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Coolant Temperature Fuel Trims

How to tune warm up fuel maps

Contributed By: enginebasics.com

 

Coolant Temperature Fuel Trims

While there is a lot that could be said about tuning fuel trims during the warm up of a motor, it can be best explained just by understand what’s going on at cool temperatures.

First is to understand that fuel doesn’t atomize as well when it is injected into a cold environment…..meaning it doesn’t mix well with the air. Because of this known fact it is harder to ignite the fuel when it hasn’t mixed well. To compensate for this the fuel tables must be modified on cold start of a vehicle.

There should be a modify table to modify the injector output based on coolant temperature. Once you find this table you should scale it to add fuel the colder the engine temperature is. Again this will take some time and dialing in on your part, but for starters you can start with 0 modification from 180 degrees F and hotter. You will then go from 180 degrees F to 0 degrees adding fuel as the coolant temperature gets colder. As a starting point set 0 degrees to add 30% fuel and extrapolate that value all the way to the 180 degree mark till you are at 0% modification for the 180 degrees F.

While this is a pretty crude explanation it will get you going, and hopefully you understand why you must add so much fuel to get a cold motor started. So don’t be surprised when the A/F value’s are in the low 11’s during warm up. That is just fine. The tuning should then slowly pull the fuel to be idling at stoic by the time the car is warmed up and at 180 degrees.

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