Fuel Pressure Question (42s and no FMU)

[Pull_T]

My fuel pressure is 30 according to the gauge at idle and I see just a hair over 40 when I get to max boost (just about 10psi)

Does this sound correct? I am worried that is too low.

I have a 98 Cobra with an aftercooled S-Trim, 42s and 80mm Lightning MAF being the pertinent mods.

Also, what is a good cause for running inconsistently? Some days it'll run perfect, and others it won;t even want to idle and it'll stall out. I am thinking I need to clean my MAF because a mechanical problem should always be there, so I figure it's electonics of some sort.

[DarkShadowZ06]

sounds like you may need a boostapump or upgrade your fuel pump... I usually get 45 at idle and then it goes up from there.

[txgti]

Todd... I've got my fuel pressure set around 38-41 at idle... depends on temp of engine, and ambient temp. When it spikes it spikes up towards the 85 psi region.

My fuel system....

255 in tank. ATI's version of a t-Rex inline. FMU. 36# injectors. Pro-M Maf. Adjustable FPR.

In your case... with 42s.. you should be fine with no MAF, but in this case... I'd consider upgrading your Fuel Pressure Regulator. SX offers one that is boost sensitive, similar to an FMU, but nowhere near the degree of power rob that FMU's have (from what I hear... I've never actually run one). I would also consider HEAVILY... upgrading to a 255 in tank. The inline pumps (a-la t-Rex, etc) all they;re basically doing is keeling the fuel rails pressurized when you let oiff fo the gas. What's keeping the fuel lines where they need to be... that's teh in-tank.

The other thing to consider at this point, before spending money on a fuel system... is "How far do you intend to take this car"

You'll shell out 5-600 bucks on a new pump, Adjustable FPR, Installation, and a few other assorted things.

If you ever plan on going further... It'd be a good idea to start going all the way and installing a real fuel system with braided lines, AN fittings, New fuel Rails, etc. You're close to achieving the best you can on the stock fuel rails and lines. Those injectors are pretty close to topping out too.

[Pull_T]

I guess my next avenue will be to put an intank on it. All i have right now is the TRex.

$5-600 is no big deal Marc. I;ve already put so much into it, that I need to see it through. I am not going to go above current power levels though, so I don;t want to upgrade rails or anything like that.

[txgti]

I guess my next avenue will be to put an intank on it. All i have right now is the TRex.

$5-600 is no big deal Marc. I;ve already put so much into it, that I need to see it through. I am not going to go above current power levels though, so I don;t want to upgrade rails or anything like that.

The in-tank, Adjustable FPR, and the JMS chip you've got in the works oughtta get you sorted out jsut fine then I would think. ;)

THat's about what my plans consist of... except I've already got the parts you need. I jsut need 42s, a MAF recalibration, and to yank OUT my FMU. ;)

[Redsnk95]

The base fuel pressure is just too low. Your getting the proper raise in the fuel pressure with the 10lbs of boost (being 1:1 with your regulator). Just raise up your base fuel pressure and you should be fine. WIth 42s and 10lbs you need to be around 49-52lbs of fuel pressure (as a good safe starting point).

Troy

[txgti]

The base fuel pressure is just too low. Your getting the proper raise in the fuel pressure with the 10lbs of boost (being 1:1 with your regulator). Just raise up your base fuel pressure and you should be fine. WIth 42s and 10lbs you need to be around 49-52lbs of fuel pressure (as a good safe starting point).

Troy

Troy hath spoken.

[Pull_T]

The base fuel pressure is just too low. Your getting the proper raise in the fuel pressure with the 10lbs of boost (being 1:1 with your regulator). Just raise up your base fuel pressure and you should be fine. WIth 42s and 10lbs you need to be around 49-52lbs of fuel pressure (as a good safe starting point).

Troy

How do I raise my base FP?

[txgti]

How do I raise my base FP?

Strangely enough.. with an Adjustable Fuel Pressure Regulator. ;)

:D

[Pull_T]

Strangely enough.. with an Adjustable Fuel Pressure Regulator. ;)

:D

Well, that I know Marc :p

Is it easy to change (and install) and set?

[txgti]

I had my buddy Phil do mine... From my understanding.. it sits ont he back of one fo the fuel rails... kinda a PITA to get to. You set it by watching the fuel pressure gauge... so if you don't have one of those (which I tihnk I remember you DO have one).

Shouldn't be too tough for you though Todd. I bet you could handle it.

I can probably get you a GOOD discount on SX equipment if that's what you decided to go with... but you might do a little looking. Kirban, Aeromotive, and a few others make Adjustable FPR's too. I'm not too too familiar with the options on the 4.6 DOHC.

