MAS.. Airflow Sensor? ok to drive?
12-22-2004, 10:39 PM
#17
Advanced
Join Date: Nov 2003
Location: Mansfield, MA
Posts: 88
Likes: 0
Received 0 Likes
on
0 Posts
Maybe we are stealing Bob's original thread here, but the topic is still Mass Air Flow Sensors and their replacement.
Some good ideas, but they raise more questions. My OBD setup records:
FUELSYS12 (OL, OL; CL, CL) open or closed loop mode for O2 feedback
LOAD_PCT % Calculated Engine Load
ECT F (Engine Coolant Temperature)
SHRTFT1 % Short Term Fuel Trim Bank 1
LONGFT1 % Long Term Fuel Trim Bank 1
SHRTFT2 % Short Term Fuel Trim Bank 2
LONGFT2 % Long Term Fuel Trim Bank 2
RPM rpm
VSS mph (vehicle speed)
SPARKADV deg
IAT F (Inlet Air Temp)
MAF #/min (Mass Air Flow)
TP % (Throttle Position)
AIR ON/OFF secondary air pump
O2SLOC SEE/?
O2S11 SHRTFT11 V,% O2 sensor voltage and associated short term trim
O2S12 V O2 sensor voltage (downstream of the CAT)
O2S21 SHRTFT21 V,% % O2 sensor voltage and associated short term trim
O2S22 V O2 sensor voltage (downstream of the CAT)
Most key variables are measured and recorded in a log file. My previous log files give me some background data, but most is at idle. Only a few short test drives with the laptop connected. Not sure what TRA or FRA parameters are, but I cannot see them with my set up. Aha!!, now that I have written all these parameters out I think my log files contain a ton of data that I never even looked at. I can see the Fuel trim corrections - they are described as "% decrease rich correction" and while the short term numbers vary +/- 6% or so they are on average negative. Long term corrections are virtually identical for both banks (-.78%). I read this as a negative decrease or an increase in the rich correction. It seems like the Motronic must make separate Bank 1 and Bank 2 corrections (learn something every day). While some of the short term corrections do seem larger on one bank, and the average O2 sensor voltages are a bit higher on one Bank, I still suspect the MAFS.
It seems to me that Bosch has been struggling to find a cheap, fast responding, reliable, and accurate flowmeter for electronically fuel injected cars since the early days of L-Jetronic. The current generation MAFS is Hot wire or the similiar Hot film types (I think my C4 has the film type). They use a platinum wire or film that is heated via current, and cooled by flowing air. Platinum is routinely used for temperaure sensors (RTD's or Resistance Temperature Detectors), because it's resistance changes predictibly with temperature and it appears Bosch uses this single platinum wire/film for both the resistance heater and the temperature sensor. They must have calibrated each MAFS design in some type of wind tunnel with known air flows. With no moving parts it should last forever, but I think the slightest dirt film changes the way the air moves over the platinum and as such they fail by reading too low. In other words they under-report the air flow so the ECU under-delivers the fuel and the system runs too lean. The O2 sensors see the lean mixture and the ECU makes a correction. Once the correction exceeds a threshold, the CEL is lit up. I have heard that the oil on the K&N filters can lead to failures of the MAF Sensor. So just what kind of dirt or film could impact the MAFS and how could it be best cleaned? I've only used Porsche paper elements. I cannot find any vacuum leaks, my fuel filter was replaced in the middle of the codes I have, well before the maintenance schedule. The engine seems to run fine. As I am not driving in the Boston salt, I may need to wait a bit before I can collect more data and see if the CEL returns.
