Ok, you guys convinced me to bite the bullet and jump in to doing my own chip, so now here comes the dumb questions.

I'm working on a stock L03/305 from a '91 Caprice, the plan is to first learn tuning on this stock motor and then dump in a 383 and have some real fun.

I'm using TunerPro RT for both editing and logging with .xdl and .ads files for the Caprices 16136965 that are available from the moates.net site.

Thanks a lot to Mark Mansur of TunerPro who found and fixed some problems in that .ads file that were making the logging not work right. It appears to me that this .ads file was a first shot by somebody and I think it still has some additional problems that need to be worked out as shown below with the MAP value display.

As a first step I'm logging the engine during idle and trying to get an understanding of that phase first.

One thing that looks funny is that during idle at around 650 RPM the MAP voltage value is being reported as around 1.18 volts, which I understand is a normal MAP voltage output for idle, but the display MAP value is being shown as around 10.8kPa, which has to be wrong.

The .aps file uses the following formula to convert the voltage to MAP:

MAP = 0.007232 x binary val + 10.354

I've also seen this formula posted other places, so it must be right for some kind of MAP sensors, but for my type sensor it appears to be wrong.

However in a recent post RFMaster posted the following table:

kPa |----| in-Hg |----| VacVmap
100 |----| 0.0 |----| 4.90
95 |----| -1.5 |----| 4.62
90 |----| -3.0 |----| 4.35
85 |----| -4.4 |----| 4.08
80 |----| -5.9 |----| 3.80
75 |----| -7.4 |----| 3.53
70 |----| -8.9 |----| 3.26
65 |----| -10.3 |----| 2.98
60 |----| -11.8 |----| 2.71
55 |----| -13.3 |----| 2.44
50 |----| -14.8 |----| 2.16
45 |----| -16.2 |----| 1.89
40 |----| -17.7 |----| 1.62
35 |----| -19.2 |----| 1.34
30 |----| -20.7 |----| 1.07
25 |----| -22.1 |----| 0.80
20 |----| -23.6 |----| 0.52

This table looks like its probably the right one for my MAP sensor as it would put my idle MAP around 30 which makes more sense.

Does anyone know the correct conversion formula from voltage to MAP for this second kind of sensor?

Thanks,

Paul T.

 

I figured this out by taking a look at some other .ads files. In the Caprice .ads file the constant was wrong, the correct formula is:

MAP(kPa) = (0.369 x N) + 10.354

Where N = (Volts/5) * 255

The Caprice file had a different constant than .369 for some reason.

With the constant corrected, the MAP values and the sensor voltages are consist with RFmasters table I copied in the previous post.

In my stock L03/305 I'm seeing an idle map of around 32kpa at 650 RPM, I'm and old timer more used to vacuum values but that MAP seems about right for idle, correct?

Paul T.

 

https://www.thirdgen.org/forums/diy-...le#post2678001

 

There are different MAP sensors out there. I do not recall if I have posted all my measurement data. Basically I used JY pulled GM MAP sensors. First was '460' with green insert and second one '835' with a red insert.

In kPA
MAP 460 - Vmap= 0.05467 * (kPa) - 0.57024
MAP 835 - Vmap= 0.054397 * (kPa) - 0.72709

in in-Hg
in-Hg 460 - Vmap= -.18476 * (in-Hg) + 4.8937
in-Hg 835 - Vmap= -.18421 * (in-Hg) + 4.7126

If your engine is idling at indicated 32 kPA then, depending on MAP sensor
MAP 460 - Vmap= 1.18 Vdc
MAP 835 - Vmap= 1.01 Vdc

You can insert a vacuum gauge and measure vacuum directly and determine which of the two MAP sensors you have. BTW 32 KPA is about 20 in-Hg which is very healthy idle vacuum. I hope this helps.

//RF

 

RFmaster-

Thanks a ton for that detailed MAP info, that's very helpful.

This forum kicks rear!!!

Paul T.