I recently uploaded another new program, this time I swapped the stock fuel injector offset table with one for svo 42's. I also leaned the injector flow rate table in anticipation of not needing to be as rich to make up for the incorrect offset. It all worked fine, except now at idle it seems like it's staying in open loop. Autotap says it's in closed loop, but the o2's are staying at mid .900's on b1 and b2 usually starts at about .800 and works it's way up to pretty much where b1 is. The ltrims at idle are reading -14, and go to ~ -2 with just the slightest throttle. Got me baffled.

 

You can only go so high with the injector flow rate tables before the PCM begins to flounder in closed loop. This limit is slightly north of 50# injector settings.

If your injector offset table is causing you to run super rich, then you are going to have to shift the offset table to accomodate for rich running condition and try to reduce your injector flow rate table.

Good Luck,
Kevin

 

Ok, I'll play with that some. How does the voltage in the offset table relate to operating conditions? I assume that the higher voltages are higher load conditions. A stronger voltage to open the injector faster?

 

Injector offset is tough to explain without some pictures, but I'll give it a whirl.

The PCM sends out a voltage signal to open the injector. Because of properties of inductance associate with the electrical coils in the injector, the circuit voltage does not immediately go to the immediate desired voltage that the PCM sent out. Instead, voltage has to "build" in the coil first. Once the voltage builds to a certain voltage, the opening voltage, there is enough power in the injector coil to open the coil. Once this 'opening voltage' is reached the injector opens. Mind you this only takes milli-seconds.
The same thing happens when the PCM closes the injector. The PCM takes away the voltage signal holding the injector open. Instead of the voltage in the circuit immediately going to zero the coil slowly 'discharges' the voltage. This means that for some set time after the PCM has removed power from the injector circuit, there is still going to be residual voltage in the injector circuit because the injector coil is still 'discharging' voltage.

This may not seem like a big deal, but it plays a significant factor when you realize that the PCM fires the injectors repeatedly. Meaning just as the PCM made the decision to close the injector, a few mili-seconds later it decides to open the injector again. If the injector coil is still discharging voltage while the PCM decides to open it again, then it will take less time for the PCM to 'build' back up to the 'opening voltage' again because there is already residual voltage in the circuit. Because of this, an injector still discharging voltage will open sooner than an injector that is not discharging voltage. The sooner the injector opens, the longer it stays open. The longer the injector stays open, the more fuel that is added.

The injector offset curve is the PCM's compensation for this delayed voltage discharge of the injector. How much voltage that remains in the injector circuit, and how long it takes to discharge after the PCM has shut off its power to the injector is dependant on how much voltage the circuit uses, the size of the injector coil, and the impedence of the injector coil.

So, to make a long post longer, the injector offset curve can *slightly* alter the pulsewidth of the injector, by skewing how the PCM corrects for the injector.

Good Luck,
Kevin