Some good ideas, but they raise more questions. My OBD setup records:
FUELSYS12 (OL, OL; CL, CL) open or closed loop mode for O2 feedback
LOAD_PCT % Calculated Engine Load
ECT F (Engine Coolant Temperature)
SHRTFT1 % Short Term Fuel Trim Bank 1
LONGFT1 % Long Term Fuel Trim Bank 1
SHRTFT2 % Short Term Fuel Trim Bank 2
LONGFT2 % Long Term Fuel Trim Bank 2
RPM rpm
VSS mph (vehicle speed)
SPARKADV deg
IAT F (Inlet Air Temp)
MAF #/min (Mass Air Flow)
TP % (Throttle Position)
AIR ON/OFF secondary air pump
O2SLOC SEE/?
O2S11 SHRTFT11 V,% O2 sensor voltage and associated short term trim
O2S12 V O2 sensor voltage (downstream of the CAT)
O2S21 SHRTFT21 V,% % O2 sensor voltage and associated short term trim
O2S22 V O2 sensor voltage (downstream of the CAT)
Most key variables are measured and recorded in a log file. My previous log files give me some background data, but most is at idle. Only a few short test drives with the laptop connected. Not sure what TRA or FRA parameters are, but I cannot see them with my set up. Aha!!, now that I have written all these parameters out I think my log files contain a ton of data that I never even looked at. I can see the Fuel trim corrections - they are described as "% decrease rich correction" and while the short term numbers vary +/- 6% or so they are on average negative. Long term corrections are virtually identical for both banks (-.78%). I read this as a negative decrease or an increase in the rich correction. It seems like the Motronic must make separate Bank 1 and Bank 2 corrections (learn something every day). While some of the short term corrections do seem larger on one bank, and the average O2 sensor voltages are a bit higher on one Bank, I still suspect the MAFS.
It seems to me that Bosch has been struggling to find a cheap, fast responding, reliable, and accurate flowmeter for electronically fuel injected cars since the early days of L-Jetronic. The current generation MAFS is Hot wire or the similiar Hot film types (I think my C4 has the film type). They use a platinum wire or film that is heated via current, and cooled by flowing air. Platinum is routinely used for temperaure sensors (RTD's or Resistance Temperature Detectors), because it's resistance changes predictibly with temperature and it appears Bosch uses this single platinum wire/film for both the resistance heater and the temperature sensor. They must have calibrated each MAFS design in some type of wind tunnel with known air flows. With no moving parts it should last forever, but I think the slightest dirt film changes the way the air moves over the platinum and as such they fail by reading too low. In other words they under-report the air flow so the ECU under-delivers the fuel and the system runs too lean. The O2 sensors see the lean mixture and the ECU makes a correction. Once the correction exceeds a threshold, the CEL is lit up. I have heard that the oil on the K&N filters can lead to failures of the MAF Sensor. So just what kind of dirt or film could impact the MAFS and how could it be best cleaned? I've only used Porsche paper elements. I cannot find any vacuum leaks, my fuel filter was replaced in the middle of the codes I have, well before the maintenance schedule. The engine seems to run fine. As I am not driving in the Boston salt, I may need to wait a bit before I can collect more data and see if the CEL returns.
12-23-2004, 12:02 AM
#18
Race Car
Your are correct that the STFT will change rapidly as the engine runs, making quick changes in the amount of fuel being delivered. The LTFT is a learned percentage of what corrections have had to be made by the STFT. If the number is positive, it means that the computer is, on average, having to add that prcentage of fuel to the engine. Negative LTFT means it has had to reduce that amount of fuel.
One thing that you might look at is the secondary (after cat) O2 sensor readings. You need to look at what the reading is at WOT. It both sensors should report .85 volts or higher. If they do not, it woul be an indication that you are running lean.
Your fuel trim looks fine, so it appears that the MAF is properly reading the amount of air that is passing by it.
You state that your car runs properly, so are you getting a CEL? And if so,what is the error code reported? It is a good idea to keep some of the old logs from the scanner. It gives you something to compare to when you do have problems.
One thing that you might look at is the secondary (after cat) O2 sensor readings. You need to look at what the reading is at WOT. It both sensors should report .85 volts or higher. If they do not, it woul be an indication that you are running lean.
