Would an adjustable fuel pressure rehulator let me tune the A/F a bit closer to optimum while waiting for tuning capability? Any suggestions on how to retro-fit the LS2 with it? I'm at 11.6:1

 

What mods have you done? That A/F is almost a full point fatter than what most of us are seeing in the stock car.

I don't think lowering fuel pressure is the right way to go to fix this. That'll muck up your injector spray patterns. LS2Edit is out, and a number of tuners have it now. So the ECU's fuel maps can be tailored to your car. An alternative would be a piggyback that fools with the MAF voltage to cause the stock ECU to operate in a leaner part of its maps.

 

I think it relies mainly on the O2 sensors during closed loop, also, it will compare that data to the MAF and set a code if they don't match. I don't know why you'd mess with your maps, the risk doesn't outway the benefits....

 

Adjustable FPRs are just another tool in the tuners arsenal. Keep in mind they change the AFR all across the band and if you make too big a drop in FP the fuel injectors don't work correctly (although that takes a pretty big drop).

 

Adujustable FPR do not work on these types of cars. The computer has a set air fuel mixture that it looks for and does what it can to maintain that. When you install a FPR and adjust the fuel pressure it will adjust the mixture for a little while. Through varios sensor readings, the computer creates an L-trim or leaness trim to compensate for the adjusted mixture...seeking that ratio that it was programed for. This includes increasing or decreasing injector pulswidth to compensate for it. It is a completely dynamic system that is always adapting. A similar situation is with massair housings on c-5's. Upon fresh install, the larger housings caused the engine to run leaner, making more power usually netting a few horsepower gain. After driving it for a while, these gains usully dissapeared due to the fact that the computer, for lack of better terms, learned your trick and went back to that AFR that it was programmed for. All this means is that if you want to change your AFR you have to tune these cars.

 

I am familiar with the tuning proceedures and had tuned my C5 for many mods as I got them. In WOT the O2's are not in the system and goes by the fuel pressure as a constant. The PCM does not have a setting for a desired A/F ratio but rather adds and subtracts according to the injector flow rate table from a baseline. If I put smaller injectors in, the O2's would keep the car at 14.7:1 but at WOT the car would run 8% leaner (if I put in 8% smaller injectors.) This is te same as decreasing the injector flow rate by 8% on that table as I did it on LS1 edit for my C5.

If you drop the fuel pressure it will lean out the mixture in WOT.

As long as the LTFT's stay under the +20 range the car will remain at 14.7 in closed loop.

Te beta versions of LS2-edit are incomplete and not available for sale to the individual user. I will have to wait for the official release of the locked version for that method of tuning and I was just looking for a method of adjusting this pig-rich A/F ratio. I doubt there is any stock car out there within a point of 13:1. My C5 was at 11.8 before I touched it.

The MAF tuning tools like the MAFT would allow you to adjust the LTFT's for closed loop and adjust separately for WOT a/f but not customize the curve over rpm and engine load.

My queston wasn't what was optimum...that would be a full dyno tune if there was good software out. Until HP tuners or LS2 edit is finalized I will have to wait. I do mods regularly and it would be inefficient to pay 500 bucks for an incomplete bete-edit tune that I would need to redo for each cam I play with. I was just thinking that if I converted to the 97 adjustable fuel rails I could drop the pressure to lean out the car and check it on my wideband.

 

Correct about the codes. I had a lot of problems when I initially tried to adjust the MAF table for LTFT's and removing the screen. As far as why I would mess with the fuel mapping....11.6:1 isn't good and I can't run this way indefinitely. When you mod your car it changes the fuel curve. The only risk is not tuning.

 

Spin....I dumbed down my answer because I did not know your experience. I thought that you were just a newbie...I apologize. I still believe that the computer will "learn" the regulator as what happened in the 97-98 cars. Having worked for Xtreme Motorsports through college, we dynoed many 97 cars including camaros with the FPR. (Including then worle famous Snowman's Snowmobile) Reguardless of how it happened, they always lost the gains picked up from the FPR after dynoing weeks later. I noticed this exact phenomenon with the larger MAF....Breathless's to be exact. Also I notice the wideband readings returning back to stock (give or take a little) weeks later after both mods. It might not necessarily learn the mixture changes from the o2 because you are correct about them being ignored at WOT. I believe that it is learning and compensating using the trim tables via the knock sensor readings. As you probably know, the computer compensates for knock by both decreasing timing and enrichining fuel.

One more point....and let me know if I'm wrong...it has been MANY yesars... In order to install 97 lines won't you have to install a fuel return? When GM moved the fuel pressure reg to the back of the car, they eliminated the return line....thus the later model cars having only one line passing through the coil covers.

I have been out of the Corvette performance for years! I graduated college three years ago. Even thought I still keep in touch with Nate, I just as soon drive them instead of messing with them.....
Good luck!

 

Surprises me that the FPR turned up no change after the PCMruns a while. I will just have to wait for a valid tuning tool before doing some mods.

 

It is my understanding that with a returnless fuel system that you can not use a fuel pressure regulator.