NewbieWar

Okay, so I'm a little perplexed here, i'm just learning...
1st column Off-Idle, 2nd At-Idle
Cyl 1 1.03 1.06
Cyl 8 0.98 0.95
Cyl 4 1.02 0.95
Cyl 3 1.02 1.00
Cyl 6 0.99 0.98
Cyl 5 0.97 0.95
Cyl 7 0.98 0.94
Cyl 2 1.02 1.08

I always forget which cyl is where... but doesnt matter here,

why would cyl 4 flip flop from not using as much fuel as the others cylinders during idle, then require more fuel than others when not at idle... something is not right with that???

NewbieWar

hmm, well I have more to add to this topic...

okay, so passenger side o2 sensor, at .027... thats really lean
and driver side .453... that sounds good to me...

so... what gives? why would one bank be totally in the gutter like that?

spark? fuel? spark delivery? tune?

hmm these two cylinders seem like something is not right...
Cyl 2 is completely different than the whole bank? would I be correct to assume i should check something with that cyl, might be affecting the entire bank?

Cyl 2 1.02 1.08
Cyl 4 1.02 0.95
Cyl 6 0.99 0.98
Cyl 8 0.98 0.95



Cyl 1 1.03 1.06
Cyl 3 1.02 1.00
Cyl 5 0.97 0.95
Cyl 7 0.98 0.94

bobdec

Individual Cyl Fuel Trim Multipliers are values the design engineers determined to balance the differences of input air flow (sort of like volume efficiency) for each cylinder within the intake manifold. At idle values are used with TPS=0% and off idle values are used for TPS less than 14.8% , over 14.8% TPS the table no longer is used. (both values and off idle TPS thresholds are programmable). You will notice the front cylinders closer to the TB air inlet get a few hundredths (.0X%) more fuel than the rear cyls that get a little less air. Your post sounds like you are saying these cylinders are running rich/lean. This is not the case the fuel multipliers +/- are used to assist in keeping the correct AFR by adding/subtracting fuel per cylinder to match the intake air flow design. Buy the way your setting are correct for a stock setup..

sbs

I think, based on this and your other threads, that it would be a good idea for you to not touch tunercats until you have some basic understanding of how EFI, datalogging, and tuning work.

NewbieWar

i'm getting that feeling too...
just bought it to turn off my egr sensor anyway...

WS6T3RROR

It has to do with the firing order and the cylinders fighting for what little air does come past the tb blades at idle. What you see in the trims is that cylinders 1 and 2 (the front cyl on each side) get the majority of the air at idle (the rest comes through the iac manifold). What you have to understand is that at idle you've got a big lack of airflow in the manifold, and vacuum pulses from every cylinder affecting what little flow there is.

When you're off idle like cruising along at 60mph what you have is about 3-4x the mass of air available and what you get is sort of a gradient from the front to the back of the engine with the front still getting more air. The values in the off idle table are going to be correct on average for the up to 14% tps that they are in use.

Be aware there are a few different revisions of the cylinder fuel trims. If you do a cam swap it totally changes what goes on inside the intake manifold and they do need adjusting.

You cant just look at one o2 sensor reading to determine whats happening either, and they oscillate very quickly during closed loop operation. You have to use the blm's to determine whats going on during closed loop not o2 millivolts. You especially can't trust the o2 mv on a cold start and especially if you have the cats and air pump still because it will be injecting air into the system and throw things ultra lean.

NewbieWar

this is one thing i was getting at in my other thread, i've got an lt4, with an lt1 tune... and i'm going to keep my grubby hands off the tuner, but i'd like to learn what variables have changed
and what effects what.

obviously the lt4 cam is not a radical cam, but the heads flow a lot better, thats for certain.

Injuneer

I don't think you have any idea what you really own. You've admitted elsewhere, its an LT4 because the seller told you it was an LT4 and it has a red intake.... but you know the previous owner lied to you about other things, including having an LT4 Corvette trans (ZF 6-speed) and LT4 Corvette rear axle (full IRS).

You need to figure out what you have. You need to figure out what all the loose connectors are that you have asked numerous other threads about. You need to focus on the basics, not question the GM engineers for setting the trims the way they did.

Why would an O2 sensor reading a constant .453V "sound good"? As I explained in your LT1 Based Engine Tech forum question, it sounds like your left O2 is either unplugged, ice cold or deceased.

You quote from my guide to interpreting scanner data, but it appears you really didn't understand anything I wrote. People are trying to help you, but you are going in 10 different directions at once, without even knowing what engine you have in your car. Pull the intake manifold and head part #'s to see if they are even LT4 parts.

Harsh words, but someone needs to wake you up.