Originally Posted by mikesevo8

If it helps, here is the specific info from the evo manual:

DTC P0172: SYSTEM TOO RICH
.
System too Rich Circuit
• Refer to, DTC P0201 − P0204 Injector Circuit Malfunction P.13A-267.
.
CIRCUIT OPERATION
• Refer to, DTC P0201 − P0204 Injector Circuit Malfunction P.13A-267.
.
TECHNICAL DESCRIPTION
• If a malfunction occurs in the fuel system, the fuel trim value becomes too small.
• The ECM checks whether the fuel trim value is within a specified range.
.
DTC SET CONDITIONS
Check Condition 1
• Under the closed loop air/fuel ratio control.
• Engine coolant temperature is higher than 77°C (171°F).
• Volume airflow sensor output frequency is 56 Hz or more.
Judgment Criteria
• Long-term fuel trim has continued to be lower than −12.5 percent for 5 seconds.
or
• Short-term fuel trim has continued to be lower than −10 percent for 5 seconds.

Check Condition 2
• Under the closed loop air/fuel ratio control.
• Engine coolant temperature is higher than 77°C (171°F).
• Volume airflow sensor output frequency is 56 Hz or less.
Judgment Criteria
• Long-term fuel trim has continued to be lower than −12.5 percent for 5 seconds.
or
• Short-term fuel trim has continued to be lower than −15.0 percent for 5 seconds.

Check Condition 3
• Engine coolant temperature is higher than 77°C (171°F).
• Under the closed loop air/fuel ratio control.
Judgment Criteria
• Long-term fuel trim has continued to be −12.5 percent for 5 seconds.
or
• Short-term fuel trim has continued to be −25.0 percent for 5 seconds.
.
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are: )
• Volume airflow sensor failed.
• Injector failed.
• Incorrect fuel pressure.
• Engine coolant temperature sensor failed.
• Intake air temperature sensor failed.
• Barometric pressure sensor failed.
• Harness damage in injector circuit, or connector damage.
• ECM failed.

Originally Posted by Phenix_fyah

Injector needs to be scaled and voltage latency needs to be adjusted to get the STFT correct.

Originally Posted by Phenix_fyah

Short Term Fuel Trims