Fuel Injector Resistance ?

[NigelS]

My car is an ISUZU Piazza (Impulse) XE, DOHC Two litre,1981.
I have leaking fuel injectors, there very old! Can I change the injectors for units of different resistance? What damage could result? The injectors as standard are,230cc/min flowrate,have 3ohms resistance with 7ohm dropping resistors.And have the short length of fuel tube attached permenantly,I've made a suitable fuel rail to enable the more usual "O"ring seal injectors to be used, if I can find replacements.I have a set of injectors of 16 ohms resistance,could these be used?? Kind regards Nigel-S.

 

[Retracnic]

NigelS,

If your stock injectors measure 3ohms, then most likely your fuel injection system is of the Peak & Hold variety. A 16ohm injector is most likely an injector for a Saturated type system. Using the incorrect type of injector will most likely damage the ECU's injector drivers. If the unit functions at all.

Good Luck
Bryan Carter

 

[fhperez]

Well i agree it will deffinately destroy your ecu's injector drivers, i have seen this happen before and its not pretty, one thing to do is to put some resistors in parallel to get the ohms down that low but then you would have to play with the amount watts you need..

 

[dgallup]

NO NO NO.

You have what is called a ballasted drive system. The low impedance injector (it is probably more like 2.2 ohms but you need an accurate 4 wire ohm meter to measure small resistances) is in series with the ballast resistor (typically 6 ohms). So the load seen by the injector driver is 8 to 10 ohms. Using a 16 ohm injector without the ballast resistor will draw less current and will NOT damage your ECU. Most likely, your car will also run like crap. You have to match the static flow rate and the dynamic calibration quite closely to make this kind of swap. The static flow rate is straight forward to match but a 16 ohm injector typically has a "dead time" of about 0.9 ms and a saturated injector typically has a dead time of about 0.5 ms. This "dead time" or offset is hard to measure without special flow rigs and almost never published.

So if your ECU sends an idle pulse width of 2.5 ms you will get (2.5-0.5) ms * 230 cc/min = 7.67 mm^3 fuel with the ballasted drive but only (2.5-0.9) * 230 cc/min = 6.13 mm^3 with the 16 ohm injector. Your car will be 20% lean at idle. There are a lot of other factors that will also be off such as the ECU voltage and temperature correction factors. It may "relearn" some of the mapping during closed loop opperation if it has enough "authority" to make such major corrections. However, it will default back to the base programing for open loop opperation (like cold start or wide open throttle) so here your drivability will be terrible or it will stall.

 

[mikikanazawa]

One thing the speed shops in Southern California do, when changing from peak/hold injectors to saturated is simply remove the ballast resistor.

Of course, they're only tuning air/fuel curves to "pretty close" because pretty close is the least expensive way to do it... in the short run anyway.