I have not messed with my tune in some time but somthing has been bugging me since I droped in the 383 over a year ago. I had two reputable tuners work on the tune originaly and had the same problem with both tunes. The first was a mail order tune that I got to fire the new motor with, I provided all specs for the motor including heads, CR, Cam, exhaust, and injector specs. The second tune was on the dyno using the wideband. Well that is the background now here is the problem I find that the injector constant has to be set to a much smaller injector size then what I am running. For instance my 36 FMS injectors are use a 31.5 constant to get my BLM's in the 128 range, and a set of 42's I installed had to be set to 38 to get the BLMs to 128 across the tune. I have 13#s of vacuum and the BLMs are consitant across the board. I do not have an exhaust leak and the car runs great (27 MPG Hwy, 400+RWHP@ 13:1 A/F WOT). Is this compleatly normal or is somthing off? The reason I ask is I just don't see how w/o changing the MAF tables you can add fuel w/o changing the injector constant for part throttle tuning. I have ran V/E master a time or two with no real big changes. I am currently running a tune I put togeather for part throttle and had the WOT tuning done on the dyno on top of my tune. The MAF sensor is stock so I can't se why I would want to touch the MAF tables and the VE tables don't seem to do a whole lot withe the MAF in line. To do the VE tables I disconnected the MAF sensor and trouble code then ran it is speed density mode then once I had the part throttle BLMs close I hooked the MAF sensor back up and set the codes back to normal. TJ, Alvin any thoughts here?

Thanks Paul

 

To add or subtract fuel you need to either play with the injector constant or MAF tables (not to include PE fuel adders). Even if you are running the stock MAF you may still need to adjust the MAF tables. It isn't about the MAF, it is about air flow through the engine, you need to set the MAF tables to get it where it needs to be.
You use the injector constant to try to fix a universally rich or lean condition (rich or lean in all cells), then tweak the MAF tables to get each one in line that the injector constant didn't fix.
As far as your injector constant not matching your supposed injector flow rates..that happens. To see if it is hurting you, you need to look at your injector duty cycles, if you are at part throttle and over 85%, you need bigger injectors, if you are at WOT and are over 95%, you need bigger injectors (I like the 5% or more safety margin on DC).

 

Morley,
Thanks for the responce. I was using the injector constant to add fuel across the board as you said. Once I did that, the rest of the tune was prety darn close. My DC never gets over 78% so I am good to go there. I kind of knew the answer this question but just wanted some feedback to make sure it was not somthing uncommon. My tune looks good and I have 128-132 for most cells and think it will stay as is till I get the Nitrous installed this summer. Again thanks for the help