:)

[STROKD]

The base fuel pressure is just too low. Your getting the proper raise in the fuel pressure with the 10lbs of boost (being 1:1 with your regulator). Just raise up your base fuel pressure and you should be fine. WIth 42s and 10lbs you need to be around 49-52lbs of fuel pressure (as a good safe starting point).

Troy
I am new here, and don't know any of you guys, but what kind of JANKY ass tuning are you doing on your cars?!!!

49-52 to start? are you tuning a nitrous kit for a 300 shot with 24# injectors or a S/C 42# car?

Pull T, this is from experience, not blowing shit out of my ass to look cool. I have 2 S/C cars, both making WELL over 500 to the tires, TUNED on pump gas, and are driven often. One actually has 42# injectors and NO FMU... FMUs are for lame ass retards with no knowlegde of tuning a computer. What you need to do is set it at about 38-40 psi with the vaccum line off at idle, should be about 30-34 with line on, depending on your vacuum, and do some pulls with it on the dyno. Set the A/F curves in your tables at Wide Open Throttle (WOT) to be in the 11.2-12.0 range. The higher the # the leaner the tune and more power it will make to a point. After that point you are ****ing shit up inside the motor, so the safe spot on the dyno is 11.5-11.8-1 air to fuel ratio, this puts you right around 12-1 on the street, as there is more load on the motor with it moving the entire car, instead of dyno rollers. I hope this gets you in the ball park. 49-52 is just plain retarded. :rolleyes: BOTH of my Stangs sit at 30-31 psi at idle with the vaccum line on, and both hit perfect 11.5-12.0 curves on the dyno.

[Redsnk95]

I am new here, and don't know any of you guys, but what kind of JANKY ass tuning are you doing on your cars?!!!

49-52 to start? are you tuning a nitrous kit for a 300 shot with 24# injectors or a S/C 42# car?

Pull T, this is from experience, not blowing shit out of my ass to look cool. I have 2 S/C cars, both making WELL over 500 to the tires, TUNED on pump gas, and are driven often. One actually has 42# injectors and NO FMU... FMUs are for lame ass retards with no knowlegde of tuning a computer. What you need to do is set it at about 38-40 psi with the vaccum line off at idle, should be about 30-34 with line on, depending on your vacuum, and do some pulls with it on the dyno. Set the A/F curves in your tables at Wide Open Throttle (WOT) to be in the 11.2-12.0 range. The higher the # the leaner the tune and more power it will make to a point. After that point you are ****ing shit up inside the motor, so the safe spot on the dyno is 11.5-11.8-1 air to fuel ratio, this puts you right around 12-1 on the street, as there is more load on the motor with it moving the entire car, instead of dyno rollers. I hope this gets you in the ball park. 49-52 is just plain retarded. :rolleyes: BOTH of my Stangs sit at 30-31 psi at idle with the vaccum line on, and both hit perfect 11.5-12.0 curves on the dyno.

OK slapass, maybe you didn't realize that when I said 49-52lbs of fuel pressure....I am not talking about base fuel pressure. I am referring to fuel pressure at max boost. If you can do the math, that will have the base fuel pressure will need to be set at 38-39lbs...then with 10lbs of boost with the 1:1 regulator that will put him around 50lbs of fuel pressure at max boost. But then again I guess I am blowing hot air here since my car also makes 550rwhp and passes emissions same as your car. I agree with your post and the information for the A/F ratio as that is where I run mine...unless running my A/F ratio at 11.5:1 is "just plain retarded" as you so simply put it.

Troy

[STROKD]

OK slapass, maybe you didn't realize that when I said 49-52lbs of fuel pressure....I am not talking about base fuel pressure. I am referring to fuel pressure at max boost. If you can do the math, that will have the base fuel pressure will need to be set at 38-39lbs...then with 10lbs of boost with the 1:1 regulator that will put him around 50lbs of fuel pressure at max boost. But then again I guess I am blowing hot air here since my car also makes 550rwhp and passes emissions same as your car. I agree with your post and the information for the A/F ratio as that is where I run mine...unless running my A/F ratio at 11.5:1 is "just plain retarded" as you so simply put it.

Troy
I didn't realize, and I do know that it will peak up there with a standard fuel system. I thought you mean set it there at base, and was thinking god damn that is a lot of fuel PSI! :up: :retard:

I have a stage 3 Aero system on my car, and it peaks at like 42-45 or so @ 15 psi... but I set mine at like 35 with the line off, because I have 85# injectors and a F.A.S.T. ;)

The stock set up is at 38 at idle and I don't think it has a 1-1, as it only sees about 40-42 psi @ 11 psi of boost WOT.

[txgti]

So u guys know.. redsnk95 has a board that might be of interest to you guys...

www.stangtuning.com (http://www.stangtuning.com)

There's a lot of info out there that will be extreemly helpful. ESPECIALLY to FAST users. ;)

[VibrantRedGT]

Man that was funny to read.

-Slapass