Injector resistance

[Q45tech]

Acceptable range of resistance is always in dispute.....................but the exact same diameter wire with the exact same number of turns in a solenoid should be exactly the same within say 1%

A 12 ohm injector should read 12 ohms +- 0.12 ohms.

However differences in exact local injector temperature will change the resistance of copper by increasing it as the temperature increases.

The reason the oem FSM lists 10-14 ohms to to consider warranty and the usual inaccuracy of technicans ohmeters.

The ecu measures the applied voltage [batterry voltage] and adjusts the open duration to compensate as the voltage drops below [or rises above]13.2 volts.

If an injector is not 12 ohms the ecu does not know it and still applies identical voltage corrects to all injectors.

So if 1 volt is significant so is 1 ohm

The injector lift point and time to flow vs volume will vary as the voltage or resistance varies.

It is so important that the ecu compensate for battery voltage that a separate map is provided to adjust the injector open time this is also corrected by the coolant temperature [assuring that some knowledge of the approximate injector body temperature is included in the open trim.

"a command signal whose duration is indicative of the amount of fuel to be injected. The command signal is determined based upon a measured throttle position, engine speed and engine load. A resistance of a solenoid coil of the electromechanical mechanism is then calculated and the command signal is adjusted by incrementing or decrementing the command signal to compensate for variations in the measured resistance of the solenoid coil of electromechanical mechanism due to temperature variations. " .........http://www.freepatentsonline.com/6148800.html

"a typical electronic injector takes 1 - 1.25 ms to fully openand some non-zero (around 0.5 ms) time to close."

Anyway I invite readers to study Ampere's Laws to determine how even a 1.0 ohm difference can materally affect the AF ratio of a single cylinder

http://eshop.engineering.uiowa...2.pdf

[Q45tech]

http://www.diy-efi.org/efi332/...h.htm

I have found 0.2 milliseconds per volt [from 13.2 volts as read by ecu] as a function in some equations.

"Battery Voltage Correction (ms/V) (BatFac) is the number of milliseconds that MegaSquirt-II (or MicroSquirt) adds to each fuel injection pulse to compensate for the slower opening of the injectors with lower supply voltages. Generally 0.10 ms/V or 0.2 ms/V is about right. "

Pretty significant at idle or cruise [1.2-2.0 msecs] not so at WOT [11-9.5 msecs].

One might look at a Power Balance test to see if any correlation between injector resistance and flow= rpm drops.

good readinghttp://www.megamanual.com/ms2/configure.htm

[Q45tech]

Hope I'm being clear that an injector that is not 12.8 ohms [corrected for ambient temperature and 1% manufacturing tolerance] probably doesn't flow the same fuel as one which reads the average of all the good injectors.

This will probably show up as an unbalanced idle and cruise [how ever at cruise the O2 system can probably correct to some degree]............may not be material in acceleration depending on how much the flow difference is.