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awdavis01

OBD2 Acceleration Value by Cylinder

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2011 Expedition XLT / 5.4L / 220k

Does anyone have any experience tracking/interpreting the Ford acceleration value per cylinder (Cyl_1_accl, Cyl_2_accl, etc.) calculated in the PCM and measured via the crank sensor?

>>> What is a normal range of values returned when looking at any particular cylinder?

>>> Should the data from all eight cylinders be roughly in parallel with each other on a graph, or will each cylinder generate a completely different trace line on a graph (as shown below)

This is a screenshot of a recent trace I made. The bottom line represent what gear was in effect as the trace developed.

What I have might be perfectly normal, I just don't know what 'normal' looks like.

 

Thanks!

Picture1.png

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Without a frame of reference (actual RPM drop + or -), that is basically useless, especially since the traces are out of firing order and the time sample size is too large for adequate misfire monitoring. It would appear to me that it is also flat wrong as you are accelerating the vehicle, so the cylinder acceleration should *all* be positive. 

  

Is there something you're trying to diagnose?  

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5 hours ago, YT90SC said:

Without a frame of reference (actual RPM drop + or -), that is basically useless, especially since the traces are out of firing order and the time sample size is too large for adequate misfire monitoring. It would appear to me that it is also flat wrong as you are accelerating the vehicle, so the cylinder acceleration should *all* be positive. 

  

Is there something you're trying to diagnose?  

 

YT90SC - You actually provided a lot of good information simply by pointing out the various factors that are missing and how to properly sequence the data.  I'm working on a small, irregular but constant,  pulse in acceleration through all gears under load and a slight loss of torque in 2nd and 3rd.  It's a very slight irregular pulse (no bucking) and I've spent quite a bit of time analyzing other aspects of the vehicle with FORScan to rule out other issues.  My main challenge isn't understanding where the data (of whatever type) is coming from and why, it's not knowing what a 'normal' trace looks like.  You've helped already with the 'normal' aspect via your comments.  

 

I'll do another trace, properly sequenced/timed with RPM included sometime this coming week and post for further comment.  This might be normal wear/tear on a 220k motor,  but I have always been proactive with maintenance and enjoy the analysis aspects of tools like FORScan.

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