I just want to know what size resistors you guys are running on your 1600cc secondary injectors if your using the Power FC

i have been running 3 ohm resistors and i believe i have fried the driver in the ecu.
The shop that sold me this setup swears up and down that i should be fine with this setup claiming that there are several cars doing the same without issues.
Any thoughts on this?

 

Forget the resistors and get yourself a driver box. FJO and AEM both make good boxes. You'll get much better results than using the resistors.

 

On my factory 87 resistor pack (84-87 fuel injected Rx-7's had an OEM resistor pack with low impedence injectors) they are I think 6 ohm. With 720/1680, I have secondary lag of .35 in the front and .45 in the rear (rear rotor tends to run leaner, this slightly richens it up). Then you can try Pri/Sec transition of 30% with .100 ms and 4-3-2 overlap.

I did notice hesitations on 10 ohm resistors on a different setup, but that was also on a stock 2nd gen ECU. You can also give the FJO box a try. Stay away from AEM, I've had bad luck with their electronics (poor build quality and ******* tech support).

 

Use the FJO driver, it works great.

If you are going to use resistors, you have to first measure the resitance of the injectors. Then choose a resistor that when placed inline with the injector will limit current to or less than 1.5 amps.

R1 + R2 = R3

E = IR; 14.1 VDC = amps * R3, go from there.

Also Watts = IE, for the minimum heat size of the needed resistors.

 

thx for the info guys, i will look into an fjo driver. But no one is answering the question: What size resistors are you using with your 1600s and power fc?

 

The answer is to do it properly you forget the resistor and use a driver box. If you want to use the band aid approach Chuck explained how to determine what resistor you will need. Read this thread and you'll learn everything you need to know and why we're all recommending the driver box over the resistor.

https://www.rx7club.com/showthread.p...ector+resistor

 

Did you not read my post? 6 ohm, they just happen to be factory resistors built into the harness.

 

^^ Sorry i missed that Arghx, is that on an FC though?

thx for the link C Ludwig, i had previously checked out that thread, i am leaning towards the Fjo.

The reason i want to know what guys are using for resistors is because i believe i have fried my secondary injector driver in the power fc, due to using 3 ohm resistors, but the shop supplying me with the resistors is not taking any responsibilty claiming they use the 3 ohm on several other cars without issues.

 

3 ohm is pretty low.

 

^^well thats what i have determined from the researching i have been doing on the topic. The shop that supplied the injectors and resistors gets them from rotary performance (rx7.com) so u think they would work just fine with no ill effects. The shop owner also brought Steve Kans' name into his explanation for these resistors being adequate, sayin he did the math to determine the 3 ohm resistors.
is it possible that maybe i am have another issue, maybe a short in my wiring harness?
i have posted the Symptoms of my problem in the Power Fc forum, heres a link to it:
https://www.rx7club.com/power-fc-forum-47/power-fc-crapped-out-repairable-760659/

 

i use 10 ohm 10 watt resistors.... although after reading that other thread with your issue, i can relate. I can't boost past 7psi without serious breakup. i have checked EVERYTHING but the PFC. i have run new wires to my ignition (PFC to igniter and igniter to coils), new plugs, new wires, coils are brand new, had my injectors flow checked and cleaned, the works... BUT i had a short in my harness when i rebuilt my car which led me to rewiring and removing parts of the harness. The only reason i haven't checked my PFC is because both of my tuners keep telling me it's ok. wish i had a spare PFC kickin around

 

Hey RotaryBred, it seems are paths cross once again.
i found this thread that supports the idea of using a 3ohm resistor with 1600s
so much conflicting info on the forum sometimes.
https://www.rx7club.com/showthread.p...osch+injectors

 

Assuming the PFC can sink up to 2.0A and also assuming your injector measures similarly as what is quoted in that thread (2.8 ohm is mentioned, lower ohm readings have been measured) then that injector and a 3 ohm resistor have the ability to pull over 2.0A at a more realistic voltage of 13.8V. At that voltage a 4 ohm resistor will produce right at 2.0A load. It would be wise in this example to use a minimum of a 5 ohm resistor IMO.

 

ok, so i found this video on youtube to figure out my injectors impedance:

http://www.youtube.com/watch?v=xoh-_6tVjsw


by following these instructions i found my injectors to be 4.4ohms(a high resistance injector?), my resistors are 3 ohm as stated before. Am i overdriving my power fc circuits? i need help pluging my numbers into the formula, but i think it goes like this
14,4v/7.4ohms= 1.87amps
which should be safe? did i do this right?
i'm trying really hard to learn this ****

 

Myself and other notable members from this forum haven't used resistors with 1600 cc secondaries in PowerFC's for YEARS with no ill effects. THERE IS NO NEED TO USE RESISTORS WITH 1600 cc SECONDARY INJECTORS WITH A POWER FC! In fact, 1600 cc secondaries actually perform better without resistors inline because they will receive all of the amperage from the injector driver instead of it being diluted with a resistor being placed inline between the injector driver and the injector. 1600 cc injectors are usually rated at 4.4-4.5 ohms, this is within the range of a high resistance injector. Injector resistance grows the higher the duty cycle rises which will make it less prone to damaging the injector driver under load. If you're unsure of this, check your 1600 cc injectors with an ohm meter to make sure the resistance is between 4.4-4.5 ohms, if so just wire them up normally with no resistor inline, you'll notice not as much injector lag and improved stability without them.

ON A SIDE NOTE: You will gain injector performance with the FJO peak and hold injector driver in this type of application BUT it's not needed if you don't use the resistors as described.

 

damn just checked my numbers
it should be 14.4v/7.4ohms =1.95 amps

 

very interesting, my injectors do fall in the 4.4-4.5 ohms u speak of and your explanation makes perfect sense to me. I am starting to think my issues are not being caused by the Power fc. Why are there so many varying opinions on this?

 

FWIW I'm pretty sure RX7store ships out their fuel kits with 3 ohm resistors.

 

5ohm resisitors 2 years no issues, yes tuning requires some patience to get past some of the stumbles and what not but it works and is safe.

You can you run without. I have seen several guys do this, and I have also seen 2 friends fry their PFC's this way. but have yet to see anybody fry them while using resistors

If my car was not already finished and running fine I would probably opt for the FJO driver though.

Kenn

 

Most stumbling has to due with the rest of the injector setup on Settings 5 if using a PFC/DL. My testing has shown that the previous theory of how to change both transitional fields was wrong. Search on the PFC forum to see if my explanation is still there.

I do not give it out anymore as it is now part of my PFC/DL tuning package.

 

So where is the cheapest place to get an FJO injector driver?

 

^^you can go to the fjo website and find a list of the dealers

is there any way to test the circuits in the power fc to ensure that the injector drivers are still working? or do i have to send the unit back to Apexi?

 

Hey Kenn Chan thx for the reply, what symtoms did your buddies that fried their drivers experience?

 

horsepower freaks has the injector drivers

 

I was hoping other people would have already done the leg work so I wouldn't have to go through each distributors website to see if any of them sell them for cheaper than the $150 I've been seeing most commonly . I'll check HPF though.