Ronny

iTrader: (1)

Quote: you could try increasing the Injector Bias. That will richen up the mixture by allowing a greater amount of the PW to actually be used and not just open the injector.

that was recommended by one of our members.

could this be explained? how can injector bias affect the A/F in PE?. i upped FP from 17.5 to 20.5 and PE went ONLY from 13.3/1 to 13.0/1. now i need to swap in a diff spring to get 20.5 FP and up. i searched injector bias and cound not find an explanation.

also could anyone define "injector bias" please ?

Dominic Sorresso

Ron,

Think of Injector Bias as Spark Advance. The PW calculated includes the amount of time it takes to open the injector. The Injector Bias is used to begin the injector opening sooner. Basically, its the advance for the injector opening. Increasing injector bias will give you a "truer" effective injector PW particularly in the upper rpm range. With a more accurate representation of the PW, you'll find your commanded AFR will more closely approximate your actual. And basically, I tune WOT first, then the rest of the VE table. First of all I am interested in making certain I have enough head room on the injector PW/DC%. I'll adjust IB and Fuel Pressure to get to an adequate Duty Cycle at WOT-PE, then tune part throttle. For example, my IB is currently set at 701.96mv. That's about double of stock.
Try it. You'll like it.

vernw

iTrader: (2)

So, how do you go about determining the right IB? Not too sure I followed all that.... (or does it matter if I'm using $8D?)

RBob

iTrader: (1)

Injector bias is important. It helps to linearize the injector, and make up for the time to open. Different masks handle this in different ways. For all injectors there is an opening time. This is also affected by the system voltage.

Some masks also have a short PW adjustment.

My bet is the GM gets these values from the injector manufacturer. Same as they do for spark latency times.

With the TBI injectors I have changed the fuel pressure and the BatVoltage to come up with some times of my own. This being measured by physical presence of fuel and current traces.

RBob.

69 Ghost

iTrader: (1)

I have a problem where my PW is just not enough based on what I have. I have been trying to get my AFR's to follow my commanded AFR's and actually posted a thread on the subject. I am running 24lb injectors on a 327 with AFR heads. Interesting enough not one person suggested changing the injector bias. I ended up lowering my injector size to 22lb injectors to try to get the PW's to be large enough in the upper RPM's under PE. I have stopped trying to adjust anything other than my VE tables and timing in OL. It would seem that this would be a good thread to post more information on how to tune the injector bias and what it's limitations are.

RBob

iTrader: (1)

For upper RPM PW I've gone as far as setting the injector flow to 18 #/hr. This was on a 302 with 26 #/hr injectors.

The injector bias won't help much for the larger PW's. It will make a large difference when the PW's are small.

BobR.

Dominic Sorresso

RBob,

Would you agree that IB helps in fine tuning WOT AFR? As I recall, one thing you said was that IB helped in making sense of some of those "hinky" areas in the VE table.

RBob

iTrader: (1)

The injector bias (IB) during WOT is a smaller portion of the PW. If the IB is 700us (0.7 ms) and the PW is 6.5 ms, the IB is about 11% of the PW.

When at low load and a small PW the IB can be a substantial portion of the PW. Take idle with a PW of 1 ms and the same IB of 0.7 ms. Here the IB is 70% of the PW.

I don't adjust the IB for other then low PW situations. If the VE tables start looking bath tub shaped as the low MAP areas increase. Most likely the injector bias is too low. The VE table is being used to make up for it.

RBob.

69 Ghost

iTrader: (1)

Do you have a VE table that shows this? At WOT my PW was maxed out around 8.6ms and I needed probably about .7ms added to that based on other runs where I had up to 30% added to the PE AFRvsRPM in the upper areas when my heads came on. I already had my VE tables at 100%. My goal was to have my actual AFR follow my commanded closely. I have also been having some idle problems. I just recently reduced the injector size to get more PW but also started tuning with the bin in OL. When I get my AFR's following my commanded AFR's I will then go CL and try to fix what is off such as R/L constants, etc to get my VE tables running 128 or so. I went the other way and have had nothing but headaches at idle and WOT.

Dominic Sorresso

This is what I remember you explaining.

RBob

iTrader: (1)

Here is a graph of the bathtub. The area in the blue box is where the issue is. As the MAP drops to 25-30 KPa the VE values start to increase. This is to make up for lack of injector bias.

RBob.

Grumpy

ECM Test Bench, Piezio Electirc transducer (knock sensor), and a dual trace scope supposedly is all you need to check the opening delay/ offset. Then with an adjustable voltage supply you can even do the battery v compensation.

RednGold86Z

iTrader: (1)

I prefer an injector flowbench with a ECM test bench (to generate injector pulses) with a scope to see the actual pulsewidth. Make a curve of flow vs actual pw, and extrapolate to where it crosses zero (i.e. constant frequency; flow (in x amount of time) at 1.5 ms, flow at 2 ms, 2.5 ms, 3, 3.5..... to static. Plot it, fit a line, look for where it crosses zero on the PW axis.) Gives a good characteristic of the actual offset required in application (and can see what really happens at high DC as well).

Do this at different system voltages for the VBatt effects. Takes a few hours, but it's simple and effective.

69 Ghost

iTrader: (1)

OK guys you are over my head! I would love to have a test bench but I don't. I am stuck in the real world testing on my car. Worse yet I only get a run in about once every two weeks if I am lucky. In the past my car was a mildly modified TPI intake and I had no problems like today. When I went to big heads, 1.6RR's, and the LT1 intake that is when things changed dramatically. The eye opener was during a dynorun day when my car went way lean even though my commanded AFR's were rich which only told me how far off my tune really was. WBO2 came onboard shortly there after. I am starting to realize that the CL tuning to get the BLM's in line is a bit of a waste until the you can get the tune to behave like you want it to and the only way is using a WBO2. At that point in time I will switch back to CL and then work on the parameters to get my BLM's to match my VE tables if I decide to ever go back to try to run CL only when I am in a steady state -cruise condition.

Dominic Sorresso

I think you'll find several of us who have advocated the same process. Make sure WOT is getting enough fuel with headroom on DC%, then tune part throttle.