So we have questions from customers from time to time on how to acutally utilize their fancy OBD2 diagnostics. Ill keep this thread updated but its currently just thrown together off the top of my head.
For this you have a few different options.
The most simple/common is to get a 20pin adapter for the obd2 port:
Cheapest here
From there you will need something to feed you data. If you want the most simple setup you should look into a simple OBD2 wifi dongle (or Bluetooth for you android guys)
Found here
From there you can get the torque app, or something like OBD2 fusion.
Another alternative is to get a OBD2->USB cable like this one:
found here
Which will enable you to hook your car upto a laptop and utilizie software like INPA, testo (found here) or Romraider/logger
Once youre able to grab all this data what does it mean and what can you do with it!?!
First and formost is the most common cause of CELs is vac leaks. These spit codes for fuel trims and whatnot. Using your fancy new tools you can get some feedback on what is really going on.
(Pcode list for those using OBD2 scanners)
OBD2 Speak:
STFT: This is instantaneous fuel trim and will bounce around while idling and driving.
LTFT: This is learned long term adaption based off a rolling average of sorts for STFT.
BMW Speak:
Lambda Integrator: Same as STFT
Additive Trim: This is long term learned STFT for IDLE conditions
Multiplicative Trim: This is long term learned STFT for Cruise Conditions
To put it simply the bmw additive and multiplicative are added together to output OBD2 LTFT data.
Now that i understand that, why the hell is my CEL coming on?
Basically fuel trims add (+) or remove (-) fuel to the base fuel map based off O2 sensor feedback. The MAF sees a certian amount of air coming in, grabs a position on the fuel table based off that airflow and RPM and injects a specific amount of fuel. The O2 sensors then watch to make sure that amount of fuel injected matches the target AFR (which is usually 14.7 or stoic). For 100 different reasons its not always perfectly precise, so the fuel trims add or take away from the base fuel table to try to achieve the target AFR.
When you have a vacuum leak youve now really confused the system. Unmetered air that the ECU is unaware of is now entering the engine. Its burned and passes to the O2 sensors which now see all this extra air and assume that the base fuel map needs adjusting and begin to trim that section of the fuel table (again RPM vs airflow). It will begin adding fuel to compensate for the extra air its seeing even though technically it doesnt really need the extra fuel. This causes rough running and horrible MPG as the ECU is pouring fuel unaware that an otherwise *normal* amount of air is entering the engine, its just missing the MAF.
Other possible issues that the ECU will try to 'fix' are, wrong sized injectors for the tune, low/bad fuel pressure, clogged injectors, etc. These situations can cause both + and - Fuel trims..
From there going further into diagnosing the 'health' of your setup you can get into data logging. Which basically grabs a number of data points from various sensors and plots them for you to analyze. Will go into further detail on this:
For this you have a few different options.
The most simple/common is to get a 20pin adapter for the obd2 port:
Cheapest here
From there you will need something to feed you data. If you want the most simple setup you should look into a simple OBD2 wifi dongle (or Bluetooth for you android guys)
Found here
From there you can get the torque app, or something like OBD2 fusion.
Another alternative is to get a OBD2->USB cable like this one:
found here
Which will enable you to hook your car upto a laptop and utilizie software like INPA, testo (found here) or Romraider/logger
Once youre able to grab all this data what does it mean and what can you do with it!?!
First and formost is the most common cause of CELs is vac leaks. These spit codes for fuel trims and whatnot. Using your fancy new tools you can get some feedback on what is really going on.
(Pcode list for those using OBD2 scanners)
OBD2 Speak:
STFT: This is instantaneous fuel trim and will bounce around while idling and driving.
LTFT: This is learned long term adaption based off a rolling average of sorts for STFT.
BMW Speak:
Lambda Integrator: Same as STFT
Additive Trim: This is long term learned STFT for IDLE conditions
Multiplicative Trim: This is long term learned STFT for Cruise Conditions
To put it simply the bmw additive and multiplicative are added together to output OBD2 LTFT data.
Now that i understand that, why the hell is my CEL coming on?
Basically fuel trims add (+) or remove (-) fuel to the base fuel map based off O2 sensor feedback. The MAF sees a certian amount of air coming in, grabs a position on the fuel table based off that airflow and RPM and injects a specific amount of fuel. The O2 sensors then watch to make sure that amount of fuel injected matches the target AFR (which is usually 14.7 or stoic). For 100 different reasons its not always perfectly precise, so the fuel trims add or take away from the base fuel table to try to achieve the target AFR.
When you have a vacuum leak youve now really confused the system. Unmetered air that the ECU is unaware of is now entering the engine. Its burned and passes to the O2 sensors which now see all this extra air and assume that the base fuel map needs adjusting and begin to trim that section of the fuel table (again RPM vs airflow). It will begin adding fuel to compensate for the extra air its seeing even though technically it doesnt really need the extra fuel. This causes rough running and horrible MPG as the ECU is pouring fuel unaware that an otherwise *normal* amount of air is entering the engine, its just missing the MAF.
Other possible issues that the ECU will try to 'fix' are, wrong sized injectors for the tune, low/bad fuel pressure, clogged injectors, etc. These situations can cause both + and - Fuel trims..
From there going further into diagnosing the 'health' of your setup you can get into data logging. Which basically grabs a number of data points from various sensors and plots them for you to analyze. Will go into further detail on this:
I'm using the GoPoint BT OBDII dongle thing.
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