Fuel trim help

kurt · Post by **kurt** » Mon Mar 12, 2007 9:41 pm

I am having some issues with short term fuel trims. I have been fiddling with my part throttle settings so that they will fall within 10 either way but i am still getting some serious short term fuel trims. I have gone almost -15% off the stock IPS K2 low speed fuel map.

What is weird is the fuel adjustment table-map does not show large adjustments being required. I have target lambda set as 14.7 from columns 1-6.

Would appreciate if someone could take a look at my datalog and kal. In this version of the kal, I have gone -5% from 1000-2750 rpm in columns 3-7. Thanks.

Razathorn · Post by **Razathorn** » Wed Mar 14, 2007 9:24 pm

What base map did you start with? The easiest way to get part throttle nice and close initially is to pick a map that has the same manifold, injectors, and cams as you.

Wayne

kurt · Post by **kurt** » Wed Mar 14, 2007 9:34 pm

Someone from another forum actually passed me his kal. Our mods are similar except that he has 440cc injectors while I am still on the stock 310cc ones. I have updated the injector size to reflect that so I am guessing it should not cause any issues.

Razathorn · Post by **Razathorn** » Wed Mar 14, 2007 10:21 pm

kurt wrote:Someone from another forum actually passed me his kal. Our mods are similar except that he has 440cc injectors while I am still on the stock 310cc ones. I have updated the injector size to reflect that so I am guessing it should not cause any issues.

Adjusting the injector size is just a ballpark. Different injector brands and designs flow different amounts of fuel at different loads and duty cycle. You will likely find that you can adjust things fairly well by initially inspecting how much leaner or richer you are at a given rpm point at the various loads and then applying that logic to the rest of the load columns at all rpm points. Then you can see how far off the rpm points are from each other and clean things up by adding or removing fuel across all load columns for the same rpm point (within reason, might wana skip boost columns for example).

The job of part throttle tuning is to allow closed loop to work correctly. I like to see my short term trims anywhere from -10 to 0. Closer to 0 the better, but I'd rather see 0 than + 5%. If your trims are negative, that means on an o2 sensor failure, you will run richer, not leaner, than ideal.

That's how I do it. It's worked fairly well for me. Then again, I rely on closed loop.