PWM on Low-Z injectors with resistors?

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spitnl
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PWM on Low-Z injectors with resistors?

Post by spitnl »

Hi guys,

I am converting a Rover SD1 vitesse to MS2 v3.0
Al going well but I am running into a problem I haven't been able to find a definitive answer for.
My question is do I need to use PWM for the injectors(original) or not?

The injectors are 2.5Ohm each, the power pack resistors are 6.5Ohm each.
If I do the calculations:
4 injectors per channel so
4x9Ohm parallel equals 2.25Ohm per channel
13.4V/2.25Ohm=5.95A
The manual says 14A max per channel so I should be OK?

Fred
racingmini_mtl
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Re: PWM on Low-Z injectors with resistors?

Post by racingmini_mtl »

spitnl wrote:My question is do I need to use PWM for the injectors(original) or not?
No
spitnl wrote:... so I should be OK?
Yes

Jean
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spitnl
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Re: PWM on Low-Z injectors with resistors?

Post by spitnl »

Great!
Thanks for the quick reply, Jean.

Fred
DaveEFI
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Re: PWM on Low-Z injectors with resistors?

Post by DaveEFI »

I have an SD1 - but an EFI - and binned the resistors. As just one more set of connectors to give problems. Had zero problems setting up and using PWM. The V3 board was designed for driving Lo-Z injectors directly.
Rover SD1 3.5 EFI
MS2 V3
EDIS
Tech Edge O2
London UK.
spitnl
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Re: PWM on Low-Z injectors with resistors?

Post by spitnl »

Hi Dave,

Thanks for the reply.
I know I can bin the resistors, but I'd like to at least keep the looks original.
Haven't had problems with the resistor pack so far.

Did you notice a difference in how the engine runs when going PWM?
Spiffy
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Re: PWM on Low-Z injectors with resistors?

Post by Spiffy »

You can either scrap the resistors and run pwm, or keep the resistors and run them as high imp. injectors.

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DaveEFI
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Re: PWM on Low-Z injectors with resistors?

Post by DaveEFI »

spitnl wrote:Hi Dave,

Thanks for the reply.
I know I can bin the resistors, but I'd like to at least keep the looks original.
Haven't had problems with the resistor pack so far.

Did you notice a difference in how the engine runs when going PWM?
On first reading up about MS many years ago, the point was made that driving injectors PWM rather than use a resistor was a better way, and that agreed with my basic electronics knowledge too - to control any 'motor' you need as low impedance a source as possible. Basically, add a resistor and you slow down the response speed. So I decided on that from the off. So I never tried MS using the resistors.
The big difference changing from the flapper to MS was actually at the lower rev band of the engine. It now pulls like a train from just above idle. Just how much this is down to the injector control, I dunno. As the flapper tends to run rather weak other than at WOT/high revs. Or rather some do.
If you want to keep it looking original, are you keeping the flapper AFM? I've replaced that with a plain tube, with a ATS in it.
Other thing is the engine wiring loom on a Vitesse is generally in poor condition by now - cracked insulation, etc. Broken injector connectors. And you no longer need the cold start injector and control. So if making up a new loom, better to keep it as simple as possible.

If you'd like my external wiring diagram for my EFI with MS, PM me with your email address and I'll send it to you as a PDF.
Rover SD1 3.5 EFI
MS2 V3
EDIS
Tech Edge O2
London UK.
spitnl
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Re: PWM on Low-Z injectors with resistors?

Post by spitnl »

You are correct, of course, running loosing the resistor pack would be better.
I read on the forum here about a dead time of 6ms!
I'm going to test the injectors, if the dead time is indeed that high. I may still convert PWM.

The plan with this car to keep it as original as possible and be able to swap back to the original 4CU.
So I have mounted the MS2 in a gutted 4CU housing and using all the original wiring, sensors etc.
Not using the cold start injector and flapper AFM, but they are still mounted.
Ignition wise, I did make a concession and fitted EDIS8 with coils., so I no having to phase the distributor and being able to keep it at the correct firing angle.

You may be wondering why I am converting to MS2, when I am keeping all the original stuff.
Well two reasons, one; the car was hard to start and felt like it was holding back when driving, two; I am hoping to gain some experience before starting a more challenging turbo project.

Thanks for the tip on the wiring. I haven't found any broken connectors or brittle and cracked insulation yet.
Guess I'm lucky there.

Thanks for the offer on the wiring diagram, I'll pm my email address.
I am starting with the base map as recommended, but If you have got an msq to check against I'd really appreciate it.

Fred
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