Well, I'm glad you got it to work.
But it still makes absolutely no sense to me.
Why in the hell would a 57lb injector need you to use a 45lb injector constant in the pcm?
I'm going to have to do a little digging on this one...

 

Trust me, i'm as puzzled as you. I was really freaking out when it wasn't idling on it's own and running as lean as it was.

The PCM seems to be happy now. I even threw a wideband on it and verified that it's close enough for government work (like i said, i just wanted it in the neighborhood for after the engine swap).

 

Does anyone know what it matters at what duty cycle the injector flow rating is reported?
For argument's sake, let's say that the injectors were flowed at 43psi and 100% dc, wouldn't the injector flow rating then be higher than if they were rated at 80% dc?

 

There we go,

Simply different injectors act differently and fire differently. I wish it was just as easy as pluging in a constant and letting it go but its not. (It woudl get rid of a ton of base files for me).

One thing thats always struck me as odd is that the mustang boys just change MAF sample tubes... So when your doing a car with 55lbs injectors it will have a calibrated (crappy might I add) MAF. If you look in the computer it still thinks its got 24's but it all works out OK because the MAF signal has been cut significantly. I do a few mustangs here and there and you want to talk about nightmare.. jeez.. trying tuning a idle where the MAF voltage seems like its barely showing up.

IN the end, we must realize the computer is stuiped. It just does math and thats it. So even if injector constants or MAF tables or VE tables or whatever doesn't add up correctly as long as the car preforms then well mission accomplished. Some where things are gonig to have to be tweeked.. And if all that you changed was the injectors.. than it only makes since to only play with those values.

We are all guilty of this because if you look in your PE tables alone I guarentee you have fubared desired AFR's. Do it right quick... 14.7/(1+ %Change in cool + % change in rpm)= called for AFR.

 

Theoretically, yes. The flow rating would be higher. How are the stock injectors rated? Also, maybe we should ask Racetronix how they flow their injectors...

As another data point, the INJ DC (calc) was at 132-134 at 5700 rpm and WOT with the stock injectors. It's reading 60-61 now.

 

I guess my corrupt little engineering mentality is causing me to be a little confused at this point. He paid $29 each for new injectors, rated at 32#/HR, and with a quoted constant of 31.6#/HR. They are only flowing 25.3#/HR, and by your logic, that's perfectly OK? He should just reset the injector constant back to stock where it was, run injectors that are no larger than the stockers, and be happy with the results, because he was able to correct the problem simply by changing the constant.

What's wrong with this picture?

(I'm about to resort to the "rolleyes", because this is incomprehensible )

 

I'd imagine that offsets have to do a lot with it... Just look at how different the offsets are between SVO and GM:

http://www.carprogrammer.com/Z28/PCM.../injectors.htm

(Who knows if these are right... I try to verify most things I find on the web with other sources, but can't find much out there on injector offsets.)

I thought about cranking up the offset to get to the same point with the correct constant. It just seemed like it would take a lot more guess work without being able to accurately tweak the offset at all voltages. I couldn't find offset data for the Siemens injectors anywhere.

 

Actually he bought 57lbs injectors.. and found 45 to be the constant

BTW. Changing the offsets are also changing the flow rating in the computer. Its just doing it per battery voltage. You got to ask yourself if thats truely nessisary... to tune in 9v 10v etc or globallly change it with the injector constant. You just need to make a decision on which is easier in tuning the car.. both are fudging the results.

Also on the offset method. You got to realize that there are PCM's without those tables.. Just about everything speeddensisty doesn't have them while it seems just about all the MAF stuff does. ex 86-89 has it but 90-93 doesn't.

 

I think Injuneer was referring to the guy who originally started this thread -- Demus.

 

Exactly!

Demus originated the thread.... he switched from stock 24's to Lucas/Delphi 32's and used a 31.6 constant (he has another thread on another board tiwh the details.) My references were to the original post.

Roadie seems to have hijacked the thread, which is unfortunate. But I think I'd ask the same question about his setup.

 

only one way to know what the offset needs to be, just ask yourself this.
Is my injector on for 1.4 milisecond or 1.0 when comanded for 1.4MS
This is where IOV comes in. Most larger injectors need that little extra dwell [injector offset voltage] bumped into them.
use the offset voltage over false info in base tables.
The main function of "IOV" is due to the charging systems effect on injectors dwell timing and we need a way to maintain the stabilty in "constant time".
You start drawing more on the electrical system and the effect that has is it tells the charging system to crank some more voltage into the system. This causes a richer condition due to the incress in voltage on the injectors.
So the charging sytems "load" would cause huge swings in the injector constant dwell time without this function table.
You may not have access to IOV but its built into all operating systems.

I'm sure steve quinn could shead some light on this as he works at Kinsler

 

Right you are. This is the real.

Offset tables... The crystal ball which holds the key to all injector tuning problems NOT!

Tune for proper A/F, timing, A/E fueling and leave the offset tables alone.

On the Siemens 3172's. We have placed them side by side with 3102's in our flow bench and adjusted the injector supply voltage while running dynamic tests. The fuel delivery stayed within 1% over the entire voltage range we applied to the injectors. The 3172 is a reasonably fast injector for its calibration.

Injuneer is right "He should just reset the injector constant back to stock where it was, run injectors that are no larger than the stockers, and be happy with the results, because he was able to correct the problem simply by changing the constant."

Injuneer I will save you the trouble

 

Thank you.

I guess I really ain't crazy.

 

You forgot to take the square root of the pressure ratio when recalculating the flow constant.... its:

43/40 = 1.075
1.075^0.5 = 1.037



can someone tell me why you would need to square root this number, ive never done that. im just courious why, why not use the 1.075 thats the accuall percent change.

 

The injector is an "orifice", so you use the "orifice equation" to solve for flow vs. pressure. Double the pressure, and you increase flow by 41.4% (square root of 2 = 1.414 )

F2 = F1 x (P2/P1)^0.5

Here's a good reference on injector tech..... scroll down to the middle of the page and read the section on "PRESSURE AND FLOW CHANGES":

http://www.supras.com/~riemer/sonict...rs/RCtech.html