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MAF testing 101
Posted to Technical Tips Forum on 6/6/2012 32 Replies

There has been a number of methods that have been discussed for testing underreporting MAF sensors. Certainly having more then one method to test a MAF sensor adds extra tooling in your tool box. Here is a method I have found to work very well when checking a MAF sensor. This method is used once you have done some preliminary diagnosis and you are speculating you might have a skewed MAF sensor. The test involves graphing 2 Pids (STFT-Short term fuel trim) and (RPM) the test is done during light cruise speeds at gentle throttle tip In's below 3000 rpm. While monitoring the graphed data pids if the Short term fuel trim is mirroring the RPM I have found this indicates a skewed MAF sensor and will require replacement as this example shows

[2001 Toyota Camry LE, ECM/Inputs/Outputs Scan Data]

here is another example

[2001 Toyota Camry LE, ECM/Inputs/Outputs Scan Data]

Keep in mind the throttle tip In's must be made below approx. 3000 rpm otherwise the mirroring effect between the 2 pids will not mimic one and other. Here is an example of why this test must be done below 3000 RPM.

[2001 Toyota Camry LE, ECM/Inputs/Outputs Scan Data]

This method is a quick and simple testing procedure and I have found it simply allot faster then using a VE calculator and/or graphing numerous pids to examine after a test drive. However please remember using those other methods along with this one can certainly aid in conclusively determining if you have a skewed maf sensor... consider this method as adding another tool to the tool box.

Here is the after capture on the above vehicle with a new Toyota MAF sensor

[2001 Toyota Camry LE, ECM/Inputs/Outputs Scan Data]

Kevin from Manitoba

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