Fuel Injection

Here is a voltage capture of an injector from a 93 Cavalier, oddly enough. You are absolutely correct as far as induced voltage. I can't actually answer the question you ask. One thing about induced voltage in and injector circuit though. There really is no amperage flowing at that time. And, the innards of the PCM are built to withstand it. Injector drivers are known to go, but no more often than other parts of the ECM.



Here is current on the same type of injector. If you look about 3/4 of the way up the pattern, you can see a little dip. That is the actuall pintle opening on the injector. Depending on the injector, you will see the "pintle hump" anywhere from 60 to 80% up the rise of the pattern. I find amperage much easier to use to diagnose these things.

 

I must chime in here!

Upon the release of current to said injector, or coil if you will....the induced voltage, or magnetic induction from the collapse of the feild should not be introduced into the computer being how it is a signal that is SENT to the injector, ....not a signal that is 2-way....or fed back into the compouter....


I may be wrong, and PLEASE correct me if I am wrong!!!!


THis is a new feild for me, and i WANT to be educated in it!!!

 

In a sense, you are right, Viking.

Basically, there is voltage through the coil of the injector, but there is no amperage, or current flow until the PCM/ECM grounds the circuit. There is constant system voltage, and on 99.9% of all cars out there, the computer is what completes the circuit. Nissan is the only one in a very select few years I can think of the the computer sends voltage to activate the injector.

So, for me to be able to get the top pattern, which is voltage, I had to tap into the control, or ground wire going to the computer. So, the induced voltage actually does go down the line to the computer. But, once ground is released by the computer, it is open circuit to the PCM. Not saying it can't jump a gap, but as it is a transistor controlling it, I find that not as apt to happen.

 

Good luck on the finals, Ranger. This will always be here for discussion.

 

Hi there. Installing a capacitor could possibly cause problems. The capacitor would be a load on the pulse from the PCM while it charges, which could temporarily reduce the power available for the injector (since they pulse so fast, this would be an issue). It could open too slowly or not completey and run the engine lean for that cycle. Once the PCM pulse stops, the energy "stolen" from the injector by the capacitor may then discharge back to the injector, holding it open a little longer. This would allow fuel to leak into the cylinder out of time. Most likely it would very slightly delay the opening and closing of the injectors. Who knows, the problem might cancel itself out since the extra fuel drip from the slow closing of the injector might make up for the lack of fuel from the slow opening! If anything that would cause the fuel to drip instead of spray which would reduce efficiency of the engine.

All in all, I'd avoid messing with it since the injectors, PCM and harness are all expensive to replace if something goes wrong (IE: once you cut into the harness it will allow moisture into the wires). Manufacturers spend lots of time and money looking for ways to make cars reliable and fuel efficient so if this would help they probably would have tried it! Anyway, you had a good thought process and your theory is as good as mine since we haven't tested either! If you do try it, let us know if it makes a difference... Take care, Mike

 

Mlelsafe brings up some good points. As far as the engineering of the system. I have to think about what he said though as far as a cap stealing energy. Possible? Still need to ponder that.

Ranger, the site you linked is for a peak and hold injector, which were used on early to late 80's vehicles, and even later in some imports, I believe. Basically, they are a lower resistance injector that the current is limited on once it reaches a certain level. One the pintle is open, it uses a smaller amount of current to keep it open. So during the on, or hold portion GM especially had a problem with what was called ringing. What was going on was fluctuations going back to the PCM. Now, was it actually going back to the pcm, or was it the pcm causing it is the question. I have seen that phenomenom, and it never seemed to cause a drivability issue. Others swore it would. Hard call. But what folks would do is "cap" the injector and it would stop the fluctuations. Some said it needed an ecm, some said cap it, and some said leave it alone.

In your Ranger, you have just a plain old saturated injector. And, I don't think a cap would do much, if anything, in all honesty. But, sliding a cap in the top of the connector wouldn't be tough, and may be worth experimenting with.

 

Here is a peak and hold injector current waveform. I don't have a voltage one as I rarely use it. But, when one comes in, I will be sure and snag it. Each "dot" is one amp, so as you can see, it takes nearly 3 amps to open it, then it keeps the pintle opened with a half an amp of current. Basically, that just means it is harder to move the pintle than it is to keep it open once moved.

Example: When pushing a car, it is most times harder to get it moving than it is to keep it moving.

Hope this helped.

 

Can't beat those Rangers. Mine's a 98, and the wife has a 99. We got her one because the Motego was just to hard to drive when the snow hit.

I have been messing with WinSD and am sort of getting the hang of it. Building a sub box is my next project, I think. Plus, I think I want to make the amp on the back panel look a little cleaner. I liked the wires all exposed and routed with chrome plug wire looms screwed to the backboard, but I think I'm over that. I put the sub amp in the seat cubby, and took off the back of the jump seat so it will fold up. In the winter, cooling isn't an issue, I don't think. Summer time, I fold the seat down though.

As far as keeping the shop clean, I think it's a pride deal. We scrub er down every Friday afternoon, and each tech is in charge of his area as far as keeping it straight. Some keep it straighter than others, which I'm sure you understand.