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Discussion Starter · #1 ·
I was hoping that someone could tell me how to identufy the ratio of a vortech FMU. I found one in mint condition at a alocal pawn shop, but the owner has no idea what ratio it is. Is it written on the disk inside or something?
 

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hmmm I would think it is but you can always buy it and take it back if it's not what you want! all I know is that mines a 12:1 cause I bought it like that!
 

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im not exactly sure how to tell. i think there is a little deal printed on the inside diaphragm deal. if you found it in a pawnshop its probably not a bad idea to get a new disk. that way you konw its good and the exact ratio.
 

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Discussion Starter · #4 ·
Hmm...yeah that is probably good advice...better to spend an extra couple bucks than use the wrong equipment and break something later.

Thanks guys
 

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when i was using an fmu the disk would stick everyonce in a while when i first started using it.

but ya,, a new disk is relatively in expensive in retrospect. and worth it in the end. you can never really trust used stuff.
 

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Do you have a fuel pressure guage? Hook up the FMU with the vacuum port hooked to an air tank, start the car. Use an air tank to pump 3psi into it. Watch what your fuel pressure jumps to.

3psi Fuel pressure - idle fuel pressure / 3psi = your ratio

for examply I have an adjustable FMU.

At 4psi fuel pressure = 60
At 0psi fuel pressure = 20

60-20 / 4 = 10 I'm running about 10:1

This is pretty crude but it's the only way I could think to test it without running risk to leaning it out if the FMU wasn't working. ATI procharger verified that this is the only real way to test the unit is working without running the car boosted.
 

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fmu's dont work like their suposed to . mine was a 12:1 and it only did about 5psi increase for 3 psi boost. then any omre than that and it was arround 4 per psi......even with a new disk. thats why there so unreliable
 

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Marclar, you're only running 4:1 with 10+psi? Your injectors must be huge. When you're idleing are you runnig very very rich? I'm at 19psi on the fuel rail at idle with 24# injectors. I can't lower the rail pressure below 19psi but luckly the A/F guage shows that it's dead on with 24# injectors.

I'm assuming with that new megasquirt II system you don't need an FMU etc.... I bet that was a ton of work, I was reading up on the site and it seems very very involved.
 
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