low imped injectors, does pwm always has to be 100% and 25,

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buncey
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low imped injectors, does pwm always has to be 100% and 25,

Post by buncey »

low impedence injectors, does pwm always has to bee 100% and 25,5 ms?


just curous as im useing bosch 803 low inpedence injectors with 10r ohm resistors in paralel.

just wondering whever the pwn should it always be at 100 and 25,4? with these resistors in line?
Navi
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Post by Navi »

according to the manual, you need to tune these values, see:

http://www.megamanual.com/v22manual/mtune.htm#pwm

or you can damage/overheat your injectors
buncey
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Post by buncey »

so if im running 10r resistors in paralell on injectors, am i right in think i need

PWM Time Threshold to 25.4 msec,

and the

PWM Current Limit 100% ?

is that currect ?

as currently its set at PWM Time Threshold to 25.5 msec, / PWM Current Limit 75% ?
RNash
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Post by RNash »

Yes,
You treat low impedance injectors with resistors in series (NOT Parallel) the same as high impedance injectors.
Below is a cut from the manual at http://www.megamanual.com/v22manual/minj.htm#injresist

--------------------------------
Injector Resistors

However, instead of the flyback board, you may choose to use resistors in series with your injectors.

Several people reported that resistors do NOT result in significantly longer opening times, or any other troublesome effects, so this is a good solution for many installs. To eliminate PWM altogether, use a 5 to 8 ohm resistor (with a 20 to 25 watt rating) in series with each injector.

If you want to avoid using PWM with your low-impedance injectors, you can use ballast resistors in series with the injectors. You should use one resistor (20-25 Watts) in series with each injector, otherwise the injectors may not all draw the same current, and the failure modes become complicated and difficult to diagnose. As well, you would need a very large resistor to handle more injectors. For example, if you allowed 2 Amps through four 1.2 Ohm injectors wired in parallel (0.3 Ohms total) to one 7 Ohm resistor, the power dissipated would be:


P = V * I = 12.5 Volts * 2 amps x 4 injectors = 100 Watts!
If you use resistors that limit injector current to less than 2 amps, you can disable the PWM mode (by setting PWM% to 100%, and time threshold to 25.4msec) and treat the system as high-impedance. To limit the current to under 2 amps, you need:

resistor ohms = (alternator voltage / 2.0 amps) - injector resistance

For example:

resistor ohms = (14.0 volts / 2.0 amps) - 1.2 ohms

=> resistor ohms = 7.0 - 1.2 = 5.8 ohms
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