Power FC 3 Ohms Resistors Sold @ Rx7store.net
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apeiron
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3 Ohms Resistors Sold @ Rx7store.net
Are the resistors sold on Rx7store.net too low of a resistance for the PFC injector drivers? It is my understanding that if the drivers see more than 2 amps, it will fry the circuits?
I have been having issues with ignition break up @ 3000 rpms as well as my wide band showing that the air fuel ratio is off the charts lean 19+ when crusing at any speed above 2000 rpms
This is what is stamped onto the resistors: HEI TMC - 25 3 Ohms 1%
Link is as follows:
http://www.rx7store.net/product_p/in...20resistor.htm
So my question is... could running these resistors with the Bosch 1680 injectors have fried my secondary injector drivers?
I have been having issues with ignition break up @ 3000 rpms as well as my wide band showing that the air fuel ratio is off the charts lean 19+ when crusing at any speed above 2000 rpms
This is what is stamped onto the resistors: HEI TMC - 25 3 Ohms 1%
Link is as follows:
http://www.rx7store.net/product_p/in...20resistor.htm
So my question is... could running these resistors with the Bosch 1680 injectors have fried my secondary injector drivers?
#2
wannaspeed.com
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measure the resistance of your injectors. i think my bosch injectors were 5.1 ohms and i'm running 4 ohm resistors cause thats what i had, but 3 ohm should be fine if your injectors measure out the same as mine. the way to do the math is:
battery voltage / inj ohm + resistor ohm = AMPS
SO
12-14 volts / 5.1 +3ohms = 1.48 - 1.73
So even at peak battery voltage the 3ohm injectors are plenty safe with 5.1 ohm injectors.
Some brand injectors are around 2 ohm though which would put it at 2.8 amps with 3ohm resistors.
battery voltage / inj ohm + resistor ohm = AMPS
SO
12-14 volts / 5.1 +3ohms = 1.48 - 1.73
So even at peak battery voltage the 3ohm injectors are plenty safe with 5.1 ohm injectors.
Some brand injectors are around 2 ohm though which would put it at 2.8 amps with 3ohm resistors.
#4
Eye In The Sky
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There have been discussions on how much power the PFC injector drivers can safely handle. Some say the low impedance Bosch injectors don't need resistors. Some say they do; 3 or 5 or 10 ohms. I need to go back and reread it.
I was reading pages 80 and 81 of the Datalogit manual. It states that the PFC injector driver's IC contains 4 FETS (field-affect transistors). Each has an impedance of .25 ohms, and that the IC has a total power dissipation safe level of 3 watts. If power is not accumulative, then it will be .75 watts per driver/FET.
Let's do some calculations. I will use a voltage of 14.3 VDC as that is the highest I have seen on any FD. The stock injectors are listed as 13.8 ohms. My Bosch 1600/1680 with the light gray top are 5.1 ohms.
Stock injectors first:
(14.3 / 13.8) * 4 * .25 = 1.04 watts. 1.04 / 4 = .26 The total wattage of 1.04 is way less than 3 watts, and the individual wattage of .26 is way less than .75.
Stock leading and Bosch 1600 secondaries with 3 ohm resistors:
(14.3 / 13.8) * 2 * .25 = .52 watts
(14.3 / 8.1) * 2 * .25 = .88 watts
Total wattage = 1.4 watts. Less than 1/2 of the 3 watt maximum.
Secondary individual wattage = .44 is less than the individual max of .75 watts.
We are safe by both total and individual wattage.
If we do not use the resistors:
(14.3 / 13.8) * 2 * .25 = .52 watts
(14.3 / 5.1) * 2 * .25 = 1.40 watts
The 1.92 watts total is safely less than 3 watts.
The .7 watts per secondary is close to the max of .75.
I would not use this combination as the individual wattage is too close unless it can be verified that total wattage is the main factor.
BUT; if we use 1 ohm resistors we have 1.69 total or .59 per 1600 individual.
1.69 total is less than 3 and .59 is less than .75.
2 or 1 ohms should be safe and give better response than 3 ohms.
Or just get the FJO driver and have safety and more flow.
I was reading pages 80 and 81 of the Datalogit manual. It states that the PFC injector driver's IC contains 4 FETS (field-affect transistors). Each has an impedance of .25 ohms, and that the IC has a total power dissipation safe level of 3 watts. If power is not accumulative, then it will be .75 watts per driver/FET.
Let's do some calculations. I will use a voltage of 14.3 VDC as that is the highest I have seen on any FD. The stock injectors are listed as 13.8 ohms. My Bosch 1600/1680 with the light gray top are 5.1 ohms.
Stock injectors first:
(14.3 / 13.8) * 4 * .25 = 1.04 watts. 1.04 / 4 = .26 The total wattage of 1.04 is way less than 3 watts, and the individual wattage of .26 is way less than .75.
Stock leading and Bosch 1600 secondaries with 3 ohm resistors:
(14.3 / 13.8) * 2 * .25 = .52 watts
(14.3 / 8.1) * 2 * .25 = .88 watts
Total wattage = 1.4 watts. Less than 1/2 of the 3 watt maximum.
Secondary individual wattage = .44 is less than the individual max of .75 watts.
We are safe by both total and individual wattage.
If we do not use the resistors:
(14.3 / 13.8) * 2 * .25 = .52 watts
(14.3 / 5.1) * 2 * .25 = 1.40 watts
The 1.92 watts total is safely less than 3 watts.
The .7 watts per secondary is close to the max of .75.
I would not use this combination as the individual wattage is too close unless it can be verified that total wattage is the main factor.
BUT; if we use 1 ohm resistors we have 1.69 total or .59 per 1600 individual.
1.69 total is less than 3 and .59 is less than .75.
2 or 1 ohms should be safe and give better response than 3 ohms.
Or just get the FJO driver and have safety and more flow.
#7
wannaspeed.com
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I understand. Because they open sooner they will flow more fuel during a given cycle which lowers the overall duty cycle. So there isn't a huge benefit to lower resistance unless your running out of fuel due to high duty cycles. I suppose the fuel maps will have less of a hump during transition as well.
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#8
Need more sleep
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I understand. Because they open sooner they will flow more fuel during a given cycle which lowers the overall duty cycle. So there isn't a huge benefit to lower resistance unless your running out of fuel due to high duty cycles. I suppose the fuel maps will have less of a hump during transition as well.
Since we can tune the transition there is no issue with transition regardless of which resistor or injector driver we use on the bosch injectors.
#10
Eye In The Sky
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The only transistion problem is caused by the PFC's very bad stock transistion values for % DC and initial ms. I have posted about this crap before when I first logged it and showed how to overcome it.
My tuning notes package shows how to best correct it.
My tuning notes package shows how to best correct it.
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