QUICK QUESTION INJECTORS/GROUND LOOPS

Engine at idle in a car, alternator is not working so the battery voltage is around 12V. We connect an external battery charger to replicate the function of the alternator, and the battery voltage increases to 14V. All other variables about the engine (speed, load, air-fuel ratio) remain the same, but the injector pulse duration reduces. Why? What would happen if it did not reduce and instead stayed the same?

Can someone explain if it is indeed possible for the injector pulse duration to decrease and what would happen if it doesn't. also is there a missing factor on the question for them to conclude that injector pulse reduced.

Here is another question :

What is a ground loop in the context of an EFI system? How would you detect it if you were at the car (eg with a multimeter)? Can you think of a way to detect it by reviewing a log of data from the ECU? Can you think of anything that could be built into the ECU to make the detection easier?

Hey TSIKOY! To be clear, you noted a shorter injector pulse width with the battery charger installed, and a longer pulse width without it?

I can't say I've ever observed that. :blink: Just for giggles, I went and tried it with my own car - the pulse width didn't change with battery voltage. That doesn't mean your observation was wrong, just that I couldn't reproduce it.

I can speculate, though! :lol: For our reference, what's the year/make/model? If this is a PCM controlled alternator, then the pulse width change may be in response to setting a fault code related to the alternator.

Sorry, I'm unfamiliar with the term ground loop. Is this the general idea ?

I think I have figured the injector pulse width issue out, with the battery at 12v the alternator regulator is trying to get the alternator to produce over 13 volts so the rotor coils are full fielded, but probably due to a diode fault or shorted winding all the energy generated in the alternator stator is getting wasted.
With the charger connected the alternator regulator sees a full 14v so shuts down the field coils in the rotor, so and less energy is getting generated and wasted internally and the load on the alternator is near zero. This in turn reduces the engine load and injection durration. I would expect also to see a change in IAC position. MAF airflow or MAP and calculated load,

You can replicate the effect in a car with a working alternator. let the engine warm up and watch what happens to the injector duration and calculated load when you turn all the electrical loads on. On a small car at idle the injector duration can double with all the electrical loads and AC on, you can even see a blip from power steering load if you turn the steering wheel.

Thanks Tyler and Andy for giving time to give answers.

With everything being said, can we see physically that the injector pulse duration reduces. Would a misfire indicate the injector pulse is reducing or we need to hook up a tool to measure it and prove that it was indeed reducing.

With regards with ground loop can you shed some light Andy

TIA
Tsikoy

To look at injector duration requires either a scan tool or an oscilloscope. Misfires really mess up fueling , the injector durration goes up. You can see this on an engine with a badly leaking exhaust valve the fuel consumption goes way up. The reasons are that apart from the remaining cylinders having to work harder the upstream oxygen sensor is fooled by what it detectss as a lean mixture so the fuel trims are ramped up.