Episode 1: [LINK]

Time and scale. That is the difference between having a number posted on a thread, and seeing a graph. If somebody were to log on and say "I have low power and my ICP is 480 PSI.", I would have to reply that 480 PSI ICP is perfectly normal at idle, and I would need to see the ICP/IPR performance over time with a Wide Open Throttle (WOT - preferably up a steep grade). Seeing how high the readings get is a matter of scale. Many OBDII apps have default scales on things, because they work with other vehicles. Our top RPM should be about 3200-3300 RPM, but putting that on a scale of 6000 RPM makes the graph line look a little flat.

Because of this scaling discrepancy, I have a habit of sharing the proper scaling in any list of PIDs I suggest to monitor. Fuel Injector Pulse Width is one of the Seven Deadly Sins on a graph. We are dealing with numbers of scales of 0-100 (like IPR percent and MPH), 0-250 (like EOT and TFT), and 0-3500 (ICP and RPM) - then here comes FIPW in milliseconds on a scale of 0-6. I don't know how many times I've squinted at that inchworm-ish FIPW line at the bottom of a scale of 0-100, and I can't suss out what the FIPW is. As a solution, it is sometimes better to program your OBDII software to read the FIPW in Microseconds (Milliseconds times 1000). While the FIPW can go as high as 6000 microseconds while cranking, a stock tune (or a properly configured performance tune) won't push the FIPW much past 3000 microseconds while driving. This means the FIPW can share the same scale as ICP and RPM - making it very readable indeed. Every app I've seen has the ability to change the scaling on every PID.

More on scaling: The MAP sensor max is under 50 PSI, where the EBP sensor max is under 55 PSI. Setting those two gauges at their appropriate maxes works great on a gauge - but completely blows on a graph. The difference in scaling alters how the lines look when comparing two related PIDs. EBP and MAP separate when you've exceeded the envelope of the turbo or there is an air problem, and you really need to see this separation. Differing scales "flatten" the discrepancy, possibly tricking you into thinking all is well if you just glance at the graph. I like it better when problems grab hold of my eyeballs and give them a good yank.

I apologize up front - I'm low on time this morning, so I'm missing one graph. I'll post it later, though.

Here is an example of using the gauge scaling for the graph:



The EBP and the MAP look to be in sync, which is fantastic - but it's fiction. Look at the numbers - there is a separation of close to 15 PSI at one point. Yuck. There should be more boost at that EBP, but scaling on the graph says to our eyes "Nothing to see here folks, move along." - and very few people stare to absorb the details of what's going on.

Let's play with time just for a sec... because I mentioned it at the top of the post. The graph above is a sliver of time with a few PIDs - to really focus on a single event. You can see great detail, and grasp what's happening. A Boy Scout would try to start a fire with slivers... and this is what happens when one tries to start something with a whole freaking log: