Fmu?

[BIGSHOMIKE]

I see alot of posts about bigger injectors (for forced induction), I was talking with a local tuner, he says they use stock (size) injectors with a FMU to boost pressure, during boost only, which they believe makes them esiar to tune?

Just wanted to get some input on this.

Thanks

 

[SHOnuff93]

The FMU is a bandaid fix and is usually used on cars without a return type fuel system. The proper way to tune the car (not the easiest but safest) is to upgrade the fuel system to handle the extra air entering the engine and then re-map the fuel curves appropriately.

 

[RStalveyARFF]

Not to mention, the stock injectors max out around 300hp

 

[SHO Dude]

FMU's are a terrible way to tune. They artificially increase fuel pressure based on boost pressure. The problem is that fuel flow does not increase with fuel pressure in a linear fashion. You can double the fuel pressure, but it'll only get you about 30% more fuel.

I prefer to install the biggest injectors possible, then plug in the right tuning factors into my SCT tuning and everything works like it should. Case in point; the last blower car that we delivered idled perfect with 42lb injectors and got 25mpg from Atlanta to Myrtle Beach. It puts 325hp on the ground with only 8 1/2 psi of boost.

 

[somedude_001]

after searching I think I have found the information I need but I just want to be 100% sure and I htink this is the proper thread to bring back for this question.

my friend turboed his 3rd gen eclips and he said he had a FMU laying around that I could use on my turbo project this winter but i'm not so sure I need one, I understand how the FMU works and what its soposto do but why woud I need one?

i'm using a 190LPH pump, 44lb injectors, tweecer, and still need to purchase a larger maf and FPR, now how is the computer going to know there is boost and how much? I don't really see why the computer would need to know that there is boost because it knows how many CFM is comming in (via the maf) so won't it compensate by adding more fuel? is there any reason to run a FMU on a setup like the SHO has? and FYI i'm planning on 9psi to start and I will see how long my ATX tranny lasts.

 

[Silver95]

FMU's are a terrible way to tune. They artificially increase fuel pressure based on boost pressure. The problem is that fuel flow does not increase with fuel pressure in a linear fashion. You can double the fuel pressure, but it'll only get you about 30% more fuel.

I prefer to install the biggest injectors possible, then plug in the right tuning factors into my SCT tuning and everything works like it should. Case in point; the last blower car that we delivered idled perfect with 42lb injectors and got 25mpg from Atlanta to Myrtle Beach. It puts 325hp on the ground with only 8 1/2 psi of boost.

Thats not bad at all for 8psi of boost. What mods were on the car before boost? 3.0-3.2?

 

[Toolman]

I understand how the FMU works and what its soposto do but why woud I need one?

If you tune the car for the larger injectors you will not need one.

i'm using a 190LPH pump, 44lb injectors, tweecer, and still need to purchase a larger maf and FPR, now how is the computer going to know there is boost and how much? I don't really see why the computer would need to know that there is boost because it knows how many CFM is comming in (via the maf) so won't it compensate by adding more fuel? is there any reason to run a FMU on a setup like the SHO has? and FYI i'm planning on 9psi to start and I will see how long my ATX tranny lasts.

No, there is not a reason to run an FMU. Get a Tweecer or other suitable tuning device and leave the FMU alone.

 

[somedude_001]

thankyou

 

[SonicRiot]

A little help:

What does FMU stand for?

Thanks for helpin' the nube!

 

[NotSoSlowSHO]

Fuel Management Unit

 

[SonicRiot]

Thanks for clearing that up. Too many acronyms and stuff to keep up with!

Is it a stand alone fuel management system?

 

[Off Road SHO]

Thanks for clearing that up. Too many acronyms and stuff to keep up with!

Is it a stand alone fuel management system?

Well, yes it is, in its own way. Just like the computer manages the amount of fuel the injectors squirt on an advanced system like ours, the stand alone FMU does it the old barbaric way: vacuum goes down, increase fuel pressure.

Tom

 

[SonicRiot]

Gotcha. Poor method of tuning. Thanks for the info.