I have been reading extensively lately about tuning and the Power FC. I will start by saying I am not here to upset the apple cart or for that matter, don’t shoot the messenger, but I believe that all of the recalibrating of the stock MAP sensor or even the GM 3-bar sensor is being done wrong.
I was thinking that the Apexi engineers developing the first Power FC would have been very careful in developing the lookup table for RPM vs. boost, since any engine near the margin could go bye bye with any significant miscalculations. Of everything they were doing, including all the correction factors for fuel temp, water temp, etc. were probably less important when it comes to fuel at high boost when you don’t know what your real boost is. How did they get the stock MAP sensor input wrong and underestimate boost in their table. You know what, they didn’t get it wrong!

Datalogit then comes along and develops the FC-Datalogit and Commander to allow us to change all of those Apexi base map settings. The PC Commander reads out boost in kg/cm2, it says on the commander itself and in the commander manual. Everyone therefore assumes that FC-Datalogit does the same. Not so fast people. The manual never mentions the unit for PIM in the written instructions or does it? Most of us probably just blew by the chart provided to explain the table. Look at it now from the 2002 manual, page 60.

See attachment below.


The datalogit software and therefore Apexi uses BAR not kg/cm2 for the PIM. It is right here in the manual. Look at the Y-axis unit (bar x 10,000). This changes everything. If you use bar for PIM and look at all the threads about recalibrating the MAP sensor and the low values everybody claims to have gotten for PIM, they are no longer very low and many of them I recalculated are spot on. If what I believe to be true is indeed correct, then all of the recalibrations done are WRONG by using kg/cm2 rather than bar. The Apexi engineers and the Datalogit engineers were right all along.

Please let me know if you think I am wrong, but to me the datalogit manual says I am right. If this is true, we will all need to recalibrate our previous recalibrated MAP sensors using bar. The standard settings for the GM 3-bar will also have to change.

Thanks for looking at this and please let me know what you all think. If am wrong, I want to know.

Mike
30 years of 7’s (1980, 1986 and currently 1994)

 

I'll say this. It seems like the PFC has 4 different pressure units displayed in various places.

mmHg for vacuum: seen on the Commander and in the Monitor window
kg/cm^2 for manifold boost: seen on the Commander

now here's where things get confusing.

If you log "Basic boost" in the Datalogit software, your boost level will typically be between 0-100 . That would imply that the units are in kPA, a very common unit used in all sorts of OEM engine management systems. And yet, if you are in vacuum it looks like you are getting mmHg .

for PIM, which I'm pretty sure stands for "Pressure Intake Manifold" based on documents I've seen for Toyota technician training, it doesn't seem to exactly match any of the other three units I've described above.

BUT I haven't studied the issue as extensively as guys like Chuck have. There may be sampling issues involved when using the Datalogit, because "Basic" seems to be sampled at a slightly different point than "Advanced" , and boosting by nature occurs during transients in normal road driving. If you can sample all the data in a steady state (basically, on a loading dyno holding the cruise control) then you could figure it out better.

I certainly won't come out and say you're wrong about the original scaling intending to be based on bar. In fact I applaud your thinking and desire to investigate.

Where I will I disagree is with your statement "we will all need to recalibrate our previous recalibrated MAP sensors using bar. The standard settings for the GM 3-bar will also have to change"

I've used the original FD MAP sensor & scaling. I've helped others use recalibrated FD MAP sensors. I've used various calibrations on the GM 3 bar. The thing to remember about the PFC is that in the end it's just a bunch of lookup tables. The Power FC is not a model-based engine management system; physical units are not as important as you think. This is especially true considering that the PFC doesn't even have barometric pressure compensation.

Basically, if your various maps and settings are for the most part achieving your desired result, the exactness of the MAP sensor scaling isn't that important for most applications. It becomes more a matter of preference than an imperative.

 

I agree with everything you said arghx. Where I do somewhat disagree is with recalibrating the MAP sensors. Yes, it will not make a difference in tuning since it is just a lookup table, but I do routinely look at the commander, as I am sure many people do, to see the max boost levels to make sure everything is working correctly and I am not overboosting. It would be nice to see the value given to actually be correct for a change and in sync with my boost gauge so it all jives. If using the old calibrations, the commander boost will never be correct.

 

The PFC manual on page 20 states that a pressure value of 20,000 = 2.0 kg/ccm2 absolute.
Thus (2 * 14.22) - 14.7 = a relative pressure of 13.74 psi. The Commander also displays pressure in kg/ccm2. Thus I believe Apexi!

Another issue is that the stock Apexi map sensor values are wrong according to the DL. Apply a fixed known pressure to the map sensor and read the PIM.
Even if you use Bar to calculated the pressure (14.5 > 14.33) the pressure is still low. ONE BIG MESS.

With a DL that has been Map Sensor calibrated using kg/ccm2, take the DL logged boost and divide it by 100 then multiply by 14.22 and you get accurate boost.
It all works perfectly after calibration.

 

One last thing and not to beat a dead horse in the ground, but in reply to cewrx7r1's statement:

> > With a DL that has been Map Sensor calibrated using kg/ccm2, take the DL logged boost and divide it by 100 then multiply by 14.22 and you get accurate boost.
> > It all works perfectly after calibration.

If you recalibrate with kg/cm2 you will shift the plot upward on the chart and then your reading on the DL will be multiplied by 14.22. If you use bar, the plot will be lower, but the same amount as the difference between kg/cm2 and bar. Recalibrated to bar, the reading on the DL will be multiplied by 14.5 and the final result or number will be exactly the same. The same exact number and the same accurate boost since in both cases since you recalibrate to an accurate boost gauge(mine is 4" with 0.5% accuracy to 30 psi) and not a cheap auto gauge with 2% error or greater.

 

Just an update. I performed a recalibration of my new 3bar GM MAP sensor yesterday. Interesting results at least for my car. The standard many people use for scale matches the 6300 setting for BAR and matches 6420 for kg/cm2. Unfortunately, for at least my car, it requires a negative offset of -380 for both in order to totally match up, which is not possible as far as I now for the datalogit(positive numbers only). So using either unit, I will not achieve an accurate boost readout on the commander and I will always be about .5 psi off on PIM. If anyone is interested, the screenshots will be attached below for both. Does anyone know of any way around the negative offset?

 

I plan to re-calibrate my fairly new Apexi 3 bar today using both ways and log both ways at 16 psi. Then I will check the Commander boost vs logged boost vs logged PIM to see what happens.
Results will be posted.

 

Used both the BAR and Kg/Ccm2 map calibration programs today.

The Kg/Ccm2 one won out on accuracy for the displayed boost on the commander which is the same as the recorded basic boost!