What do fuel trims look like?

mx594 · 11-18-2009, 08:23 PM

I have a UTEC and I have been having trouble tuning it in the 0% column. The stock computer keeps changing things on me and it makes it very hard to determine whether or not the UTEC settings are correct. I understand that you can use Cipher to read the short term and long term fuel trims. I am just curious as to how these trims are displayed? Are there multiple trims for different RPM zones, or is it one global offset value? Can someone post a screenshot showing what they look like with Cipher?

Thanks.

mx594 · 11-20-2009, 08:27 AM

Anyone?

mx594 · 11-23-2009, 05:59 AM

bump

Hal@Dynosty · 11-23-2009, 08:07 AM

The trims are constantly changing, and are based on 100% meaning no trim at all. If it shows 95%, it is subtracting 5% fuel. In this case, you should remove fuel from the 0 column in UTEC.

mx594 · 11-23-2009, 09:43 AM

Thanks Hal.

What I really want to know though is how they are set up. Are they RPM and/or load dependent? In other words, are there different trims for different RPM ranges? For example, is there an RPM vs. Load table that is filled with fuel trims? If so, what are the increments (how many rows and columns). A cipher screenshot of the trims would be worth a thousand words here. I'm just trying to research the subject to determine how useful Cipher will be in tuning my UTEC before I drop $200.

str8dum1 · 11-23-2009, 10:22 AM

on a properly running car, the 0% column should only take a minute or 2 to tune. All all the UTEC maps I made, dialing in 0% was always the easiest.

what do you want to log in Cipher? just logging your AFR will tell you if the changes worked or not.

Hal@Dynosty · 11-23-2009, 10:43 AM

The stock computer has a fuel table and a target AFR table. When it realizes actual AFR does not equal target AFR it adjust/trims +/-. The trims are just floating numbers that are constantly changing/adjusting in an attempt to ensure actual = target.

For what it's worth, I have Cipher monitoring open while tuning UTEC cars. It is helpful to know what the stock computer is doing when adjusting the 0% column. Otherwise, you can +/- the 0 column and see no difference as the stock trims work to maintain the target afr.

mx594 · 11-23-2009, 01:38 PM

Thanks again Hal. I figured that the ecu would store the fuel trims in a table similar to it's fuel table, constantly updating them as you drive and then remembering them for the next time you drive the car. Then it would just multiply cell X from table A (the fuel table) by Cell Y from table B (the "trim table") to get the final injector pulse width. I expected Cipher to let you view this "trim table" as a whole, but it sounds like you can only view the instantaneous trim being applied correct? So Cipher basically displays one number that is considered the "fuel trim" and it changes constantly as you drive (and thus move through different cells in the fuel table)?

I have a custom HKS twin turbo, UTEC, CJM RFS, and DW 600's. I have -12 though the entire 0% column and this is the best I have been able to get it all around. The transition into boost is seamless 90% of the time.

But for whatever reason I have a lean spot right around 2250-2500 rpm that I simply cannot tune out. The car runs very well everywhere else. When I take off from a stop normally, the car will bog right as it passes through this range and the A/F gauge will go full lean for a second. Adding fuel to the 0% column in these zones does absolutely nothing. I also have an issue when cruising under very light throttle at 2250-2500 rpm - the car will lean misfire and start to buck as it jumps back and forth between cruising and decelerating.

Hal@Dynosty · 11-23-2009, 01:53 PM

Sounds like it is unrelated to the 0% column then. It is possible that it is passing through modes in the UTEC - there are a few settings/thresholds in Parameters that may speak to this. One of the difficulties of utec is trying to figure out how to get it to drive smoothly.

mx594 · 11-23-2009, 09:36 PM

Quote:

Originally Posted by Hal@IP

Sounds like it is unrelated to the 0% column then. It is possible that it is passing through modes in the UTEC - there are a few settings/thresholds in Parameters that may speak to this. One of the difficulties of utec is trying to figure out how to get it to drive smoothly.

I have tried many things, I don't think it is my parameter settings. My open loop rpm threshold is 500 rpm, so as soon as it goes into positive pressure at any rpm it goes into open loop. That is the only fuelling related RPM threshold.