I\'m going to be installing some new injectors into my FD, however, I\'m a bit confused by the resistor thing.
I\'m going to be using Bosch 1680cc injectors and I\'m sure that Carl has said not to worry with resistors as an Apexi Power FC doesn\'t care and will happily run without them.
However looking on RX7.com they all seem to run resistors or injector drivers like the one at //http:///www.fjoracing.com/products/injdrvr/
I don\'t think I\'ve ever seen anyone in the UK using an FJO or AEM injector driver (maybe I haven\'t looked hard enough). I just find it REALLY confusing.
We have and do run FJO injector controllers and alternatively resistors. I would recommend the FJO for convenience and changing the signal.
You will find much much more knowledge on RX7club than you will with certain tuners.
Indeed, although I\'ve run those Bosch 1680 injectors on my car all year, with a PFC and no resistors and there have been no problems.
And there you have my problem. I know a little about engines and less about electronics, so I guess I will try and explain this how I think it works.
So we know that it is possible to run these injectors without resistors. I\'m guessing this works due to the fact the original injectors are high impedence and the Bosch ones are low (if it were the other way around, I\'m guessing it wouldn\'t work)
Anyway what I suppose is happening is that the ECU is happily putting down a high voltage (?! I dunno is it amps?!) because it thinks the injectors are high impedence. Therefore does it mean that it could possibly cause the injectors to stick open as the injector is getting a higher voltage than it should be? I\'m guessing in the short term this won\'t be a problem, but in the long term (don\'t know how long that is) it could make them fail.
Putting resistors in-line is an attempt to make the injectors look like the old injectors by increasing the impedence.
Which sounds fine, until I read a thread on RX7.com (curse them for complicating things) by saying this also may not be good as the voltage to keep an injector is less than the voltage needed to open it in the first place, and therefore could lead (I think) to over fuelling.
Now the FJO thing seems to get round this using witch-craft that I don\'t understand...and I guess the real thing to do is get an ECU that can handle both low and high impedence injectors out of the box...but then where would you get it mapped.
Please explain to me (in small children\'s language) if my theories are wrong, and the real reasons for doing this.
fjo controller allows better control of low impendznce injectors to proper peak and hold signal, i ran without resistors for years on the apexi not ideal but it worked but i dont have to worry about that anymore now i run motec with 4x1680
I\'m about to install a 4 channel FJO with my new injectors. Felt it was better for controlling the primaries at the lower pulse widths.
Not a bad buy either.
Shaun
Can you give me a review on those 1680 bosch injectors? I might be getting some next year for my FC :) where did everyone get theirs?
kg parts sell them the cheapest
can anyone actually say what resistors they actually use with thier 1600 secondaries?
I never ran resistors btw
I used 10 ohm 25w resistors from RS components - £10 delviered from the pair.
Pip is mapping my car, so I asked him if he would like them fitted or not. his exact words were \'it depends how long you want your ECU to last\'.
I\'d rather not take the gamble, especially with the availability of PFC\'s as it is right now.
The resistors are there to limit current, as the low impedance of the Bosch injectors will cause more current flow. The voltage supply will be what ever your alternator chucks out, and given that the engine will be on higher RPM when the secondaries come on line, voltage should easily be 14V or over.
However, the resistors will act as a voltage divider with the impedance of the injectors (around 3-5 ohms I believe) so the injectors won\'t see the full 14V - this can affect the lag time - effectively giving a delay before fuel is injected - it\'s specified in fractions of 1ms, and for some injectors may be just over 1ms.
The proper Peak/Hold drivers provide full voltage to open the injector, and then a lower holding current (voltage reduced) to keep them open. This prevents the injectors from overheating when they are driving at high duty cycles.
The Apexi Power FC has probably got current limiting circuit built in to protect it\'s output transistors and hence why no need to use resistors - but I would imagine the injector drive would be better if using a proper peak/hold driver circuit.
In any case, it would be easy enough to map out the differences the lag time changes cause by just altering the duty accordingly.
Prof superb explaination
Ok so what resistor is adequate for kg 1600s with a pfc. Has anyone tried anything other than 10 ohms
wow, this has turned into a very good informative thread.
I always thought for was was probably about £120 and a little bit of time the risk wasn\'t worth it. Especially having 4 peak and hold injectors.
Blitz - How do you find the tick over running on 4 1600\'s ?? Although the Motec is designed to run Peak and hold injectors compared to a PFC. Thinking about the white top ones for an LPG setup in the FB.
Shaun
my porting is massive so idle at 1700 rpm on 4X1680cc, really depends on ports, but motec controls them well
Quote from: DR SCHNITZEL;587944Ok so what resistor is adequate for kg 1600s with a pfc. Has anyone tried anything other than 10 ohms
Going by the current flow through a high impedance injector - which is a little over 1 Amp, you could probably use a resistor in the range 6-10 ohm\'s - go lower than 6 and the injectors could overheat, go much higher than 10 and you may not get the injector firing properly. Wattage should be 10-15.
perfect cheers