16.4 LTFT after Injector install

**wa04compg** · 06-16-2014

Ok so my fuel trims where within 5% +- with stock injectors. I installed some cobra 39lb injectors and scaled the IFR table according to new injector size. Now at idle and light to moderate throttle fuel trims are pegged at 16.4...when I get into PE drops to 0 like normal my Wideband is also showing me cruising down the road at 14.4 to 14.7 AFR. What am I missing? Did I do something wrong? I sprayed around vacuum lines and didn't change anything. Also noticed at idle the BBV opens and closes every 5 seconds or so...can't say I have ever noticed that before...Please help I am a newb at this tuning business

**darkhorizon** · 06-16-2014

what was your new number you poked into HPT?

**wa04compg** · 06-16-2014

Don't remember off top of my head but hour after I started this thread I dropped the stock ifr numbers back into my tune let it idle for a few mins and fuel trims dropped to within 3% and idled right at 14.7afr...weird sauce so tomorow going to drive around and do some logs

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**wa04compg** · 06-17-2014

Stock IFR table is sloped from 29 to 34...when I first installed the injectors setup the table for 36 to 43 as I remember...going to try do some logs tonight or tomorow

**darkhorizon** · 06-17-2014

should be 34-40

**darkhorizon** · 06-17-2014

with headers/xp cam, you typically will max the trims at idle due to exhaust leaks and cam overlap.

**wa04compg** · 06-17-2014

Yeah it would max them at idle and cruising around only time it would come off 16.4 was when I went 50% throttle or more...I plug in those numbers see how it goes...thanx DH

**wa04compg** · 06-18-2014

34-40 worked great! Couple maf tunes and she is a lot better...thanx darkhorizon!

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**darkhorizon** · 06-19-2014

Stay away from maf tuning. Use the ifr table unless there is something very obvious that you are sure needs to be fixed in the maf table

**91parkave** · 06-19-2014

Why not do a writeup on......why you don't maf tune after changing up components that affect airflow?

**darkhorizon** · 06-19-2014

Because there is nothing to write.

You are not changing the density/mass of the air the maf is reading when you put a cam in.... So why is it you are going to change the table that translates it.

**91parkave** · 06-19-2014

if you're increasing the airflow or the "efficiency" by pulling more air in then then before. The g/sec for that hz rating will not be the same

**darkhorizon** · 06-19-2014

.... if the motor moves more air then the sensor will read the more air coming in... you are not changing the mass of the air with a different cam under the lifters unless you have some sorta laws of physics bending machine inside the cam.

**darkhorizon** · 06-19-2014

I used a maf and a spare ecu to run a flow bench for my buddys head porting deal... its a calibrated sensor so I used the table in the pcm to translate into mass air flow as it was improved or worsened at the head port.

**wa04compg** · 06-19-2014

I readjusted the maf because I dropped pulley sizes and afr wasn't right from setting ifr wrong before

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**darkhorizon** · 06-20-2014

Originally Posted by wa04compg

I readjusted the maf because I dropped pulley sizes and afr wasn't right from setting ifr wrong before

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Yeah, setting it back to stock is the best option.

**wa04compg** · 06-20-2014

How do you achieve your AFR if you don't maf tune

**darkhorizon** · 06-21-2014

It shouldn't need adjustment and if it does you can use pe to adjust things. Youll want to tweak the injectors first to make sure they are close as they can be.