From the MR2OC.
jon.sole wrote:
The ST205 ECU has a lower fuel cut at higher revs. The Rev 3 MR2 ECU has the same fuel cut across the rev range.
jon.sole wrote:
Both ECUs have a table of 3 values that controls the fuel cut limit at 3 rev ranges.
On the MR2 ECU the 3 values are the same:
Code:
ROM:C1EF table_boost_limit: .dw 0200h
ROM:C1EF ; Boost cut lookup table
ROM:C1F1 .db 02h
ROM:C1F2 .db 218, 218, 218 ; 255 on TechTom ECUs
ROM:C1F5
On the ST205 the last entry is reduced, which has the effect of reducing fuel cut progressively from 4800rpm to 6400rpm:
Code:
ROM:C1B8 .dw 0200h
ROM:C1BA .db 02h
ROM:C1BB .db 218, 218, 205
I don't know the exact conversion from the raw values in the table to PSI, but it is around a 5% drop at 6400rpm. I'm guessing the lower fuel cut at higher RPM is to protect the transmission.
Modified ECUs with a TechTom board fitted change the values in the table to 255 to effectively remove fuel cut.
shinny wrote:
Assuming 0 means 0V from the map sensor and 255 means 5V and based upon Richard Doig's formulas (
http://gtfour.supras.org.nz/mapsensor.htm) I calculated the MAP sensor's voltages...
1.31bar -> 19psi -> 4.27V -> 218
1.14bar -> 16.5psi -> 4.02V -> 205
That puts the ST205's fuel cut at 1.14 bar, which is lower than I expected! I didn't have trouble running 1.15 bar on my original external wastegate setup and the ST205 ECU, so perhaps Richard's formula is fractionally incorrect?
Edit: This page suggests the ST205 has fuel cut set at 17psi / 1.17bar:
http://k1ano.co.uk/boostcontrol/rvgt4specifics.htm
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