Your fuel trim looks fine, so it appears that the MAF is properly reading the amount of air that is passing by it.
You state that your car runs properly, so are you getting a CEL? And if so,what is the error code reported? It is a good idea to keep some of the old logs from the scanner. It gives you something to compare to when you do have problems.
12-23-2004, 01:18 AM
#19
"Not sure what TRA or FRA parameters are,"
They are the long & short adaptation variables you're getting on your scanner.
Bottomline:
1. both banks should indicate zero short/long term corrections
2. both front O2 sensors should vary over the voltage
range and must respond within a time limit, i.e. they must
have minimum frequency (Fsensed - O2 sensor > Fmin)
3. the rear sensors must be stable
Note:
You can determine fuel injection problems by monitoring the readiness states,
i.e. incomplete states indicate potential problems.
They are the long & short adaptation variables you're getting on your scanner.
Bottomline:
1. both banks should indicate zero short/long term corrections
2. both front O2 sensors should vary over the voltage
range and must respond within a time limit, i.e. they must
have minimum frequency (Fsensed - O2 sensor > Fmin)
3. the rear sensors must be stable
Note:
You can determine fuel injection problems by monitoring the readiness states,
i.e. incomplete states indicate potential problems.
12-23-2004, 09:53 AM
#20
Race Car
Loren:
I have to disagree with you on the LTFT. They do not need to be, nor are they rarely close to zero. My current setup runs about - 12%. Stock was a little positive on both banks. My Toyota runs about +11; BMW about -5; Honda +6 and Nissan +9.
I have yet to see a car with LTFT at ZERO. I am sure they are out there, but chances of getting a perfect match of an injector size would be very difficult, stock or otherwise.
Also, everyone should be reminded that the after cat O2 sensor MUST Jump to a high voltage immediately at WOT. A safe rule of thumb is a,85 volts or higher. Less than this is an indication of a lean condition. This is the primamry reading you need to take after any type of tuning of the fuel system.
I have to disagree with you on the LTFT. They do not need to be, nor are they rarely close to zero. My current setup runs about - 12%. Stock was a little positive on both banks. My Toyota runs about +11; BMW about -5; Honda +6 and Nissan +9.
I have yet to see a car with LTFT at ZERO. I am sure they are out there, but chances of getting a perfect match of an injector size would be very difficult, stock or otherwise.
Also, everyone should be reminded that the after cat O2 sensor MUST Jump to a high voltage immediately at WOT. A safe rule of thumb is a,85 volts or higher. Less than this is an indication of a lean condition. This is the primamry reading you need to take after any type of tuning of the fuel system.
12-23-2004, 11:26 AM
#21
Hey, out of curiosity what obdII interface and software are you using? I had a setup once, ISO type that worked but would make my laptop crash so I returned it! Thanks, btw cheaper is always better as long as it gives the same info etc.
12-23-2004, 12:50 PM
#22
Advanced
Join Date: Nov 2003
Location: Mansfield, MA
Posts: 88
Likes: 0
Received 0 Likes
on
0 Posts
It's very helpful to see the know-how and data collected by others, so that one might interpret the data from their own engine and learn to maintain it without replacing perfectly good parts via trial and $error$. My understanding is that any long term corrections (or short term corrections for that matter) are an indication that the MAF based calculation of the fuel amount has errors. If you look at all the other variables the ECU uses to compute the fuel amount (ECU computes the fuel amount as the duration the injectors stay open), you would suspect the MAFS to be the major source of error. i.e. a 2% error in the MAF with all other variables perfect would give a 2% long term correction in fuel amount after the O2 feedback correction. A 2% error in manifold pressure, manifold temperature, rpm etc... would be much less adjustment to the long term correction. To meet the compromise of emissions (run lean), fuel economy (run close to stoichiometric A/F ratio), and power (run rich) the ECU has a 3-D MAP, so that MAF is not exactly proportional to the fuel, but still quite close. The ECU interprets WOT (I hope so) as a request for power, thus operation on the rich side, thus 0.8 volts or higher on the O2 sensors, a good test to show the O2 sensors are responsive. Not sure where Bosch leaves off and Porsche picks up when they program the ECU for a particular engine. I want the MAP for my car. Where is it?
