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Interesting Rev 3 ECU information.
http://www.gt4dc.co.uk/forum/viewtopic.php?f=13&t=6863		 Page 1 of 1
Author:  Nibbles [ Tue Dec 10, 2013 11:48 am ]
Post subject:  Interesting Rev 3 ECU information.
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
Author:  TrackToyFour [ Tue Dec 10, 2013 11:47 pm ]
Post subject:  Re: Interesting Rev 3 ECU information.
Interesting post.....not sure exactly what it all means in reality. Needs a universal translator or a cold cloth on the forehead :mrgreen:
Author:  Sirius [ Tue Dec 10, 2013 11:52 pm ]
Post subject:  Re: Interesting Rev 3 ECU information.
Yep very interesting. I'm not sure that any of the measurement kit most of us have fitted will have greater real time accuracy than about 0.1 bar so 1.14 1.15 I don't think there is any real way of telling.
Author:  Diceman [ Wed Dec 11, 2013 10:27 am ]
Post subject:  Re: Interesting Rev 3 ECU information.
Interesting info
There could be a host of reasons. Gearboxes are normally rated for maximum torque capability I thought with only cooling requirements being greater at higher rpm?

I would initially suspect it is more to do with the turbo efficiency and preventing lots of hot air entering the engine.
Author:  Nibbles [ Wed Dec 11, 2013 11:25 am ]
Post subject:  Re: Interesting Rev 3 ECU information.
I've already commented on the MR2 thread that I don't think it's transmission limited.

I think your turbo theory makes sense, but then why would the MR2 not be limited.
Author:  two_OH_five [ Wed Dec 11, 2013 12:30 pm ]
Post subject:  Re: Interesting Rev 3 ECU information.
As the mr2 runs less power it might well be consuming the same amount of air at higher boost than compared to a 4
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