Ms3x and low z injectors

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jasaircraft
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Ms3x and low z injectors

Post by jasaircraft »

Is it ok to drive 4 low z injectors sequentially? Batched? (Stock evo 560cc ones)
Will they perform as good as with the resistor box? Edit: they must use resistor box if they are the X board's injector outputs.
DaveEFI
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Re: Ms3x and low z injectors

Post by DaveEFI »

In theory, using resistors is not a good way of driving injectors. But what the differences are to performance in practice, I dunno. Given the costs of this project, I'd add a peak and hold board, if that is easier than changing the injectors to Hi-Z types.
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jsmcortina
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Re: Ms3x and low z injectors

Post by jsmcortina »

A number of years ago, I tested using injectors with resistors as described in the manual and they ran fine.

James
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billr
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Re: Ms3x and low z injectors

Post by billr »

How did the dead-time and voltage compensation compare between using P & H and resistors?
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Re: Ms3x and low z injectors

Post by jsmcortina »

I don't recall the exact numbers, but the deadtime was "about normal". I don't have a standalone P&H to compare to.

James
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racingmini_mtl
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Re: Ms3x and low z injectors

Post by racingmini_mtl »

Inline resistors will slow down the injector opening time because the full battery voltage is not applied to the injector and it will slow down the injector closing time because there is more current flowing through the injector than in the hold phase of a p&h driver. How large are these differences? I don't know and they likely depend on the injector, the resistance value and the driver used. The combined effect of both opening and closing times can also explain why the dead time still looks "about normal".

But that means it becomes more difficult to precisely control very short pulse widths. So if you need a very large dynamic range, a peak&hold driver will make a difference. Moreover, you will have better control over a wider range of battery voltage if you use a current sensing peak&hold driver. This may make starting more consistent under extreme conditions.

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jasaircraft
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Re: Ms3x and low z injectors

Post by jasaircraft »

Thanks for the answers guys. Im running low z evo 560cc ones with the nissan resistor box on my personal ca18, all seems ok i havent corrected the deadtimes yet
DaveEFI
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Re: Ms3x and low z injectors

Post by DaveEFI »

jsmcortina wrote:A number of years ago, I tested using injectors with resistors as described in the manual and they ran fine.

James
Oh indeed. My car has early factory injection that used Lo-Z and resistors. But B&G made a big point of designing the V3 board with drivers and software which could drive them directly. Are you saying that was wasted effort? :D
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billr
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Re: Ms3x and low z injectors

Post by billr »

I think low-Z with proper P & H will always have some advantage. As you suggested towards towards the start of this thread, the question is a matter of cost vs. benefit. Thanks to Jean B. the cost is trivial, so even the possibility of "benefit" is enough to justify the P & H for me. Before that, there were the single-IC solutions like the cherry CS453/454. Too bad something like that isn't still in production.

Speaking of cost, what does a set of those big resistors run? (New, not a steal out of a JY.)
jasaircraft
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Re: Ms3x and low z injectors

Post by jasaircraft »

One thing is for sure, high z injectors cost much more than low z. Checking at Fuel Injector clinic sets.
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Re: Ms3x and low z injectors

Post by vw_chuck »

DaveEFI
What do you mean by this?
"But B&G made a big point of designing the V3 board with drivers and software which could drive them directly"
DaveEFI
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Re: Ms3x and low z injectors

Post by DaveEFI »

vw_chuck wrote:DaveEFI
What do you mean by this?
"But B&G made a big point of designing the V3 board with drivers and software which could drive them directly"
The 2 injector drivers on the V3 board were specifically designed with LoZ injectors in mind - driven PWM with no resistors.

The 8 injector drivers on an MS3x can't drive LoZ injectors directly.
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tecwizrd
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Re: Ms3x and low z injectors

Post by tecwizrd »

DaveEFI wrote: The 2 injector drivers on the V3 board were specifically designed with LoZ injectors in mind - driven PWM with no resistors.

The 8 injector drivers on an MS3x can't drive LoZ injectors directly.
I haven't read through the manual completely yet, but you peaked my interest.

I take what you said to mean:

I will need to run a peak and hold or resistor (my choice) with low impedance injectors or run high impedance injectors, if I want to run sequential injection.

Correct?

Also, will I need a separate peak and hold for each injector to run sequential?
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Re: Ms3x and low z injectors

Post by racingmini_mtl »

tecwizrd wrote:Correct?

Also, will I need a separate peak and hold for each injector to run sequential?
Yes and yes.

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tecwizrd
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Re: Ms3x and low z injectors

Post by tecwizrd »

Thank you.

I followed the link in your sig, I will read through that and the rest of the manual.

Would it be better to post questions in this thread or start a new one?

I want to get my head wrapped around the fuel part of my install before I get it wired in.

The install will be on a 98 4.6L Mustang. No factory wiring or ECU.
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