GM 3 bar MAP scale constant / multiplier

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08-19-2018, 01:19 AM
iangoround

GM 3 bar MAP scale constant / multiplier

Now that I've got a reliable way to log, I've noticed that the MAP value reported by the SMEC doesn't match my (fairly accurate) boost/vac gauge. I see ScaleMAPVoltsToPresAddConst and ScaleMAPVoltsToPresMultiplyConst both say they made need to be tweaked for a GM or MSD 3 bar. But....how does one go about tweaking them?
08-20-2018, 07:00 AM
wheming

Re: GM 3 bar MAP scale constant / multiplier

What are they set at stock? 0, & 1?
I checked my MAP reading some time ago with a known pressure and mine was off also.
Sounds like this could help calibrate the MAP, which would be nice to know you are logging accurate readings.
08-20-2018, 05:01 PM
tryingbe

Re: GM 3 bar MAP scale constant / multiplier

I don't think it matters that much.

I mean, the ECU looks at the MAP sensor as something that provides a 0-5 voltage and so long your a/f is ok the entire range, the MAP sensor is working correctly.
08-20-2018, 08:22 PM
iangoround

Re: GM 3 bar MAP scale constant / multiplier

Well, it matters a little when setting boost targets. If the MAP is reporting incorrectly, one could run in to problems where OB shutdown is either hit too early or too late. But mostly it's for accuracy's sake I guess.

Quote:

Originally Posted by tryingbe

I don't think it matters that much.

I mean, the ECU looks at the MAP sensor as something that provides a 0-5 voltage and so long your a/f is ok the entire range, the MAP sensor is working correctly.

- - - Updated - - -

...AddConst is set to 007 and ...MultiplyConst is 09.

Maybe the thing to do is run do a key-on, car-off log with the MAP hooked up to regulated air, and change those values until it reports closer to correct.

Quote:

Originally Posted by wheming

What are they set at stock? 0, & 1?
I checked my MAP reading some time ago with a known pressure and mine was off also.
Sounds like this could help calibrate the MAP, which would be nice to know you are logging accurate readings.
08-20-2018, 08:43 PM
wheming

Re: GM 3 bar MAP scale constant / multiplier

Quote:

Originally Posted by iangoround

Well, it matters a little when setting boost targets. If the MAP is reporting incorrectly, one could run in to problems where OB shutdown is either hit too early or too late. But mostly it's for accuracy's sake I guess.

- - - Updated - - -

...AddConst is set to 007 and ...MultiplyConst is 09.

Maybe the thing to do is run do a key-on, car-off log with the MAP hooked up to regulated air, and change those values until it reports closer to correct.

Yes, this....
But also you need to look at throughout the range.
So if there is small error near 0psi, but greater error at 30psi, then should be able to use the multiplier.
If it was off by 1-2 psi near 0, and the same at 30psi, then should be able to use the other.

That is, if we are understanding the use of those two tables correctly.
08-20-2018, 10:40 PM
tryingbe

Re: GM 3 bar MAP scale constant / multiplier

Quote:

Originally Posted by iangoround

Well, it matters a little when setting boost targets. If the MAP is reporting incorrectly, one could run in to problems where OB shutdown is either hit too early or too late.

I turned all overboost control off every time when I use turbonator.

I gave up using the stock ECU to control boost a long time ago, when you run the boost at 27.9psi, you want boost to be stable.
I now use a HDi boost controller with a low and a high knob to control boost. Fast, easy, and $120 well spent.

http://www.turbo-mopar.com/forums/sh...od!&highlight=
12-17-2018, 10:06 PM
krut

Re: GM 3 bar MAP scale constant / multiplier

This is done through editing the tpl, or through MPTune? - I was looking at this last night trying to figure out how to set the correct slope in case I find some other map sensor laying around, and got a bit confused.