hello everyone, i have a set of 41 lb ford injectors which is perfect for the hp goals but the only problem is that they are low impedance and i have high imp drivers in the pcm, its a 95. really thinkin about the resistor box modification but notec told me to stay away from the mod all together but i have read that a few people have had no problems with it, and its hard to find a cheap set of 440 high impedance injectors too, let me know what your guys think.
jason
Im running a resistor box out of an accord i found at a junk yard..... I run low imp. 780cc injectors and no issues...at all!!!. Its cheep...easy and it works.
491whp, 393wtq
11.93@ 127mph
Raven Autosports (902)850-3330
could you reply with a wiring schematic please so i get it right can't be that hard to do but i just want to make sure i wire it right, what are you using for tuning?
thanks
jason
I'm also running low imp. injectors (770cc) but I wired in resistors instead of doing a box. I've never had any problems from the day I did this.
President/Founder - 607 Motorsports
what rating resistors did you use??
better than a bulky resistor box i guess right?
thanks
jason
honda resister box as well with 1000cc injectors wiring is pretty easy
R.I.P. Brian Klocke, you will never be forgotten
u know, you're running pretty small injectors why not just get high impedance..?
you think 41lb injectors are small for 6 lbs of boost? i have 67lb lotus injectors but was worried that i would not be able to make them idle right, you think that i should go bigger?
jason
the only reason running a resistor box to accomadate low imp injectors with a high imp driver is that opening time will be slightly delayed. this means that if your idle quality requires a total pulse width time just above the opening time, you could push into that area and lose control of the injector. it would be take longer for the injector to open than the ECU calculated , and since idleing with extremely small open times is critical to stability, your idle may suffer. Or, it may be just fine with your system. if you have no way to check what your idle open time is, then i say try it. if it works, then pat yourself on the back and call it good. if it doesnt idle properly, you may need to take a different route.
other than that issue, there should be no other concern with running in the higher RPM's. so long as your resistors are properly sized. since you have four injectors, you should place four seperate resistors inline with the grounding signal coming from the ECU. This will allow you to use four smaller power wattage rating resistors, rather than one large wattage resistor if you put it on the supply side. its also important because if your ecu had a problem with the cam angle sensor, it would revert back to batch fire mode, and then fire two injectors at the same time. if you had a properly sized resistor in the supply side for firing in SFI mode, then it would only be half the value needed when firing in MPFI mode. so, just do four total, one on each wire coming from the ECU.
to size them, you will need to know the Ohms value of your stock injectors. then subtract the value of your new injectors from your stock injectors. the answer will be the value resistor you need inline, this will trick the ECU into thinking the same load is still out there. you can fudge the value a little if you cant find the exact value you need...but error on the high side so as to not overload the drivers. Try to go with about a 20W sized resistor for each.
M90'd Built LGO-15 PSI
http://webstarts.com/quadper4mance
just a little FYI about why there are two different style injectors...
A high IMP injector is cheaper by nature, and easy to drive with cheap simple circuitry. but it has its limitations. - slow open time
the reason some cars and high performance engines use a low imp injector is they have circuitry that will slam a huge amount of power to the coil for a very breif period of time, this really gets the injector to open fast. then it will scale back the power to just hold it open for the remainder of the event. This is why they are refered to as Peak & Hold injectors.
a high imp injector may have an opening time of about .2 milliseconds. a low imp injectors typically take that down to about .1 milliseconds, half the time. this is important, becuase if you are using an obscenly large injector so you have massive top end power, it would need a shorter opening time to be able to administer a very small portion of fuel through that huge orfice to control idle. see ? its brilliant
M90'd Built LGO-15 PSI
http://webstarts.com/quadper4mance
but by using a resistor box, you would be negating that shorter opening time that the low imp could do, it will most likely still open just as slow as a high imp injector if feed by resistors, and not by a PWM injector driver to slam it open.
M90'd Built LGO-15 PSI
http://webstarts.com/quadper4mance
triple post FTW j/k
That was very informative I have always wondered what the difference was.
Also keep in mind that low impy injectors date waaay back to a time when analog circuitry controlled EFI and current controls rather than voltage controls were state of the art. Even as controllers progressed, sequential efi was still a long way off for most applications so injectors were fired in batches, meaning an injector fired multiple times for one intake event. It was more likely that an injector would become "too big" to idle if the desired pulse time for fuel had to be cut in half, quarters, or even eighths to maintain the minimum fuel needed. It still seems strange to me, today, to hear of 50 and 60# injectors in a 4 cyl, yet modern lightweight injectors combined with sequential injection make is much easier to dial in a small pw without overfueling.
I would still tend to stay away from adding resistors. I'd likely try to find an appropriately sized set of Multec2 or Weber Marelli Pico injectors due to those injector's faster response times. YMMV.
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