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Injector Dead Time

EFI Tuning Fundamentals

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I recently had my car tuned on Hondata S300 and the tuner didn’t input the correct injector dead times. Can I simply change this myself or do I need to have the car retuned? Also, the car seems to drive fine. How important is this?

Here's the #s from the actual tune and the documentation that came with the injectors. Not sure how significant the difference is.

Tune with Incorrect Dead Times: 1.69, 1.16, .88, .69, .55

Fuel Injector Clinic Documentation: 2.52, 1.59, 1.15, .89, .72

Attached Files

It'll probably run ok until you have a voltage change. I have dealt with cars where the tuner did the same and didn't take a moment to check into deadtime calibrations and they had the car running fine, until the alternator gave out or degraded etc and then the AFR's chased their tail and the car ran terribly otherwise.

You can do the math to main fuel table around the 14 V cell, but without verifying the change I wouldn't advise doing that. Injector deadtime affects the calculated opening time of the injector, so the error is now baked into the fuel table.

To me this is the kind of thing Andre preaches about all the time in regards to tuner laziness, but perhaps he just forgot or made a legitimate mistake. That said the tuner should correct the tune in my opinion.

Is the HondataS300 a Pulse Width tuned ECU? If so, the difference in the dead times has been baked into the tune as such, so each pulse (presuming the second last values are 14V and the engine is running at 14V) has an extra 0.2ms (0.89ms-0.69ms) of opening time in the injector pulse width value to accommodate this. Whenever the battery voltage moves away from the voltage that the tuning was done at, then the fuel base pulse width will stay the same as this is the table value, and the fuel actual pulse width (Fuel Base Pulse Width + Injector Dead Time) will change.

So at the lowest Voltage in the table, you will have 2.52ms - 1.69ms = 0.83ms in difference in the amount of opening time added to the FBPW to get the FAPW. With these times, the engine will run leaner as the injector takes longer to open and start delivering fuel than has been programmed into the ECU. If you have a FBPW of 1.6ms then you are looking at a calculated FAPW of 1.69 + 1.6 = 3.27ms, This should actually be 2.52 + 1.6 = 4.12ms. The longer dead time will use up injection time (and the injector may not have fully opened by this stage as well) so you end up with only 0.77ms of fuel injected, or 48% of what has been tuned into the ECU.

Injectors can also have strange behaviors in the non linear region of operation, with some that I have tested flowing more fuel at lower injection times than longer, due to the pintle opening, and then "bouncing" and partially closing, before opening again.

Thanks for the replies. I really appreciate it. Unfortunately, I don’t think that the tuner will be willing to redo the entire tune. So I guess my options are to leave it as is or find another tuner to retune the car.

Will this primarily affect part throttle drivability or is it actually able to hurt the engine over time? If it might hurt the engine, then I’ll just have pay to have the tune redone.

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