot better
smoother.

hope it helps


Boris

 

Remember, there are only 2 ways to BLOW a MAF. You either have to damage it physically (break wire(s)) or run too much current through it. If you increase air flow too much and do not control the current going to the MAF (such as through resisters), you will blow the sensor in a few months. Take a look at the MAF reading at WOT and full redline and see what type of airflow reading you are getting. You MUST maintain the maximum voltage within the specs of the MAF or you will continue to have to replace them every few months.

 

I am aware of how a hot-wire MAF works, but there has to be another correction factor (such as a temp sensor ) that is not being accounted for. I cannot read my MAF's voltage output with my datalogger, but I can read the airflow. I need to log that again. I can, however, read my fuel trims.

My MAF is not blown, either, but perhaps it is almost dead. I think that it is on its way out. This would also explain why I would trip the code on a humid/wet day. Remember, I am affecting both banks. I was getting *almost* the same STFT values with the MAF unplugged as I did with it in. However, those values went back to normal only after I cleaned my MAF (they would cycle +/- 5 while at idle). However, in the condition that it is before I cleaned it and now, I am constantly sitting at ~ negative 20ish at idle. My LTFTs are also running positive under high/WOT throttle. I don't believe that I have a leak in the system, either.

My car was more than warmed up at all times that I have datalogged my car. This wasn't the first time that I have seen this pattern. The only thing that changed this pattern was cleaning the MAF...

 

At WOT, your fuel trims should be going to ZERO. During this time, the only sensor the computer is looking at for fuel control is the MAF. What the O2 sensors see is ignored.

 

What does your datalogger say your max air flow is? What is the upper limit of the stock MAF?

 

Yes, closed vs open loop tables. Unfortunately, I do not know the algorithm used to determine open loop settings (RPM level, throttle position, etc). Some cars go open loop after a certain RPM even if the throttle isn't above a certain position. I just dunno...

 

I would need to log that. Unfortunately, my MAF is out of the car right now. I might put it back in and do some runs in high gears so that I get max airflow intake via engine load.

 

Below I have taken two points in the same datalog. You can see the STFT (bank 1 and bank 2), Airflow (lbs/min), and RPM. I barely cleaned the MAF before I put it back in, so I was not getting the typical -22 or so at idle that is enough to throw a CEL. I was getting -20 to -23 Thursday night before I pulled my MAF (measured after the car was warmed up). However, -13 to -15 is just as bad in my opinion.

When I really cleaned my MAF back in Sept, I was getting around -5 to +5 at idle for my STFTs. Now, they are sitting at full negative values at idle (when both cold and warmed up).

Click on the thumbnails...

Log @ 4920rpm with WOT:


Log @ 768rpm (idle)