I played back a few more log files. I did see some large short term corrections +/- 20% just after starting the engine. I also saw some long term corrections of up to -8%. But based on previous posts I now think I need to collect data on a longer drive, under normal conditions and also to get the O2 data for WOT.
So why is all of this technical stuff so important?
In Massachusetts we now have new vehicle emissions testing (June 1, 2004):
http://www.mass.gov/dep/pao/news/imfinal6.htm
To coincide with the program improvements announced today, Massachusetts will introduce pass/fail On-Board Diagnostics (OBD) emissions testing for all model year 1996 and newer cars and SUVs, and most light trucks this summer. The new test relies on data from the internal computer that continuously monitors a vehicle’s engine, transmission, and emissions control system.
As soon as OBD pass/fail testing begins, tailpipe testing will no longer be needed for more than 60 percent of the cars, light trucks and SUVs in Massachusetts. Within four years, less than 10 percent of the state’s motor vehicle fleet is expected to need tailpipe testing.
Now about saving money and keeping the engine running perfectly:
Can I effectively clean the MAFS with "electrical dust remover"? Like radio shack tetrafluoroethane in a can? Can I wipe the platinum film with a cloth or brush? Blow it out with compressed air?
Yes this is fun!!
Why?
Because Porsche, Mercedes, BMW... would love to have you at their mercy for service. I've heard that Volvo only allows the dealer to connect to a central Volvo computer for diagnostics. Yuk. With a $120 OBD link and the know-how to use it, the user community might come up with some clever ideas keep our engines purring or even making some improvements. I guess it's about having some control over your own destiny and the satisfaction of successfully maintaining such a complex piece of machinery.
Where the heck can you get a good manual for DME 5.2.2 or maybe my C4 is actually DME 7.2?? Is there a label on the ECU? There is no DME version on the engine lid.
SPR
I use this OBD setup:
http://www.obd-2.com/
I played back a few more log files. I did see some large short term corrections +/- 20% just after starting the engine. I also saw some long term corrections of up to -8%. But based on previous posts I now think I need to collect data on a longer drive, under normal conditions and also to get the O2 data for WOT.
So why is all of this technical stuff so important?
In Massachusetts we now have new vehicle emissions testing (June 1, 2004):
http://www.mass.gov/dep/pao/news/imfinal6.htm
To coincide with the program improvements announced today, Massachusetts will introduce pass/fail On-Board Diagnostics (OBD) emissions testing for all model year 1996 and newer cars and SUVs, and most light trucks this summer. The new test relies on data from the internal computer that continuously monitors a vehicle’s engine, transmission, and emissions control system.
As soon as OBD pass/fail testing begins, tailpipe testing will no longer be needed for more than 60 percent of the cars, light trucks and SUVs in Massachusetts. Within four years, less than 10 percent of the state’s motor vehicle fleet is expected to need tailpipe testing.
Now about saving money and keeping the engine running perfectly:
Can I effectively clean the MAFS with "electrical dust remover"? Like radio shack tetrafluoroethane in a can? Can I wipe the platinum film with a cloth or brush? Blow it out with compressed air?
Yes this is fun!!
Why?
Because Porsche, Mercedes, BMW... would love to have you at their mercy for service. I've heard that Volvo only allows the dealer to connect to a central Volvo computer for diagnostics. Yuk. With a $120 OBD link and the know-how to use it, the user community might come up with some clever ideas keep our engines purring or even making some improvements. I guess it's about having some control over your own destiny and the satisfaction of successfully maintaining such a complex piece of machinery.
