b16ahybrid

Does anybody know of any articles or posts that explain how the fmu works.Or if anybody could just post here how they think it works.mainly what your fuel pressure would be at with this given scenareo
6:1 fmu, 38psi t idle,7psi of boost....explain how it gets to the final fuel pressure and why...thanks.....I'm trying to explain this to someone and they are having a hard time following,thanks for any help......

Kevin

Basically....It slows the fuel from running back through the return line and into the tank allowing pressure to build up in the rail.

racerxadam

the ratio gives the added fuel pressure per pound of boost like this

38 psi base pressure
6:1 fmu disk
7 psi boost

38+(6*7)=80

80 psi fuel pressure at the rail

so you multiply the ratio by the amount of boost being run and then add that to the base fuel pressure.

b16ahybrid

Thats what i'm looking for,The guy that i'm trying to explain this to doesn't think that the static fuel pressure as anything to do with it.So in his theory under full boost there would only be 42psi of fuel pressure (7psi x 6).which would only be 4psi above static fuel pressure.thanks

Anybody else want to confirm this.........

TurboedGSR

so i guess a 12:1 at 7psi is really dangerous isnt it?
around 124psi at full boost

Overblown-Teg

Turboedgsr look at my post on his other thread.. tooo much pressure. He is wrong. the fmu starts at 0 for every pound of boost it adds it rated psi. if you base pressure is 40 you will not notice the fmu until the ratio exceeds 40. This is on a properly functioning system. there is every chance that the return line is too small for the pump you guys are running and the lines them selves are increasing the fuel pressure.

TurboedGSR

thank you, this is what i've always tought and it has been confirmed in another thread about a month ago but i cant find it, let me try again

b16ahybrid

are you runing a fmu? do you have a fuel presure gauge?
Your theory tells me that at full boost i only have 42psi of fuel pressure. (6x7 psi) what good is a fmu then?So your saying that i could go remove my fmu and sell it because i can just raise my fuel pressure to 45psi at idle and have more then enough fuel for 7psi of boost..oh wait i would have to much fuel pressure because the aem fpr i have adds 1psi of fuel pressure for every psi of boost so i would have 52psi under full boost.Or does the aem fpr work the same way?Because in reality it's the same exact thing as a fmu but it controls the static fuel pressure in vacuume and adds 1psi additional fuel pressure for every psi of boost it sees.So i would need to run 38psi of boost before it would actually add that one psi.Hmm i guess i better call AEM and get my money back because they are misrepresenting there product.....Tell me this.....why would AEM market there adjustable fuel pressure regulator as a 1:1 ratio if it would never ever see enough boost to make use of that function?
Here's another mysterious question what good would a 4:1 fmu diaphram be? it would take 10psi to even equal the static fuel pressure.So i could run 10psi of boost with NO form of additional fuel delivery, **** i think that i will go turn up my boost sell my fuel pump, and fmu so i can but that bigger t3t4 that i want, i was under the impression that the stock honda fuel delivery system was not sufficient for boosted applications..........So why does vortec even make this product, because according to your theory all i need is 4psi of additional fuel pressure for 7psi of boost...i can get that by turning up my idle fuel pressure, and save myself $350............PLEASE find that post that proves me wrong so i can be proven wrong....if i happen to be wrong i will admit it and shut up!
untl then anybody else have any input...................?

b16ahybrid

TECH TALK

FUEL MANAGEMENT UNIT (FMU)

What is an FMU?
The letters FMU stand for "Fuel Management Unit". Basically, an FMU is a fuel pressure regulator. The FMU is used on fuel injected, supercharged engines using the factory electronic engine management system.

When an engine is supercharged the air delivered to it is greatly increased. For the engine to run properly and make max power a 11.5:1 air/fuel ratio must be maintained. Since the factory electronic controller can compensate for this increased air flow (it was not designed for supercharger use) another way has to be found to supply the necessary additional fuel. The FMU is the device that does this.

