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Tuning larger injectors

Practical Diesel Tuning

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Hi,

I have asked this question before but i think i misunderstood the concept and now im just confused.

when we say larger injector we mean same volume for shorter pulsewidth? Or does larger nozzle increase the total volume of the injector?

Also does that mean the rescaling of the injector pulse width table is mainly to adjust for the latency/deadtime of the injectors rather than size/volume? At least when talking about the idle part and Assuming we dont have the injector data to properly calibrate volume vs pw vs fuel pressure

another thing if i decrease the injector pulse width value in the table or increase the Y-axis which is volume does that tell the ecu to retard the timing and decrease the pilot injection and so on? Is that the correct way of doing it?

or do i need to go to individual tables and adjust timing, fuel pressure and pilot injection?

if im understanding correctly larger injector need more timing at idle to reduce smoke and less everywhere else to reduce cylinder pressure?

Also larger injectors need more pressure everywhere to compensate for latency?

Im not sure what i would need to do with Pilot injection? Do i leave it as is since im making general adjustment with the injector pulse width table?

for injector pulse width i should only decrease it by 10-20% especially in the areas where it smokes? I believe i dont need to cut the values in half for 100% oversized injector?

Fahad, I'll do my best to answer your questions below:

when we say larger injector we mean same volume for shorter pulsewidth? Or does larger nozzle increase the total volume of the injector? When we say larger injector we typically mean a nozzle size larger than stock, in the simplest terms the injector will flow (stock * (1+.01x)) amount of fuel, where 'x' is the percent-over advertised by the injector manufacturer.

Also does that mean the rescaling of the injector pulse width table is mainly to adjust for the latency/deadtime of the injectors rather than size/volume?

Adjusting the pulsewidth table is typically done for size/volume of calculations. Latency, and deadtime will of-course play into total pulsewidth req'd to achieve a fuel volume but I wouldn't get hung up on it.

At least when talking about the idle part and Assuming we don't have the injector data to properly calibrate volume vs pw vs fuel pressure.

I typically only rescale the lower parts of the pulsewidth map near idle if I have injector data or if I'm having trouble with idle quality. The injectors rarely flow at their advertised rate over stock at short pulsewidths/low pressure.

another thing if i decrease the injector pulse width value in the table or increase the Y-axis which is volume does that tell the ecu to retard the timing and decrease the pilot injection and so on? Is that the correct way of doing it?

Your intention in manipulating the data in this table is to make it as accurate as possible so that the ECU can precisely meter fuel into the engine. Only once that is done should the timing, fuel pressure, etc. tables be adjusted to maximize combustion efficiency/NVH.

or do i need to go to individual tables and adjust timing, fuel pressure and pilot injection? This is preferred.

if im understanding correctly larger injector need more timing at idle to reduce smoke and less everywhere else to reduce cylinder pressure? The larger injector will generally need more timing anywhere it's latency/deadband is longer than stock and less as fuel pressure and boost come up (high load).

Also larger injectors need more pressure everywhere to compensate for latency?

This usually helps, but depends on injector architecture/design. Let your ear and eyes be your guide. Add pressure until NVH becomes noticeable and your smoke reduction plateaus.

Im not sure what i would need to do with Pilot injection? Do i leave it as is since im making general adjustment with the injector pulse width table?

On larger injectors it may help to adjust the pilot pulsewidth table if one exists and you have data from the injector supplier about short pulse behavior. Anecdotally I'll tell you that adding mm3 to pilot demand may be needed to get the pilot shot up to it's 'stock injector' level.

for injector pulse width i should only decrease it by 10-20% especially in the areas where it smokes? I believe i dont need to cut the values in half for 100% oversized injector?

If your pulsewidth table is done right, you should be able to control smoke with your mixture limit tables fairly easily. Your minimum lambda in the table should match your sensor (or eyeball) data in the tailpipe. The responses above will hopefully offer some clarity on this question.

-Nick

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