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Discussion Starter · #1 ·
I've been searching for the last week for information about remapping this damn GEMS 8 ecu. It seems to either be some closely guarded secret, or nobody has really taken the time to do it..

The Megasquirt route seems like more trouble than it's worth, and it's not OBDII compliant. (I get to live in a GREEN state)
Also, you don't really have any of the OEM safeguards in there...

Paying over $500 for a cookie cutter "chip" doesn't seem to be worth it either.

I've remapped tons of other ECUs.... And just started diving into this one.

Any input / collaboration from anyone else who would like to work on this with me would be greatly appricated!

Here's what i've got so far.....

2 eproms - most seem to be the write-once type.
27C512 and 27C1001 eproms.

27C512 Eprom seems to have 2 fuel maps in it (open / closed loop?)
map1: 55D9 - 56D9 16x16, 8-bit map
map2: 56E1 - 57E1 16x16, 8-bit map

27C1001 Eprom seems to have the ignition table towards the end of the rom
ign: 13AEA - 13BEA 16x16, 8-bit map

That's all i've come up with thus far...
I'd love to compare the bin files from these eproms to some others.
I hear that the range rover with the GEMS ecu has a higher output...

So, please post any maps / roms / bin files you may have!

Hell, if I come up with a good, useful remap for this GEMS ecu, i'd sell it for more like $20-$30... not $500+

And it seems like most of these places that are selling these chips are just modifying the timing table - a few of them only seem to replace the 27C1001.

I'd like to conquer both chips... take care of the lean area while cruising, maybe get a little better MPG, and get a bit more grunt on the bottom end...

13 Posts
I am interested, but have no idea how to access my ECU. I am swapping my 4.0 to a 4.6 so I am definitely interested in ECU remapping for the change.

Side question. Can I just purchased a used 4.6L ECU and swap it in my 4.0l ? Are the plugs the same? and would the vin # change? I am not sure if the vin # is tied to the ECU, just don't want to fail smog when the vin # doesn't match the car when the OBD II is plugged in displaying another vehicle.
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