The FMU is installed just down stream of the stock fuel pressure regulator. It does not control fuel pressure until the engine manifold pressure comes under boost from the supercharger. As the manifold pressure increases, a pressure line from the manifold to the FMU causes the FMU to increase the fuel injector rail pressure. The increased fuel pressure causes the injectors to deliver more fuel to the engine. With this system the stock factory electronic controller can be used without modification on a supercharged engine with good results. The reason the Vortech supercharging systems are smog legal is because the stock controller is retained unmodified and at part throttle the engine's performance and emissions are not effected

It doesnt tell you to much except that it states That it increases the fuel pressure as manifold pressure increases.So in your scenereo it would not be increasing fuel pressure as manifold pressure increases, only once it reaches static fuel pressure,therefor not maintaining an ideal air fuel ratio.There will be more to come.

Zenki James

One thing to add with these FMU talks you can not use a formula to figure otu what your fuel pressure.
On the Dyno you'll see certain pressures once you get over like 4-5psi. On the dyno a 12:1 never got over 110psi at 12 psi and 310cc/min injectors.
4:1 never got over 65psi at 12psi and 440cc/min injectors and these never really changed if I was at 8psi or 12psi.
At one point like the 12:1 your fuel pump will just max out and not push any more psi. This is something to considering when choosing FMU ratio

NuSiEr

The FMU's that i've encountered has adjustable static pressure. Meaning, you can adjust for what the pressure will be when you reach '0' Vacuum. From there, that's where the rise-rate come into effect.

racerxadam is correct about the formula

Like you both said. "There is no way the FMU know's where your initial pressure is set at." What you need to do is disconnect the FMU's Vac. line and adjust your static pressure. When you put the Vac. line back on, it will return to your idle pressure which is controlled by your FPR.



[Modified by NuSiEr, 8:23 PM 11/18/2002]

b16ahybrid

That must be the super fmu
which colaborates with what i've been saying the whole time

NuSiEr

Well. You are slightly wrong too. Your calculations included idle fuel pressure. Idle fuel pressure and FMU static pressure is not the same thing. I think that is where most are confused.

superduperman

with all this FMU talk, what does the inline pump and intank pump have to do with anything?

b16ahybrid

Only the super fmu can control static fuel pressure.the regular fmu (which most have) rely's on the stock fpr to provide the static fuel pressure.The fmu does nothing to the static fuel pressure under vacuume, it is a passive device until boost is generated then it becomes an active device.
If i adjust my static fuel pressure it translates to the final fuel pressure.Meaning if i raise my static fuel pressure 10psi my final fuel pressure under boost will be 10psi higher, i've done it several times so i know it works, i do it at the track when it's warm to provide that extra margine, i would rather run a tad to rich then to lean.plus my combustion is hotter due to the high octane fuel.

TurboedGSR

then you must have the SFMU and have it adjusted to 40psi static then. this is straight from http://www.capa.com.au/vortech_fuel.htm

FMU Operating Description

In Summary, the FMU backs up line pressure at the given rate for this example 10:1, therefore if the original regulator still in place holds a rail pressure of 40psi, it will take 4psi of boost for the FMU to raise pressure to 40psi. At this point there still will be no effect at the rail pressure simply because most factory regulators also raise fuel pressure at 1lbs of fuel pressure per 1lbs of boost. So you would have 44 lbs in the fuel rail and 40 psi between the FMU and the original Reg. But at 5lbs of boost you would then have 50psi held by the FMU thus raising the rail pressure by 5psi. Then at 6lbs of boost you would have 60lbs at the FMU and 46lbs held by the original reg, thus raising the fuel pressure by 14psi. This proccess will increase as boost increases. CAPA does not reccomend running fuel pressure any higher than 90psi. Precautions must be taken to ensure that all fuel system components are capable of operating at these high pressures.

and about the 4:1 FMU, who would use a 4:1 for 10psi? if a 12:1 works for 240cc injectors, the conversion would be 8:1 for 480's and 4:1 for 720's (i know that is not totally accurate) Now how many people do you know that run 720cc/70lb injectors at 10psi?

TurboedGSR

you dont have a stock "honda fuel delivery system" dumbshit, you dont have stock injectors, and stock fpr would not let you adjust for even 4 additional psi

NuSiEr

Ever heard of Cartech?? They have adjustments. Even the Crappy JR FMU has an adjustment.. So no... the super FMU is NOT the only one with static fuel pressure adjustments.

