Finally Got Diacom Working. Have a Few Q's (long)

[Rufus]

For the 2-bar sensor, DataMaster uses MAP kPa = (0.781 * N) + 8 which gives a range of 8 to 207 kPa. This was determined by measuring actual sensors (see the appendix in the PDF manual for info), as the GM documentation on this is incorrect.

Boost is a guage pressure measurement (not absolute) and the scaling that DataMaster uses is kPg = (0.781 * N ) + 0 which is from the GM datastream documentation.

Note that the GM documentation for boost gain (0.781) agrees exactly with what was measured. The offset is accounted for somewhere in the PCM calculations, and is also compensates for Baro pressure (altitude).

Bottom line, the DataMaster cal values shuld be very accurate, and unless you MAP sensor is kaput should give you reading within 1%. Pressure guages, on the other hand, have very poor accuracy, but also consider that your boost reading is guage pressure, not absolute, so you may have to adjust a bit for altitude.

Regards,

Gary

 

[LuvBoost]

Bottom line, the DataMaster cal values shuld be very accurate, and unless you MAP sensor is kaput should give you reading within 1%.

Just to confirm what you're saying, the DataMaster should not be showing more 14.7? If that's the case I can take the two bar from my Z and install it to test for inaccuracies with the sensor I currently have on the Ty.

 

[Rufus]

Full scale MAP reading (and sensor range) is 207 kPa which is (x 0.14504) 30.03 PSIa which equals (30.02 - 14.70) = 15.32 PSIg. which is very close to the 15.4 PSIg value Datamaster is reporting for boost. May be off +/- 1 bit due to how the PCM makes its calculations -

I do not know if the ECM controls boost based on absolute pressures (which it should...) or guage pressures; it has the information to do it using either method.

If the ECM controls boost based on absolute pressure, and you are at (for instance) 5000 foot elevation, you will see higher boost values for the identical kPa MAP readings! At 5000 feet, standard atmospheric pressure is 84.32 kPa (12.23 PSIa), so the boost guage reading will be increased by 2.47 PSIg - your maximum boost will now be ~17.8 PSIg. - note the absolute pressure has not changed!

Clear as mud?

Gary

 

[LuvBoost]

Hehe, ok that makes perfect sense to me. It sounds like my MAP is sending the proper info. I'm at about 800ft elevation so no major pressure difference there. Thanks for the info!!

 

[Mad Mike]

My diacom file on datamaster program shows my Inj DC at the highest of 148. What does that tell you about my injectors? I'm confused.

 

[smeagol]

Inj DC is something calculated by Datamaster. It is using the commanded pulsewidth reported by the computer and the pulsewidth that would be a static condition at a certain RPM. The computer can command a very high pulsewidth (say 20ms) at 5000rpm, but 12ms is static at 5000rpm. In this case the duty cycle would be 166%. So your injectors are really just operating at 100% DC or static.

The Syty ECM uses a boost reading (or gauge) for boost control actually. It uses this same value for one of the fueling tables as well. It uses absolute map for the rest of the fueling calculations. The barometric pressure is read at startup, and used for the calculation of boost etc; not sure if it is updated any other time. Dig and others have discussed using a separate input for a dedicated 1 bar map sensor to update the baro reading.