Fuel Pressure question

[TheStock]

After reading the few threads I could find on fuel pressure, I came to the conclusion that with an aftermarket FPR the psi should be at 42.5 or 3 bar and should be adjusted at idle with the vacuum line removed. At idle, with the line connected, the gauge was bouncing around 45 or 47. When I removed the vacuum line the psi jumped to around 55psi. So I adjusted it down to 42.5 and reconnected the vacuum line and now it sits steadily at about 42.
I was wondering if there was any reason why the pressure was set so high and since it was, if there would be any effects? My car has the GURU MAP, 3" exhaust, and running about 16 psi of boost. I took it out afterwards and it seemed to be better, but I could be imagining things.

[nize]

if it's set too high, it will just dump more fuel, and your performance and mpg will go down.

if it's set too low, it will lean out at high rpm's and you'll blow your motor.

[todd951]

The stock fuel pressure should be 2.5 bar. Some aftermarket chips require a 3 bar fpr.

[TheStock]

Originally posted by nize
if it's set too high, it will just dump more fuel, and your performance and mpg will go down.

if it's set too low, it will lean out at high rpm's and you'll blow your motor.

So, in your opinion do you think that the 55psi (or 3.8 bar) with the vacuum line off was too much? Or do some run that high of a pressure?
Also would like to add that if anyone happens to be in the Oregon PCA and is attending the PIR meet on the 12th, I look forward to meeting some of you.

[nize]

55psi at idle is too high. it should be at around 36psi at idle on a stock car.

do you know if you have stock injectors? you should also ask guru racing what the fuel pressure/injector requirements are for the chip you have, i know they have more than one chip.

what other mods does your car have?

[TheStock]

Originally posted by nize
55psi at idle is too high. it should be at around 36psi at idle on a stock car.

do you know if you have stock injectors? you should also ask guru racing what the fuel pressure/injector requirements are for the chip you have, i know they have more than one chip.

what other mods does your car have?

Here's the list the PO had advertised:
Guru Racing Stage I MAP with 18psi chips
Bursch Test Pipe (passed Oregon DEQ vehicle inspection)
Custom 3" exhaust from test pipe back
3 Bar FPR with fuel rail guage
Boost Sciences Accuboost MBC
Nology Hot Wires
Mille Miglia Cup 2 17" wheels
4 new Yokohama AVS ES100 tires at 83K miles
4 wheel alignment by Sunset Porsche
Koni Yellow rear shocks
New drive shafts at 82K (04/05)
Major service by Don Istook in Fort Worth, TX (04/2003) along with new Lindsey Clubgate wastegate, waterpump, and radiator ($2800 total cost)
Shorten shift kit with MOMO carbon fiber and leather knob
Speed 6 Billet Blow Off Valve
Lindsey Racing Vacuum hose kit and Venturi delete kit
New rubber seals on rear hatch and driver's door.
Dan Wray "Lightshark" Full Boat Lighting Kit
Silverstone bulbs in Fog Lamps
VDO boost gauge in dash panel
Carbon fiber dash/door kit
New "Batwing" lower front valance (05/03)
Clarion CD system with Kicker amp, woofers, and door speakers
Sidewinder remote alarm with power door locks

[nize]

also, how do you know what your fuel pressure is?

[TheStock]

Originally posted by nize
also, how do you know what your fuel pressure is?

Well, I pinch one of the lines and time how long it takes return to it's full radius. Then I compute the weight of the fuel versus the diameter and... just kidding.

There's a fuel pressure gauge on the rail. One of the lines of upgrades above mentions a 3 bar FPR with gauge on rail.

[nize]

ah okay i missed it.

it's possible that the p.o. had it tuned for higher boost and more fuel to match the chips. what boost does the gauge show?

maybe it's time to dyno the car and see the actual a/f graph. if you turn this down too much without knowing the a/f, you could do serious damage.

[TheStock]

Originally posted by nize
ah okay i missed it.

it's possible that the p.o. had it tuned for higher boost and more fuel to match the chips. what boost does the gauge show?

maybe it's time to dyno the car and see the actual a/f graph. if you turn this down too much without knowing the a/f, you could do serious damage.

A dyno is an excellent idea, except I've never been to one and have not a clue what all goes into it. There's a TorqueFreaks in Portland that I've been looking at on the net.
The car is running at about 16psi of boost from what I can see out of the corner of my eye while I'm driving, maybe 16.5. The PO had it at 17.5 when we did the exchange, but I decided to turn it down a hair. The FQS switch was set at the 4th position option that gave it a 2 degree ignition retard. But I went in and changed it back to the "0" position which is GURU optimized 91-oct. (R+M/2) pump gas up to 18psi boost with stock injectors. Here's a link to what I'm talking about. FQS Adjust Not that I really know what the difference would be between an advance or retarding the timing, but I'm not doing above 18psi. I wish I knew how to use this GURU system; have tried reading through all the "steps", but still not understanding.

[nize]

how far are you from seattle ? i organize group dyno days at carb.conn in kirkland once or twice a year, if you can wait for the next one in about two months.

[TheStock]

I'm in Vancouver, so anywhere between 2-3 hrs depending on the traffic and what-not. I'll probably take you up on that offer, although I think I might try and get it in to one in the next couple weeks just to make sure I'm not running it dangerously. I'm going to the PIR for the post-parade driver ed on the 12th and wouldn't want to screw anything up if it can be avoided.
Good to know that you're not too far away.

[nize]

i can make it from seattle to vancouver in 1.5hours, so you can too!

[TheStock]

Have an appt. with TorqueFreaks this Sat. (7-29-06) at 10 to do a dyno with air/fuel to see where it's at and maybe some tuning. Will post results as soon as I have them.

[TheStock]

Ok, so I have the results. Doesn't look too horrible from the start, but nothing too great either. The blue is before the adjustments, green afterwards. As you can see, there was a real nasty spike from 3k to 4k RPM which got leveled out. From what the tuner was telling me though, my fuel was maxing out at 5k RPM which seems kind of odd. He says I have the pressure adjusted correctly, but apparently I'm maxing the injectors out already. I don't know, the pump should be good up to 500hp from what I've read. No matter how much he tried to crank up the settings above 5k, nothing would change the line. So I might put a methanol/ water injection system in before I hit the tracks in a couple weeks. From what he was saying, it's in the danger zone above 5k running around 13.2-5 AFR. I wanted one anyway...
I just realized it's too small to see the numbers. Blue run was 234hp and 263tq, green run was 236hp and 275tq.

[nize]

looks good after the tune. do you know if you have stock injectors?

[TheStock]

Originally posted by nize
looks good after the tune. do you know if you have stock injectors?

They are indeed stock injectors, although from what I read I thought the stock fuel system was good up to 275'ish hp.

[TheStock]

Ok, so I have the appt set to get the methanol injection put in and to have it tuned on Friday (Aug 4th). Will post results when I get them.

[nize]

wow that's cool. would you still be interested in a group dyno day?

[TheStock]

Originally posted by nize
wow that's cool. would you still be interested in a group dyno day?

Hell yeah. Just let me know as early as possible so I don't plan something that day.