ekk41

Modified by ekk41 at 6:23 PM 3/11/2008

0mtber

iTrader: (2)

What is an fmu?:
A Fuel Management Unit (FMU) is a special rising rate fuel pressure regulator placed in the fuel return line of the fuel injection system. This is a very common approach to handling the increased fuel demand required by turbo kits and supercharger kits. It does work. It will make the injectors flow more fuel than their rating. These are used in addition to the factory or aftermarket fuel pressure regulator and only have an affect under boost.
FMUS are rated by the ratio of fuel pressure to boost pressure. For instance, a 10:1 FMU will give you 100psi fuel pressure at 10 psi boost pressure.

Why you shouldn't run an fmu/missing link?:
Fmu's are considered a "hack" they overload your injectors with high fuel pressure to compensate for boost pressure. This is the improper solution for fuel management on a forced induction vehicle. Most stock engine computers do not retard timing under boost hence causing dangerous engine conditions. A missing link simply stops the manifold pressure sensor from seeing positive pressure, hence preventing a check engine light.

Why piggybacks (vafc, emanage) "suck" by pgmfi:
Piggy Back controllers allow stock ECUs to do things that they normally can't do, like run larger injectors or deal with boost. Remember that piggyback controllers work by altering sensor signals before they get to the ECU.
Most of the time, the primary signal being messed with is the Map Sensor. This is critically important in a Speed Density car. The Map Sensor is used by the ECU to guess how much air is going into the car, and therefore how much fuel to supply in order to match airflow. When you "lean" out a car with an AFC, you are simply decreasing the Map Sensor signal - the ECU responds to the decrease in manifold pressure by supplying less fuel. When you "richen" a car with an AFC, you are simply increasing the Map Sensor signal - the ECU responds to the increase in manifold pressure by supplying more fuel.
The change in fueling happens for a reason: if you look at a fuel table, Map Sensor values correspond with columns. When you increase or decrease the signal from the Map Sensor, you are simply making the ECU use a different column than it originally would have used. (see Understanding Maps if you need some help understanding reading Fuel and Ign tables)
But wait, isn't the Map Sensor used for determining ignition requirements too? When you "lean" out a car with a Piggy Back, you also in all likelyhood advanced timing. When you "richen" a car with a Piggy Back, you also in all likelyhood retarded timing. Look at trends horizontally (as MAP changes) in an ignition table, and you will see why this happens. This helps explain why so many boosted cars running on the "AFC hack" have issues due to excessive ignition advance.
The bottom line: Piggy Back Controllers suck because you cannot independently adjust fuel and ignition. Any changes to fueling will produce a change in ignition too, and often this is undesirable.

ekk41

Thank You for answering my question. I know this is off topic but is it safe to run without a Fuel Pump and a Fuel Pressure Regulator for the time being? I'm only going to be boosting 7lbs until then.
And heres my set up Bone Stock d16y7
14b Turbo I believe its off the Greddy Kit Barely any shaft play if any
Precision 440s or DSM 450s
FMIC 28"x6"x2.5"
My RevHard Dseries Log Manifold or an OBX / SS autocrome manifold
Some cheap BOV
38mm Tial Wastegate
Vortech FMU

This is a cheap set up but hey i picked it up for 200 bucks

I figured I just wanna have fun with it for now. If anyone saw my turbo set up before it was but like a month ago I ran into some problems financial debts =[ so I had to sell it and i was a 1000 short for tuning clutch ecu /w obd1 conversion harness and chipping and tuning. And i came across this for only 200 so hey why not.

blinx9900

i say this all the time, for sohc's fmu+fuel pump for anything around 10psi. yes a tuned motor will be faster, but with such low comression you dont really have to worry about timing too much imo. if you have the money for a better option i suggest you do it if not, fmu is ok too. safc is just a no no to me.

Chris Tune

FMU FTW?

Schister66

With how cheap chipped ECUs are and with the availability of capable tuners, there's no reason to get anything else if you want your setup to make as much power as possible (safely) and last for a while. People always try to cut corners when picking an EMS and ironically, its the MOST important part of the whole setup

adseguy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Schister66 &raquo;</TD></TR><TR><TD CLASS="quote">With how cheap chipped ECUs are and with the availability of capable tuners, there's no reason to get anything else if you want your setup to make as much power as possible (safely) and last for a while. People always try to cut corners when picking an EMS and ironically, its the MOST important part of the whole setup</TD></TR></TABLE>

Agreed. And here's the worst part on HT: People dont' realize how cheap and easy of a solution a chipped ECU is on the honda platform. I really think that no other car has such a cheap and GOOD solution out there. Normally if you want it done right you literally spend thousands of dollars going stand alone, not to mention the headaches of setting up the wiring and then troubleshooting everything. IMO even the tune isn't as good as a neptune since it's hard to really dial in the idle, ECT temp correction, IAT correction, etc. These things would need to be tuned over a period of a year to finally get it right. I used to deal with AEM, but now i don't on Hondas because of the obvious other choices that ROCK! So for a paltry $30 to chip your own ECU and then you would have had to pay for a tune on any other car at 300 some dollars, you are done WITH a quality tune (hopefully with a good tuner)

Soo.....stop whining about whether to save $50 and go FMU or have an EXCELLENT setup for an extra $50

ekk41

You guys have forgotten that I would need to go obd1 which means p28? runs about 100 - 150 and then a harness which runs about 50 bucks + getting it chipped would be 75 bucks + 150 an hour tunning but you have to get it tuned for 2 hours so that would run me about... any where from about 500 - 600 + on top of that i would also still need a Fuel pump (100) fuel pressure regulator ( 70 - 100) and a clutch (300) with that saying its like if i get it tuned spending about 500 might as well wait it out and complete everything else . All i wanted to know was is it safe to run a fmu only at 7psi without a fuel pump and a fuel pressure regulator for the time being

ekk41

Thanks for all the input really appreciate it

0mtber

iTrader: (2)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ekk41 &raquo;</TD></TR><TR><TD CLASS="quote"> All i wanted to know was is it safe to run a fmu only at 7psi without a fuel pump and a fuel pressure regulator for the time being</TD></TR></TABLE>

The answer is no. Do it right or don't do it at all :-)