Fuel Injector Data

Injector Latency

Tuning Tips – Most fuel injector manufacturers will be able to provide you with injector latencies by voltage. The drivers used to develop these latencies may be different than the injector drivers in the stock ECU, so further modification from the published values may be necessary and you should not be concerned if your final values differ from manufacturer documentation.

One way to find the correct latency (or at least the latency that works best with the injector drivers in the ECU and your particular injectors) is to begin with stock fuel pressure and the stock intake system, then set the proper scale value for the injectors you are using based of the scalar calculation. Once you have established a proper injector scalar value, start the engine and let the car warm up (coolant temperature between 170-200˚ F and intake air temperature +/- 15 degrees F of ambient temperature) then re-set the ECU so your fuel trims start at zero. Then, start the vehicle again and watch the SUM of your fuel trims, STFT + LTFT. If you see that the SUM of your fuel trims (STFT + LTFT) is positive, add injector latency until you see the SUM of your fuel trims come closer to zero. You will have to test this throughout the operating range of the engine. Try to avoid sudden throttle movements during this process to avoid corrections based on the Tip-in Enrichment tables. If you see that the SUM of your fuel trims is negative, reduce injector latency until you see the SUM of your fuel trims come closer to zero. Again, you will have to test this throughout the operating range of the engine - the entire MAF curve. Try to avoid sudden throttle movements during this process to avoid corrections based on the Tip-in Enrichment tables.

This is part of a calibration process that will bring you closer to the ideal settings necessary to properly control your fuel injectors. Please take into account that you will most likely have to calibrate the fuel correction maps to get the trims where you want them at different operating conditions.

Injector Scaling

Tuning Tips – In order to calculate the injector open time Porsche uses a large equation to come to the final value. In this equation they calculate air density as well as a slew of other variables. One of these variables is calculating an injector constant with n-heptane. Since some injector companies don't use this as a calibration medium anymore, this can sway the final result of the injector scaling since the density of the two fluids is different. So depending on injector manufacturer you may need to adjust the scaling either up or down to come to a value that is close according to the fuel trims.

With that being said here is the best way to come up with the proper value range for larger injectors:
Y= 44.0901/X so in order to get a new injector constant value divide 44.0901 by your injector size.
Example- Injector Constant= 44.0901/1000(cc)
Injector Constant= .04409 or about .045.

Make sure to check your short term fuel trims at idle after scaling to make sure it is close. Make adjustments if they are not within your target short term fuel trim.

COBB Customer Support Contact Info

Customer Support

support@cobbtuning.com

Phone support available 9am to 6pm Monday-Thursday. 9am to 4pm Friday (CST)

866.922.3059

Return to COBBTuning.com