Stay away from FMUs. FMUs will give you no extra power. At most they are a cover and will get you nowhere. They are bad!
If they are bad , then EVERY tuner that uses them is incorrect. And that's quite a lot. Actually , if you think about it , FMUs are NOT bad , in fact it could be the very thing that saves your engine. FMUs prevent too much fuel from being recirculated back to the tank , and much above a low level tuned car that could result in a lean condition. It also helps raise the fuel injectors capacity a bit , which is also not a bad thing if you are running close to the limit.
James , I know you got that information from Z31.com , but the more I read from that place , the more I'm convinced those guys have no clue what they are talking about. For example , DSM tuners have been using rising rate FMUs for years. DSM tuners are also running 8s on the stock ECUs on 30+ lbs of boost , which is quite far outside the stock ECUs operating range. If you use the proper equipment , you can get a car to do anything you want.
Let me iterate a few things , before James thinks I'm picking on him. FMUs are useful in a number of ways. #1: They can prevent a lean condition caused by hi flow large turbos that run at fairly low psi , since the stock FMU responds directly to the psi/vacuum present in the intake manifold , or the equivalent location. #2: The extra few psi of fuel pressure gives the injectors that extra "kick" , and through the O2 sensor can actually cause the ECU to close down the pulse width a bit. This is not a bad thing #3: It allows high rpm turbo cars to run deeper into the redzone without the risk of leanout associated with the typical loss of boost pressure at extreme rpms.
FMUs are fairly useless by themselves , except as in the case of #2. A typical stock FMU/FPR cannot handle the associated increased pressures resulting from increased boost pressure over stock , or even a higher pressure fuel pump. This typically results in what every tuner knows as FPR overrun , and in extreme cases can cause FPR failure and a resulting leanout condition , which WILL seriously damage your engine , especially if you are deep in the heart of the power band at high rpms. Can you say melted pistons?
FMUs are typically coupled with such devices as Super-AFCs and VPCs , and is a very useful tuning tool. Typical stock ECUs reduce timing after seeing a certain amount of airflow (either lbs/hr or cfm) , but using a S-AFC combined with massive injectors and an FMU can cause the ECU to actually ADVANCE timing , as the S-AFC tricks it into thinking it's seeing LESS airflow than is actually going into the engine , while maintaining fuel flow capacity. I've seen timing advances of better than 40 degrees in DSM applications using the devices listed above. Timing advance is a good thing.
As I've been trying to explain , FMUs are a part of the whole picture and not very useful by themselves. But used correctly they are an extremely useful tuning tool. Ask any tuner in the 10s or 9s in the 1/4 , he likely has one.
Last edited by B@lliZtiK : Mar 26th, 2004 at 06:37 AM.
Right so a simple answer to our question is Fuel Management Unit- Like my super afc- I'll tell you what, from experience they do work and it is an extremly useful tuning tool when used in the right application.- I used it with nitrous on my nx and Im going to use it on my Z when I start making more boost- Is a fuel pressure regulator really worth it though? I seriously think I need to replace mine- my fuel pressure at idle yesterday was 29 - is that right? I need to order the factory service manual
__________________ ONE OF THESE DAYS I'LL FIGURE OUT HOW TO CHANGE MY WIPER BLADES
Right so a simple answer to our question is Fuel Management Unit- Like my super afc- I'll tell you what, from experience they do work and it is an extremly useful tuning tool when used in the right application.- I used it with nitrous on my nx and Im going to use it on my Z when I start making more boost- Is a fuel pressure regulator really worth it though? I seriously think I need to replace mine- my fuel pressure at idle yesterday was 29 - is that right? I need to order the factory service manual
29 is a bit low. Typical is in the 40s , and deadhead pressure (With the FPR fully closed) should be about 60-65 psi. I'd hook up a pressure guage to the accessory fitting on the injector rail (the pressure release fitting) and blip the throttle a few times and see what happens. If it (fuel pressure) spikes higher right as you blip the throttle its likely good , if it drops as you blip the throttle it's likely bad.
FMU is just a fancy name for an aftermarket FPR , its not to be confused with a complicated unit like a S-AFC.
Last edited by B@lliZtiK : Mar 26th, 2004 at 07:29 AM.
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