Increased Displacement Effects On Fuel Trims
02-21-2023, 08:45 AM
#1
Increased Displacement Effects On Fuel Trims
I can’t really find any data on this, to keep it simple if displacement is increased, 3.4-3.8, would the fuel trims increase from factory settings?
FRA 1/2- 1.13 1.13
RKAT 1/2- .66 .66
A big thanks to Amargari for posing the question on another thread, just trying maybe get more responses with a better title.
Thanks!!!
FRA 1/2- 1.13 1.13
RKAT 1/2- .66 .66
A big thanks to Amargari for posing the question on another thread, just trying maybe get more responses with a better title.
Thanks!!!
02-21-2023, 07:57 PM
#2
Racer
I'm not an expert, but I would guess yes. If you are letting in more air, then you need more fuel to keep the air/fuel ratio correct.
This is what I believe the FRA and RKAT numbers represent. If I am wrong, please someone correct me.
BTW I have a 4.0 with a GT3 throttle body and here are my numbers. I don't believe that I have a vacuum leak because I smoked tested the engine after installation. I also have brand-new injectors.
RKAT = 2.34 - 2.39
FRA = 1.00 - 1.04
This is what I believe the FRA and RKAT numbers represent. If I am wrong, please someone correct me.
- FRA is fuel trim adaptation under load. A value of 1 means that the amount of fuel being introduced by the injector matches what the reference table is expecting when the car is driving (not idling). Anything over 1 means it is adding fuel. Anything under 1 means it is removing fuel.
- RKAT is the Fuel trim when the engine is at idle. For RKAT you want around “0”. If it is below “0”, the car is running rich at idle and it is taking away fuel in the Idle range. If it is above “0” the car is running lean and it is adding fuel at the idle range.
BTW I have a 4.0 with a GT3 throttle body and here are my numbers. I don't believe that I have a vacuum leak because I smoked tested the engine after installation. I also have brand-new injectors.
RKAT = 2.34 - 2.39
FRA = 1.00 - 1.04
02-21-2023, 08:03 PM
#3
Racer
I'm not an expert, but I would guess yes. If you are letting in more air, then you need more fuel to keep the air/fuel ratio correct.
This is what I believe the FRA and RKAT numbers represent. If I am wrong, please someone correct me.
BTW I have a 4.0 with a GT3 throttle body and here are my numbers. I don't believe that I have a vacuum leak because I smoked tested the engine after installation. I also have brand-new injectors.
RKAT = 2.34 - 2.39
FRA = 1.00 - 1.04
This is what I believe the FRA and RKAT numbers represent. If I am wrong, please someone correct me.
- FRA is fuel trim adaptation under load. A value of 1 means that the amount of fuel being introduced by the injector matches what the reference table is expecting when the car is driving (not idling). Anything over 1 means it is adding fuel. Anything under 1 means it is removing fuel.
- RKAT is the Fuel trim when the engine is at idle. For RKAT you want around “0”. If it is below “0”, the car is running rich at idle and it is taking away fuel in the Idle range. If it is above “0” the car is running lean and it is adding fuel at the idle range.
BTW I have a 4.0 with a GT3 throttle body and here are my numbers. I don't believe that I have a vacuum leak because I smoked tested the engine after installation. I also have brand-new injectors.
RKAT = 2.34 - 2.39
FRA = 1.00 - 1.04
The MAF will measure the greater amount of air being sucked into the bored-out engine and the DME will inject fuel accordingly. From what I've read on here, the DME can compensate and doesn't require re-calibration of fuel and/or timing maps.
Compensation for increased displacement cannot be done via long term fuel adjustment as that is limited to 3% before a CEL is shown and 3.4->3.8 requires 10% more fuel (on average).
As such and in your case any compensation by the DME points towards either too much air or too much fuel and requires identifying and removing the cause.
Compensation for increased displacement cannot be done via long term fuel adjustment as that is limited to 3% before a CEL is shown and 3.4->3.8 requires 10% more fuel (on average).
As such and in your case any compensation by the DME points towards either too much air or too much fuel and requires identifying and removing the cause.
02-21-2023, 08:35 PM
#5
Racer