Where the heck can you get a good manual for DME 5.2.2 or maybe my C4 is actually DME 7.2?? Is there a label on the ECU? There is no DME version on the engine lid.
SPR
I use this OBD setup:
http://www.obd-2.com/
12-23-2004, 01:00 PM
#23
"As soon as OBD pass/fail testing begins, tailpipe testing will no longer be needed for more than 60 percent of the cars, light trucks and SUVs in Massachusetts. Within four years, less than 10 percent of the state’s motor vehicle fleet is expected to need tailpipe testing."
The key now for emissions testing is the use of OBDII data and the readiness codes which
provide an indication of the state of the emission system.
Here's some info from my web site:
Common Generic OBDII Fault Codes (DTC)
X1XX, X2XX - Fuel & Air Systems
X3XX - Ignition System
X4XX - Emission System
X5XX - Auxilary Functions
X6XX - Engine Control Module Functions
X7XX - Transmission Interface Functions
1XXX - OEM Proprietary
XXXZ - Same type of fault, Z - specific fault location/value
0100 - Mass Air Flow Sensor (MAFS)
0105 - Manifold Abosolute Pressure (MAP)
0110 - Intake Air Temperature (IAT)
0115 - Engine Coolant Temperature (ECT)
0120 - Throttle Position Sensor (TPS)
0130 - O2 Sensor, Bank 1 - Front Sensor
0140 - O2 Sensor, Bank 1 - Rear Sensor
0150 - O2 Sensor, Bank 2 - Front Sensor
0160 - O2 Sensor, Bank 2 - Rear Sensor
0200 - Injector Circuit
0230 - Fuel Pump Circuit
0300 - Random Cylinder Misfire
0330 - Knock Sensor (KS)
0335 - Crankshaft Position Sensor (CKP)
0340 - Camshaft Position Sensor (CMP)
0400 - Exhaust Gas Recirculation (EGR)
0410 - Secondary Air Injection (SAI)
0420 - Catalytic Converter Efficiency, Bank 1 (TWC)
0430 - Catalytic Converter Efficiency, Bank 2 (TWC)
0440 - Evaporative Emission Control System (EVAP)
0500 - Vehicle Speed Sensor (VSS)
0560 - System Battery Voltage
0605 - General Control Circuit (ECM)
0650 - Malfunction Indicator Lamp (MIL)
1. OBDII DTCs are accessed via the diagnostic link connector (DLC),
located in the passenger compartment near the steering column.
2. OBDII DTCs are not cleared by ECM/battery removal.
3. Most OBDII scanners provide a description of the generic DTCs,
in addition to the numeric code, but not for the proprietary DTCs.
4. Some OBDII DTCs do not set the MIL but are stored.
Basic OBDII Readiness Codes
Non-Continuous Tests
- Three Way Catalytic Converter (TWC) Effeciency
- Fuel Tank Ventilation (EVAP)
- Secondary Air Injection (SAI)
- Oxygen Sensors
- Oxygen Sensor Heating
Continuous Tests
- Fuel System (TRIM)
- ECM Faults (DTC)
- Cylinder Misfire
1. Monitored & Set During Three Cycles; Warm-up, Driving, & Trip
Warm-up Cycle - SAI, EVAP, (from cold start to operating temperature, 2 min. minimum)
Driving Cycle - O2 Sensors/Heating, TWC, TRIM, (2 min. idle, 5 min. drive, 2 min. idle)
Trip Cycle - Diagnosis of All ECM Systems, (2nd Driving Cycle after shut-down, 20 min. max.).
2. Completed Prior to an Emissions Test.
3. Accessed via the OBDII Connector (DLC).
4. Reset by a DTC clear or a battery disconnection.
5. Some non-continuous tests can be run ("short test") via special scanners.
"I have to disagree with you on the LTFT. "
You need to buy the Porsche OBDII manual (WKD 483 320) and read
beginning on page F-15.