Can you give me your definition of "static fuel pressure" and what are your steps to adjust it?? Just curious..

b16ahybrid

Lets keep the maturity level up at least close to adults.That comment that i made was sarcastic if you couldn't tell.What i'm saying is according to your theory i could go but a $35 b&m fpr and raise my idle fule pressure from 40psi to 44psi and have more then enough fuel for 7psi of boost.Not true.
Exlplain this to me. Why is it that when i changed my fmu disk from a 6:1 to an 8:1 my fuel pressure went up even more at 7psi? shouldn't i have only have 56psi of fuel pressure (at least according to your theory) and not 100+psi of fuel pressure.Even when i had the 6:1 it was still higher then 42psi that according to your theory it should be.I had 90psi 58psi more then your theory.EVERY SINGLE FMU SET-UP THAT I HAVE SEEN HAS WORKED EXACTLY THE SAME AS MINE.
since your theory says that i can run 5psi of boost (being that the fmu doesn't provide more fuel for the first 5psi) since idle pressure is at 40. I should be fine runing a stock honda fuel system (yes stock injectors,fuel pump,and fpr) and still be runing fine..........sorry i'm not that stuipid to think that a stock honda fuel system will provide enough fuel for 5psi of boost.THINK ABOUT IT FOR ONE SECOND.When you add more air you need to add more fuel at the same time.....My engine is not going to burn the extra air that is forced into the engine if there is no additional fuel to ignite it....
Lets test your theory....go unhook your fuel set-up put it back to stock and run 5psi of boost, then we will see how long your engine will last...

_Endless_

since we are talking about FMUs here, i was wondering if there's way to know if your FMU is working fine, like, not giving rich mixture during idle and etc.? is there a way to test it?

b16ahybrid

Get a fuel pressure gauge.

turbosol

I totally support b16ahybrid on this, I tapped my stock fuel rail and installed a pressure gauge, next i got a small hand pump and teed it into my fmu vac hose along with a spare boost gauge that i had and watched the fuel pressure rise as the boost rose. Fuel pressure started rising with the 1st psi of input. Who ever stated that a 4:1 disk would be used with 720cc injectors, I'm sorry but you are way off. 240cc=12:1; 310cc=8:1; 370cc=6:1; 440cc=4:1 keep in mind that this is for turbos. JR kits come with a 5:1 fmu with stock injectors but thier fmu has a preload of 50 psi so that when the manifold reaches 0 vac the fuel pressure jumps to 50 psi. Anyway I hope this helps, I don't mean to hurt anyones feelings but this IS HOW IT WORKS.

b16ahybrid

Hey thanks for backing me up.I watch the fuel pressure rise as boost rises (starting with 1psi) all the time being that i have a boost gauge and fuel pressure gauge mounted in my car.

TurboedGSR

i apologize, it was early and i needed my daily caffeine, again sorry.

maybe you have a sfmu or a cartech's adjustable one, i dont know. I got the info. from the website so either you dont have the same fmu (basic voterch fmu) i'm talking about or the information on their website is false, I have reason to belive what i am saying. I do have a fmu myself but no gauge, maybe i should get one but i doubt fuel press. would be 100psi at 5lb of boost.
and no, my theory does not say you can run 5psi on the stock fuel system because for stock injectors you should use a 12:1 fmu. That means on a completely stock/factory fuel system you could only run 3psi, that seems more reasonable doesnt it.
In a earlier post you mentioned you had 310cc injectors, that is why i said you are not running a "stock" fuel system, now you are saying you have stock injectors with a 6:1 disk, i am confused.

turbosol,
i was trying to prove a point that a 4:1 fmu would not be needed for only 10psi.

b16ahybrid

No your correct my fuel system is not stock, i do have 310cc injectors.The point i was making reguarding runing 5psi on a stock system took the 310cc injectors in to account (so yeah it wouldn't be stock) either way with the 310's 5psi (8:1 fmu) is not possible with only 40psi of fuel pressure.I just worded it poorly.The fmu i have is just the basic one i ordered it directly from vortec about 2 years ago.I swaped my 6:1 fmu out for a 8:1 two days ago so now i'm runing the 8:1.Everything that i stated is from what i have observed in my car and my friends cars with simular set-ups.