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fuel injector resistor bypass?

8764 Views 15 Replies 7 Participants Last post by  82MKIILtype
Anybody know how to and how easy it is to run HIGH impedance injectors on a mk2 85 5m-ge. thanks
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it should be pretty easy... just... bypass the resistor pack as you said. hook both wires coming out of the resistor pack to the one wire going into it, and you should be straight. it'd probably be a good idea to use connectors or something so its easily reversible.

actually there's a good chance you'll be ok keeping the resistor pack in there even with the high impedance injectors. nothing bad should happen. it might slightly effect your fueling in that more time will be spent opening the injectors for a given pulse width, but it probably won't be a big deal at all.

Actualy,you can,possibly will,burn out the injector drivers in the ECU if you don't bypass the resistor pack.Local dealer cooked 3 ECU's in a camry,until I started asking questions,and figured out they had a newer engine with the wrong injectors.
you wont burn a 5 or 7m ecu by using high impedance injectors and dont need to bypass the fuel injector resistor. the only way to burn the ecu is if its designed for high impedance injectors and you use low impedence. the extra current draw in this case will fry the injector drivers.
William,why would it have happened to the Camry then? Said car was an 88 which requires 1.7 ohm injectors,had 89+ units in it which are 13.8's.
My reason for asking-I figure the 87-88 ecu is more current electrics than our 5m stuff,if the 5m ecu won't cook,the camry should not have.
i dont know, but i know severla supra owners running high impedance rx7 550's with no problem. one friend has been running them for ovr 2 years. on a supra the injectors are batch fired. they fire in 2 sets of 3. the supr runs ~3-4ohm injectors stock. that is a load of ~1ohm since they are wired in parrallel. 3 13.7 ohm injectors would translate into just a hair over 4ohms total load. that isnt ver much for a supra, but if the camery fires in 2 injector batches it would go from ~2ohms to ~7ohms, or if its direct fire it would go from the normal 3-4 to 13+. i dont see why that would fry the ecu but i gues if it doesnt have enough current to open the injector i guess it could cause problems. i dont see it frying the ecu though.
btw shawn, were they positive the ecus were bad, or were the injectors just not firing? i can see the ecu being good in this case and just not having the current to fire the injectors. which i guess to them prolly looked like a bad ecu. espeacially if they didnt notice the screwup.
also, my guess is the 5m and 7m fuel injector resistor prolly makes each low impedance injector the same as the high impedance, so figure doubling the resistance of the circuit on the camry ecu when the wrong injectors were installed and i bet the injectors wouldnt fire, less injectors(2 per batch instead of 3) = overall higher impedance when wired in parrallel. guess i need to go check the resistance on a 7m fuel injector resistor pack.

p.s. hope all this makes sense, if not ill rewrite it tommarow when im not in so much pain. just finished helping eric fix his car.

what u say is prolly true especially since your friend have been running
hi resistance inj without incident for 2 years but: inj are electrically reistors in series with INDUCTORS so ecu driver electrical stresses can
become a bit more complicated especially since we don't know the ecu driver protection circuitry used. After all is said and done I would accept ytour friends successful use of hi resistance injs successfully as evicdence that hi resistance injs are safe to use.
well, the thing is, ive never seen any kind of amplifier burn up from too much resistance. that just doesnt make sense. the thing is the lower the resistance of a load at a given voltage, the higher the current it will draw. current will take the path of least resistance. in a parralel circuit, current is diveded. since the injectors are in parralel, they share the current(eq, 9ma would equate to 3ma per injector at 12v)also, take an audio amp thats designed to run say 50watts at 4ohms. if you drop the load to 2 ohms, the wattage increases to 75watts. watts = voltage x current so if you increase the resistance to say 8ohms, the power drops to 25watts so if voltage stays the same, current has decreased(estamited. jsut an example). since the camery has to fire less injectors, it makes since it would emit less current. then when you increase the resistance by 100%, it may not have enough current to fire as the current is decreased further. however, the supra ecus fire high impedance injectors fine with the fuel injector resistor in place. simple point i was making was too much resistance isnt gonna fry the injector drivers, but instead make it appear they are non functioning and the ecu's were most likely still good. just appeared to be bad and i can understand the mechanics thinking it was bad if they didnt realize they used the high imp. injectors instead of the required low imp. also, if the camry inj. are indeed ~1ohm as shawn stated, that means they were designed to supply even less current per injector then the supra ecu's. basically, injectors are just solinoids, and it takes current, not voltage, to create the magnetic feild required to open a solinoid. anyhow, this has drifted from the question. the simple answer is no need to bypass the fuel injector resistor on any mkii or mkiii in order to use high impedance injectors.
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williamb82 said:
btw shawn, were they positive the ecus were bad, or were the injectors just not firing? i can see the ecu being good in this case and just not having the current to fire the injectors. which i guess to them prolly looked like a bad ecu. espeacially if they didnt notice the screwup.
Took apart ECU's,injector drivers were cooked on all 3,very visible. :shock: Even changed the engine harness once.After those 4 parts,the tech that got it last,called me and asked WTF.Toyota tech line had no clue either,car was in the dealer for 6 weeks.I happened to have a core with the correct injectors,plugged them and another ECU in and all is well.I just happened to have my injector cheat sheet with me that day,and we gave it a try.Maybe we were just lucky.
well, i dont know why they would have burned out like that. guess the camry ecu is alot different. i know that high impedance injectors will work in 7ms though for a fact. strange thing with the camry. wish i could get ahold of a diagram for the ecu, and one for the 5 and 7m ecu's. then i could see whats so different in the injector drivers.
The keyword here is "Impedance" which can throw a wrench into the common terms and formulas that are normally associated directly with DC (Direct Current) circuitry since Impedance is generally a term associated only with AC (Alternating Current) circuitry. The combining of electrical resistance and the impedance characteristics of an electromagnetic coil in a fuel injector circuit complicates things a bit to the point where the issue is not strictly based on DC voltage and DC current flow alone. I will try and explain more on this tomorrow. Stan is on the right track in that the terms "Reactance" and "Inductance" coincide with a circuit that has impedance values. IE: Z= R+IX where Z is Impedance and X is Reactance. Fun-fun-fun!

