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Injector Dead Time

EFI Tuning Fundamentals

Discussion and questions related to the course EFI Tuning Fundamentals


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Could you please go over more on how you find the dead time?

Lets say your installing ID1000cc to replace stock 532cc.

ECUFlash lets you change Voltage latency and injector scaling.

The EVO's battery voltage likes to hover around 11.73 - 15 volts.

Stock 532 (Injector scaling)

Voltage Latency 11.73 = 1.110, 14.08 = 0.900

I have researched the scaling to be 20-30% less that what the injector size is. So 1000 should start off around 812cc scaling, that correct?

What is the best way to find out what the new Voltage Latency should be? I've been doing it by logging STFT (Front O2) as close to (+-0)

Anyone have any tips?

Thanks!

Deadtime is usually provided from the injector supplier or manufacturer but even then sometimes it needs some tweaking. The way I see ECUFLASH method is trial and error, bunch of forums discuss it. Theres alot of stuff going on in OEM ECU code and alot is unknown when reverse engineering stock code. Thats why advantage of stand alone ecu is that it gives you full control of what is happening. In OEM Flash tuning there might be code running and doing calculations in the background that are unknown. Id say stick with what works and is recommended by others tuning ECUFLASH.

Here is what Cobb's documents say:

Injector Scaler

This table contains a singular value used to represent the fuel injector size or flow rate. Any changes to this value will affect ALL tables within the ECU related to fuel delivery and load calculations. When using stock injectors with Petrol fuel, this value DOES NOT need to be altered. When adjusting this value, a lower number represents an SMALLER injector, whereas a larger scale value will represent a LARGER injector.

Tuning Tips – To calculate a starting value for a different injector size than stock, use the following formula:

New Scale Value = [(New Injector Size * Original Scale Value) / Original Injector Size].

For example, let’s say you are replacing your factory EVO X injectors (~550cc) for aftermarket 750cc injectors. The formula would look like:

New Scale Value = [(750cc * 532) / 550]

New Scale Value = 725

Input the calculated value as a starting Fuel Injector Scaler value. To fine tune the injector scale value, we suggest you install the stock intake system and run with stock level fuel pressure levels. You will want to display the Short-term Fuel Trim and Long-term Fuel Trim values with the Dashboard. With the engine idling at full temperature (coolant temperature between 180-195 F and intake air temperature +/- 15 degrees F of ambient temperature), you can make adjustments to the scale value until the A/F Trim Mimed. + A/F Learned are as close to zero as possible, +/- 5% is generally acceptable. We have seen that you will also need to fine tune the Intake Calibration tables in order to get the calibration closer to optimal. The closer you can get to 0% is ideal. DO NOT attempt to tune for an aftermarket Intake and aftermarket injectors at the same time. An aftermarket intake will affect your A/F Trim Mimed. and LTFT values at idle and part throttle, making it nearly impossible to find an accurate Injector Scale Value. If you have an aftermarket intake please use the above equation to establish your initial Fuel Injector Scale value then proceed to the Intake Calibration section if necessary. If you plan to use an aftermarket intake, it can be installed and the necessary tuning can be performed AFTER you have found the optimal Fuel Injector Scale value.

Injector Latency

This table contains latency values used to tell the ECU how much latency is needed to properly control the fuel injectors; the breakpoints are in battery voltage. All fuel injectors require a certain amount of time to fully open which is referred to as Injector Latency. The amount of latency an injector requires is dependent on several factors such as the size of fuel injectors, viscosity of fuel, manifold pressure, and fuel pressure. Lower battery voltage requires increased injector latency (dead time). Likewise, higher fuel pressure may also increase the injector's latency. The data in this table is represented in milliseconds. A higher value will open the fuel injector sooner, thus the total IPW will be greater; a lower value will open the fuel injector later, thus the total IPW will be less.

Tuning Tips – Most fuel injector manufacturers will be able to provide you with this latency data and the voltage they are referenced at. Although, the drivers used to develop these latencies may be different than the injector drivers in the stock ECU. You can use the published values as a starting point and modify from there. Don't be afraid if your final values differ from what the manufacturer provided. To tune this table, we suggest that you first establish a good Injector Scale value.

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 have your fuel system running stock fuel pressure and have the stock intake system installed then;

1st - set the proper scale value for the injectors you are using based of the scaler calculation.

2nd - start the engine and let the car warm up to temperature (coolant temperature between 180-195 F and intake air temperature +/- 15 degrees F of ambient temperature) then re-set the ECU so your fuel trims start at zero.

3rd - start the vehicle again and watch the SUM of your fuel trims, Short-term Fuel Trim + Long-term Fuel Trim.

If you see that the SUM of your fuel trims (A/F Trim Mimed. + LTFT) is positive then 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...the entire MAF curve. Try to avoid sudden throttle movements during this process, you want to avoid seeing any corrections based on the Enrichment table settings.

If you see that the SUM of your fuel trims is negative then reduce injector latency until you see the SUM of your fuel trims comes closer to zero. 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, you want to avoid seeing any corrections based on the Tip-in Enrichment table settings.

This is part of a calibration process that should be able to get you close to the ideal settings necessary to properly control your fuel injectors. Please take into account that you will most likely have to fine tune the intake calibration table as the final step. This will be necessary to match the characteristics of these new fuel injectors.

Thanks Tommy, this is what I have been doing. It can be a long process, that why I was looking for any tips.

I wish i could help but Im not aware of any shortcuts.

Sorry for the slow reply here Justnii. Tommy's technique from COBB is the generally accepted technique. It is a slow and frustrating process but there is no real short cut unless you have prior knowledge of the correct settings for a certain injector combination. The closer you can get the fuel trims to zero, the easier your life will be. While the document from CONN touches on this I can't stress enough how important it is to make sure that you don't try swapping injectors and intake at the same time. You MUST either tune the MAF translation table to suit a new intake system with stock injectors, or change the injectors first and tune the scaling/latency with the stock intake. This is an easy mistake to make and can result in a lot of frustration with strange driveability problems.