Why does factory ECU lean in high gears/speeds?
12-05-13, 07:32 AM
#1
Why does factory ECU lean in high gears/speeds?
I'm tuning a nitrous system and I'm wondering why the hell the factory ECU goes leaner in higher gears?
Basically in 1st-3rd gear, when WOT the A/F ratios can get into the 11s, but in 4th and 5th they are in the 13.5 range. It seems the ECU is doing something based on how fast the car is going (MPH) since there's not a "what gear am I in?" sensor.
This is a problem for running wet N2O without a progressive controller because you have a fixed amount of fuel delivery throughout the curve so if the ECU is trimming fuel you can't run an optimal spray mixture in 4th and 5th (particularly 5th) safely.
I'm putting in a fuel pressure gauge this week and am curious to see what the hell it's doing.
Basically in 1st-3rd gear, when WOT the A/F ratios can get into the 11s, but in 4th and 5th they are in the 13.5 range. It seems the ECU is doing something based on how fast the car is going (MPH) since there's not a "what gear am I in?" sensor.
This is a problem for running wet N2O without a progressive controller because you have a fixed amount of fuel delivery throughout the curve so if the ECU is trimming fuel you can't run an optimal spray mixture in 4th and 5th (particularly 5th) safely.
I'm putting in a fuel pressure gauge this week and am curious to see what the hell it's doing.
12-05-13, 11:31 AM
#2
WOT is open loop and it looks up tables to inject fuel, that is just what the factory tune is for probably the 13.5 range and then they put extra fuel in the lower ranges for extra torque most likely.
It is a problem, but you can solve it by assuming your mixture will always be at its leanest point aka 13.5 and then tune the N2O according to that. Sure you will run extra rich in the lower areas and not as optimal of a spray, but thats not as much as a problem as running lean on top which could literally bring it to a grinding stop. Also it matters where you plan on spraying but if it involves 4-5 then tune for that.
The stock fuel pressure regulator is a 1:1 rate regulator with a base pressure just around or under 40 I think.
I don't have alot of experience with N2O, but lots with the stock ecu. you can try a fuel controller but to hae it perfect and reliable you may want to look into a aem v1 which has full control over all that and also some failsafes.
It is a problem, but you can solve it by assuming your mixture will always be at its leanest point aka 13.5 and then tune the N2O according to that. Sure you will run extra rich in the lower areas and not as optimal of a spray, but thats not as much as a problem as running lean on top which could literally bring it to a grinding stop. Also it matters where you plan on spraying but if it involves 4-5 then tune for that.
The stock fuel pressure regulator is a 1:1 rate regulator with a base pressure just around or under 40 I think.
I don't have alot of experience with N2O, but lots with the stock ecu. you can try a fuel controller but to hae it perfect and reliable you may want to look into a aem v1 which has full control over all that and also some failsafes.
12-09-13, 07:37 PM
#5
Tuning in the 1:1 gear will also help you out. 4th gear for R154 transmissions.
I've never had that issued when I tuned in the correct 1:1 gear.
I've never had that issued when I tuned in the correct 1:1 gear.
Last edited by emoFTW; 12-09-13 at 07:42 PM.
Thread
Thread Starter
Forum
Replies
Last Post
SC300T
Performance & Maintenance
18
09-24-02 09:53 PM