I'm very aware that this isn't the best tuning device evAr, so no need to remind me haha.

With that out of the way, on to my questions...

I'm looking for tips/advise from people who've tuned using a VAFC (or similar) in conjunction with an adjustable fuel pressure regulator.

I have a VAFC 2, ADJ. FPR, Fuel pressure gauge,and AEM UEGO wideband o2 setup, so I can safely street tune this setup. In the long run, I do want to have it fine tuned on a dyno, however, for the time being I'd like to get it relatively close.

I know that it's best to ADD fuel with the FPR to the point where it's rich and SUBTRACT it with the VAFC to get it where you want it, as this advances ignition timing. My question, is how rich do you want it before you subtract fuel.

As it stands right now, my base ignition timing is set at 17.5* advanced, my fuel pressure at idle WITH vacuum is ~40psi. With no adjustments on the VAFC this equals a low 12:1 afr at 5000 rpm dipping to ~11.8:1 by fuel cutoff. I then used the vafc to MINUS fuel to the point where it is 13:1 AFR from 5000 to fuel cutoff. To get the AFR to 13:1 at fuel cut I had to minus 14%. Is that excessive? Does this sound like I'm on the right track? The car feels great but I know the butt dyno is a terrible way to tell.

So I guess basically, my question is, how rich do I want to make it before I minus fuel? And what kind of numbers to I want to see on the VAFC, like what is considered excessive?

Sorry for the long post, haha I like to be really thorough. If you need any more information to help me out just let me know.

 

first reset your ecu the proper way(pull ecu fuse, leave out a few min, replace, start car and let idle till completley warmed up, drive around normally for a bit, park and let idle, shut off.)

next, change low throttle to 25% and wide throttle to 60%. start the car and adjust idle AFR. Go drive around and watch the wideband while letting the rpms slowly climb @ about 25% throttle, in third gear. this is so you can get the part throttle AFRs sorted. the stock ecu will always hunt for 14.7 in closed loop and go rich at about 4000rpms. make some adjustments if there are any dips or spikes. try to keep the throttle steady.

next you need to adjust the vtec point if you have mods that require you move the crossover. vtec should be seamless not a jolt once it hits. place the vtec crossover 200 rpm before the low cam torque dies off(butt dyno). always do your WOT tuning runs in third gear because every gear will have slightly different AFR, so tuning in third only will get you the closest. only richen the FPReg till you get rid of the highest lean spike in third at WOT. you can manipulate the rpms in the low cam/high cam tables to get more tuneability in problem areas. stock ecu wont see anything past 15% leaned out on the vafc if im not mistaken.

some engines make more power on the lean side and some on the rich side. youll never truly know the torque curve youve created till you dyno tune. 13.1-13.9 is a good area to stay in for WOT without having to worry. you have a wideband at least so youre not completely lost. dont forget to reset the ecu again once youre done making changes. "street tuning" takes tweaking to get right so be careful when doing WOT runs around your town.

 

considering you are are street tuning the VAFC, I would not run any leaner then 13.5 It's safer to be on the richer side then to be too lean; not worth the extra couple horses. As far as your theory to adding more fuel pressure to raise timing; I don't think I've ever herd of that method? If you have the usual bolt-on's I see no use for a FPR.

Good luck and have fun!

 

With all of the bolt ons my car has (Everything that you can possibly do without going inside an engine, including a quality race header not an off the shelf POS, intake mani, TB, 3" exhaust, etc) the car was runing high 13:1 - 14.0:1 AFR at WOT, so more fuel was in order. If you add fuel with a VAFC, due to the way it alters the signals between the sensor and the ecu, not only adds fuel, but simultaneously retards the ignition timing. So, it is more beneficial if you add fuel with an ADJ. FPR, and then minus fuel with the VAFC, as this adds fuel and Advances ignition timing, a win win, to a certain extent of course, and exactly to what this extent is, is what I was inquiring about. Thank you for your response though, and I agree, with your typical run of the mill bolt ons you find on most Preludes, an FPR would probably be overkill.

 

From most of the reading I've done on this, it is recommended that low throttle be set to 90% and high to be at 91%. Most peoples reasoning is that this most closely replicates when the ECU would regularly go from closed to open loop. If you set low to 25% and high to 60%, what would happen from 26% to 59%, would the car just run on the stock map? I'm just curious where you got this setting from.

That's what I figured, I've been doing the pulls in third but it's nice to have that confirmed

I'm thinking I'm gonna wait on this till I get it on the dyno, I feel like my butt isn't accurate enough to out due Honda's factory setting haha, I'm mostly aiming just to get the fuel in a good spot for the time being

I've heard if you go more then 20% you'll throw a CEL, I can't confirm this though, but either way 15-20% area sounds about right.

Thats true, hopefully it wont be long until I have the funds to get it on the dyno, for now I'm shooting for 13.0:1-13.5:1 , I'm sure it'll be better then the 14.0:1 it was running with the stock FPR, safer at the very least.

Haha yea, it was one of the first modifications I did to the car back in 2004 before I did anything serious to it just to keep an eye on things, it's been really handy over the years.

Thanks for the thorough response man, reinforced a lot of what I was doing so at least I know I'm on the right track.

 

The vafc will interpolate the values between 25% and 60%. the low throttle tuning with a vafc is more difficult since the stock ecu will be making is own adjustment while in closed loop. It's possible though. It's sorta fighting with the vafc in closed loop.

 

I get what you're saying, I think the reason we're having some miscommunication is you are mixing up open loop and closed loop, my post may make more sense if you reread it after this;

OPEN LOOP - This is the mode your ECU is in until the coolant temperature and a couple other sensors get to operating values. This is also true when you are at WOT.

CLOSED LOOP - the ecu uses information primarily from the Oxygen Sensor and adjusts fuel delivery and timing to achieve minimum emmisions, better gas mileage and part throttle power.

I'm not even worried about tuning for part throttle at the time being, I'm mainly concerned with OPEN LOOP/WOT tuning. And the whole interpolating thing is interesting, good to know though.

 

yeah you know what i meant......didnt even realize i swapped the two. sorry, fixed my posts. give the vafc manual a read again. it might help some more.