fuel trim

jdmspecdc5 · Post by **jdmspecdc5** » Sat Feb 25, 2006 12:01 am

i tuned my car with stock 240 injectors. tune was perfect then when i installed rc 550 injectors and adjusted the fuel trim the car ran very oddly. it would either run super rich (10:1) or really lean (17:1). my tune would not work unless i changed the injector size to 440. any ideas why this is happening?

Djbower1 · Post by **Djbower1** » Sat Feb 25, 2006 3:48 pm

Your base fuel pressure is to high.

Rc Injectors are rated @ 43PSI i Think.

Dan

jdmspecdc5 · Post by **jdmspecdc5** » Sun Feb 26, 2006 1:47 pm

ok i will check that. i think my fuel pressure was around 48psi last time i checked. would a high fuel pressure account for the odd idle? i drove 70miles last night with very minor fuel adjustments and was able to keep a steady 14.3-14.7 a/f the whole time. but then again that was in closed loop.

Djbower1 · Post by **Djbower1** » Sun Feb 26, 2006 2:07 pm

It shouldn't do, But you have now changed the fuel trim and that could of messed something up.

I'm not 100% sure so hopefully someone will offer a second opinion.

Dan

jdmspecdc5 · Post by **jdmspecdc5** » Sun Feb 26, 2006 4:38 pm

tried to do some tuning today but it just seems like i cant get these bigger injectors to work correctly. attached are a couple datalogs and the calibrations i used. the idle surges most of the time and sometimes it will act normal.

setup:
stock b17a1
greddy td05h 18g turbo kit
ngk bkr7e spark plugs
ngk wires

the car ran perfect under boost but since changing the injectors the car has not ran good at all except for cruising on the freeway in open loop.

jdmspecdc5 · Post by **jdmspecdc5** » Mon Feb 27, 2006 2:38 pm

just measured the injectors resistance and these are the results:

rc 550- 12.5 ohm
stock 240- 11.8 ohm

could the difference in resistance be the cause to the problem?

jdmspecdc5 · Post by **jdmspecdc5** » Tue Feb 28, 2006 6:56 pm

tried tunning today. couldn't get the car to run right unless i changed the injector size to 440. anyone know why this is even tho i have 550?

jdmspecdc5 · Post by **jdmspecdc5** » Wed Mar 01, 2006 6:34 pm

finally got the car to run right. i lowered the fuel pressure to about 45psi and played with the overall fuel trim. did some minor tuning adjustments and the car runs great.

siadam · Post by **siadam** » Tue Mar 28, 2006 12:16 pm

What exactly does the "fuel trim" do ?

8)

NeriVtec · Post by **NeriVtec** » Sat Apr 01, 2006 2:42 pm

siadam wrote:What exactly does the "fuel trim" do ?

8)

i would like to know also.

Post by **Spunkster** » Tue Apr 04, 2006 9:36 am

It shifts the vlaues in the fuel tables either up or down without actually changing the numbers...it is like an offset.

jordonking · Post by **jordonking** » Sat Apr 08, 2006 4:12 pm

Thats 45psi with at an idle with Vacuum on FPR... right?