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AFR Problems Subaru GC8 EJ20T

Jose Andrinich

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Hey guys, i am new here, I bought a Subaru Impreza GT 1998, it is like the WRX but it has less power, only 220hp.

Well the car came with a PossumLink ECU, the problem is that i cant drive on full boost, the AFR is too lean. It has the STD map and also de HIGH map, both are having troubles.


STD map gives me an AFR of 17 and at normal driving it is between 13 and 15 but if i hit the gas it inmeditely goes 16 or 17 and start to fail, this happens at 10psi (lowest) and 16psi (highest)

HIGH map gives me an AFR of 10 and the iddle is super inestable, the car smokes a lot like a diesel engine, when normal driving the car gives AFR between 12 and 14 but when i lift the foot from the gas the iddle goes down to 200-300rpm and sometimes the engine stops. When hard driving, the AFR is between 14 and 15.5 (lean) but it runs better than the STD map. I have only test this map at 12psi, in this case if i lift the foot from the gas the engines always stops.

Need a lot of help! this car is new for me, it is difficult to undestand this G1 ECU i have worked with and 2003 sti and it is much easier.  if anyone has any advise, please let me know.

I can upload both maps if it is necessary.

thank you all! 


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Looking at the MAP the fuel numbers look too big at low load the numbers are so flat going down the table.

It looks to need some time spent tuning.

You can tune in real time so if you drive the car and work through the fuel map starting at light load and working up to higher load.

Try to adjust only when you are in a zone centre.

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  • 2 weeks later...

what is your car running


is it a td04 turbo, black intercooler, grey injectors


if so can supply a map if car standard, as running a g1 link ecu

can supply 6 rows of fuel info, 6 rows of ign info, boost guide, waste gate control

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  • 2 months later...

Hey, thank you all for your replys.


Well i tried to fix the problema, i am not an expert doing this mapping, but here my latest upgrade.

It is a map done by me, working at 15psi. Timing tables hasnt change, just did modificatin to teh fueling.

Please is any of you guys can help me.

Mi Impreza has yellow injectors and HKS air filter, the all the other stuff is OEM. Please Neil send me your values or complete map to upload it to my ECU.

If any of you have time to check my ECU map, please i would like to hear your comments. I guess i need more modification in timing table and also fueling tables.

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link ecu is a g1 unit

can you set it out like the following please


master fuel - 66

fuel map

row1  numbers seperated by commas please

all the way to row 6


same again with ign map


lambda range - full

map sensor - factory

advance limit - 32

map limit - 250kpa

rpm limit - 7000 rpm

wastegate base - 37

wastegate rpm - 2300

wastegate sens - 1

knock base target - 30

knock control - on

closed loop lambda - off

lambda targets table please

ilde, cruise, rows3, rows4, rows 5, rows 6


give me boost table line please 250 to 7750 rpm line


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OK, soy by what i see you can't open my uploaded maps.

Well i will try to send you the info by message.

1998 Subaru Impreza GT, EJ20 engine, td04 turbo, 1998 STI yellow injectors, HKS air filter. G1 POSSUM-LINK ECU.


Im sending you a Word file with the pictures of what i see when i hookup mi laptop to mi ECU.


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basicaly this is my setting:



ROW 1 (15MPa): 104,104,104,106,108,108,110,110,110,97,97,97,97,97,97,97

ROW 2 (45MPa): 105,105,104,104,97,97,98,99,99,99,101,101,101,101,101,101

ROW 3 (75MPa): 105,104,104,98,97,97,99,101,102,102,103,104.

ROW4 (105MPa):125,125,122,116,116,115,

ROW 5 (135MPa):129,129,129,125,123,129,135,136,136,136,136

ROW 6 (165MPa): 128,128,128,128,128,133,131,138, 140, 142

ROW 7 (195MPa):132,132,132,132,132,140,150,152, 152,152,152,152

ROW 8 (225MPa):133,133,133,133,130,143,148,150,151,153,153,152

ROW 9 (255MPa):109,109,109,109,107,116,121,121,121,121,121,121

ROW 10 (280MPa):105,105,105,105,103,112,117,117,117,117,117,117

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you need to let link ecu control the boost


your tps needs calibrated with low tps around 10 and high tps around 100


why does your system volts say 21.6 volts if you are on a 12v dc system


are you a g1 ecu as you have 10 rows of fuel and ign, were my ecu only has 6 rows


can supply details but you would have to fill in some gaps


got two maps


map 1 - td04, sti intercooler, ngk 6's, grey injectors (380cc) around 270nhp on 1.35bar boost with cat downpipe

map 2 - vf28, sti intercooler, ngk 7's, yellow injectors (440cc), ported headers, ported up pipe, no cats, 1.4 bar boost 337bhp

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can you send me both MAPs? so i can check them out?

Here i send you a picture of my ECU BOARD, so you can see what i have, i think it is a G1 anf that but the ex-owner told me too.

The boost you mention in yous maps is total boost? o you have to add the atmospheric pressure to them? Because the manual says maximun 18psi = 1.25bar (aprox)


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Thank you Neil!

I got both maps. Unfortunately i think i can not download them to my ECU.

Now that i have checked them i have more questions. How can you run your WRX with a Base fuel of 70? mine does not even starts! i run mines with 85 on base fuel.

Other question is, why do you have your TPS HIGH at 61 and TPS LOW at 0 ?, i have TPS LOW 253 and HI 61.

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Well i still dont understand how to set the TPS. Mine says 253 and 61 for low and high. Actually im living in Peru in a city that is about 2500 metres above sea level, from what i know i should use less fuel than anybody that is in the coast, but as i told you my car wont work with less than 80 as a base fuel, last night i tried to put 70 and start the engine but it did not work. My car has the oem td04 turbo, yellow sti injectors (440cc) and a bosh fuel pump that i think it is the same as the oem, same fuel pressure (42psi) and same pumping capacity (180lph).

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  • 2 weeks later...

On the hand control the TPS set up will be easier then on the PC.

You can just use the adjust keys with throttle closed and then open to get 10 - 100.

Once done make sure you do a store.

A "Pill" Is only required if you are using a two port boost control solenoid.

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