William, remember that a loudspeaker is not a DC device but an AC device and thus has an impedance value rather than a direct resistance value.
Okay, lets see if I can make some sense out of what is taking place here in respect to damaged ECU's as a result of using the wrong impedance injectors. :D First off, the 5MGE ECU has only one power transistor that is used to fire all 6 injectors at one time. The injectors on the 5MGE are configured in 2 banks of 3 injectors with each bank of 3 wired in parallel and each parallel bank is connected to a series 2 ohm current limiting resistor inside the solenoid resistor pack. Lets assume that all 6 injectors have a 2 ohm impedance value. 2 ohms divided by 3 = .66 ohms per bank. Add in the 2 ohm series current limiting resistor and you end up with a total of 2.66 ohms resistance per bank. Now, connect both banks together to a common ground point and you now have a total of 5.32 ohms of resistance. Using Ohms Law, E divided by R (12 volts divided by 5.32 ohms) = 2.25 amps of DC current that will theorectically flow through the power transistor in the ECU when the transistor is biased On (turned On) by the ECU electronics. Swap the injectors for high impedance 12 ohm injectors and the DC current drops to 1.0 amps with the current limiting resistor pack still in the circuit.
In the case of the Camry, my 89 electrical diagram for the 3SFE engine shows that all 4 injectors are fired together at the same time, just like the 6 injectors on the 5MGE. But, the 89 diagram doesn't show a current limiting resistor pack anywhere in the injector circuit. :wink: The specs. for the 89 injector solenoids indicate 13.8 ohms for each injector (high impedance type). 13.8 divided by 4 = 3.45 ohms. 12 volts divided by 3.45 ohms = 3.47 amps. That's a fair amount of current flowing through the driver transistor in the 3SFE ECU.
Now for the tricky stuff. The current limiting resistor pack not only helps limit the amount of total DC current that is allowed to flow through the injector circuitry, but also helps to cancel out any peaks or spikes in the DC current that can occur when an electromagnetic field and electromagnetic inductance is created by energizing the solenoid windings in the injectors all at the same time. Any spikes in DC current could possibly damage the driver transistor in the ECU. So, my guess is that the high impedance injectors were a mismatch for the 88 Camry ECU and somehow caused the DC current flow to become unstable and damage the injector driver transistor. Williams' theory may be right in that the high impedance solenoid windings placed too much resistance in the injector circuit with the current limiting resistor pack still in place on the 88 Camry, thus causing unstable operation of the solenoids and erratic flow of DC current through the injector driver transistor.
:roll: Whew!! Sorry for this very long winded thread!! Please correct me on anything that I may have wrong on this subject or if I have overlooked something!!

Time for me to take 2 Tylenol and call it a night! 8)
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OTOH, you could always swap the resistor pack for a flux capacitor and eliminate the problem. :lol: Just kidding!!
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