I have the basic bolt ons and now a Vortech FPR...just curious what everyone runs at. I think stock is around 50 psi, correct me if I'm wrong.

Thanks in advance.

 

stock is 47-54

 

.....yeah btw, what was that rumor about obd2 trimming fuel press. if you raise it?

True or not?

 

the ecu cannot trim fuel pressure
however it does trim open loop injector pulse based on closed loop operation

 

and it WILL trim based on changes in fuel pressure....that is its primary purpose.

its not a "Rumor" at all....

-dw

 

In stock form with just bolt'ons.. my motor saw little to no gain from fuel pressure changes. If anything, it would make LESS power.

But once I installed the ported head and slightly raised the compression(11:1), the FPR netted almost 5-7whp on the dyno. The motor really liked the extra fuel pressure I gave it(57psi).

Also, on a B20 I just dyno'd this past week, 15 HP and 13-15 TQ was gained by fuel pressure. Yes, it's a big gain.. but I was hella surprised.
It rolled up with 310cc injectors at 45psi... I bumped it to 50psi and the midrange from VTEC on (4800-7000 or so) literally went THROUGH THE ROOF.

That's a perfect example of knowing how important fuel pressure is. All it takes is 3-5psi for a big difference in power output.

Sorry I strayed off topic a bit...

 

I know steve uses obd1 mostly, so maybe that's why?

I'm obd2, so how to combat the ecu compensating? (And please don't say replace ecu...)

 

i cannot base anything on fuel pressure since it cant know fuel pressure.
It bases its "long term fuel trim" on O2 readings during closed loop
and modifies open loop operation accordingly.

 

on me!

 

now are you guys talking with the vaccume line on with 45~50psi or with the line off.??? just a little lost thats all


[Modified by JDM_DOHC_SiR, 8:31 AM 1/11/2002]

 

you always measure pressure with the line off. otherwise the reading doesnt mean
a thing.

 

Thanks

 

true in a very technical sense, the ecu cannot (or does not) measure fuel pressure itself directly. BUT. since the injectors are calibrated to deliver a specific volume of fuel with each pulse for a specific fuel pressure any increase or decrease in pressure will result in a rich or lean condition (in relation to the stock values) which is inturn is read by the o2 sensor and then the injector pulse is "trimmed" accordingly to compensate and return a/f to the stock value. The net result is that the injector delivers the same output volume as it would have under stock conditions...either way. every immediate adjustment by the ecu to the pulse value(short term trim) is saved to memory and an average trim (long term trim) is applied to the base map values so the short term adjustments don't need to be as large, (this is why open loop is adjusted as well). The sytem is in place to compensate for changes or problems in fuel delivery system, like a clogged fuel filter (drop in pressure), which would cause dangerously lean conditions if not compensated for...but it works both ways adjusting for rich conditions too, like a faulty stock fpr or like us cranking up an adjustable one. And this is not unique to obd2, but exists in obd-1 sytems as well.

that is why I say "it will trim based on changes in fuel pressure"....not because it reads fuel pressure, but because it reacts to it.

only way around it is w/ an SFC or custom ecu program...an fpr alone will not do it. Yes you will see dyno plots change when you adjust the pressure on the dyno, but I'd bet if you returned after a day or two of driving, you would see the changes go right back....

-davew

 

davew: you sound like you're very knowledgeable. laymans terms: you know your ****.

always good when H-T gets new recruits that aren't straight outta CSi

 

I understood this is what you meant, i just thought it best to clarify a bit
for others' sake.

 

thanks dad

 

.....ok, then would it be safe to say it's ok to reset the ecu every once in a while to get this long term fuel trim out of the ecu memory?

 

at first i thought this as well, but i ran for quite some time without
resetting the ecu and power output didnt change as much.

 

So is that mean with a FPR alone is not good enough?
How to compensate it with the VAFC?

I am a bit loss here and I will go dyno soon, can someone please explain what I have to do on the dyno with the FPR and VAFC to get the fuel map that I need?

 

increase fuel with the fpr and lean with the vafc

 

Thanks for all the help sgT, hope I will do good when I finally get to tune my car!!

So is there a max amount of % that I can use the VAFC to lean out?
I mean if I rise the pressure to 55psi and then go -5% on the VAFC, should I rise the pressure to 58psi and then go -10% on the VAFC just to run higher fuel pressure?

 

Just to run higher pressure? i dont get it.
you cant equate fuel increase to % of the vafc, because that % number is
a percentage of the map sensor VOLTAGE.

 

Opps, I always think that when you run higher fuel pressure, it mean you are running richer, so I will need to use the VAFC to lean it out!! My bad, just learn something new again today!! Thanks sgT!!

 

when u increase fuel pressure you do run richer.
but the idea is not tojust increase fuel pressure and then go back and lean everywhere
you want to richen with the fpr, then lean out where needed with the afc.

 

OK, so just increase the fuel pressure to a point that I won't need to use the VAFC to add any fuel will be the best?
Sorry for all the stupid questions, I have to admit that I don't know **** about fuel tuning!!