The key now for emissions testing is the use of OBDII data and the readiness codes which
provide an indication of the state of the emission system.
Here's some info from my web site:
Common Generic OBDII Fault Codes (DTC)
X1XX, X2XX - Fuel & Air Systems
X3XX - Ignition System
X4XX - Emission System
X5XX - Auxilary Functions
X6XX - Engine Control Module Functions
X7XX - Transmission Interface Functions
1XXX - OEM Proprietary
XXXZ - Same type of fault, Z - specific fault location/value
0100 - Mass Air Flow Sensor (MAFS)
0105 - Manifold Abosolute Pressure (MAP)
0110 - Intake Air Temperature (IAT)
0115 - Engine Coolant Temperature (ECT)
0120 - Throttle Position Sensor (TPS)
0130 - O2 Sensor, Bank 1 - Front Sensor
0140 - O2 Sensor, Bank 1 - Rear Sensor
0150 - O2 Sensor, Bank 2 - Front Sensor
0160 - O2 Sensor, Bank 2 - Rear Sensor
0200 - Injector Circuit
0230 - Fuel Pump Circuit
0300 - Random Cylinder Misfire
0330 - Knock Sensor (KS)
0335 - Crankshaft Position Sensor (CKP)
0340 - Camshaft Position Sensor (CMP)
0400 - Exhaust Gas Recirculation (EGR)
0410 - Secondary Air Injection (SAI)
0420 - Catalytic Converter Efficiency, Bank 1 (TWC)
0430 - Catalytic Converter Efficiency, Bank 2 (TWC)
0440 - Evaporative Emission Control System (EVAP)
0500 - Vehicle Speed Sensor (VSS)
0560 - System Battery Voltage
0605 - General Control Circuit (ECM)
0650 - Malfunction Indicator Lamp (MIL)
1. OBDII DTCs are accessed via the diagnostic link connector (DLC),
located in the passenger compartment near the steering column.
2. OBDII DTCs are not cleared by ECM/battery removal.
3. Most OBDII scanners provide a description of the generic DTCs,
in addition to the numeric code, but not for the proprietary DTCs.
4. Some OBDII DTCs do not set the MIL but are stored.
Basic OBDII Readiness Codes
Non-Continuous Tests
- Three Way Catalytic Converter (TWC) Effeciency
- Fuel Tank Ventilation (EVAP)
- Secondary Air Injection (SAI)
- Oxygen Sensors
- Oxygen Sensor Heating
Continuous Tests
- Fuel System (TRIM)
- ECM Faults (DTC)
- Cylinder Misfire
1. Monitored & Set During Three Cycles; Warm-up, Driving, & Trip
Warm-up Cycle - SAI, EVAP, (from cold start to operating temperature, 2 min. minimum)
Driving Cycle - O2 Sensors/Heating, TWC, TRIM, (2 min. idle, 5 min. drive, 2 min. idle)
Trip Cycle - Diagnosis of All ECM Systems, (2nd Driving Cycle after shut-down, 20 min. max.).
2. Completed Prior to an Emissions Test.
3. Accessed via the OBDII Connector (DLC).
4. Reset by a DTC clear or a battery disconnection.
5. Some non-continuous tests can be run ("short test") via special scanners.
"I have to disagree with you on the LTFT. "
You need to buy the Porsche OBDII manual (WKD 483 320) and read
beginning on page F-15.
12-23-2004, 02:57 PM
#24
Race Car
More than a bad MAF will effect the STFT and LTFT. As the air filter gets dirty, the LTFT will grow negative. Put in a new filter and it will go more positive. As the injectors get dirty, LTFT will get more negative. Change in fuel quality or fuel pressure will effect it. The temperature of the air going into the intake will effect it.
This is an ever learning variable that will adjust to many driving conditions. Keep this in mind when comparing current readings to past ones.
This is an ever learning variable that will adjust to many driving conditions. Keep this in mind when comparing current readings to past ones.
