FMU help

[Drew]

I bought an FMU off of ebay and I was told it is a 6:1 ratio. When it arrived today I noticed 12:1 stamped on the bottom. How can I tell what ratio it is? By the size of the hole in the plate inside or what?

[Shane]

the 12:1 dis is 2.75 inches across.....if its smaller then that then it prolly is the 6:1.....take a pic of it in the FMU and I can tell you.

[Tiago]

or use a fuel pressure gauge and put some pressure to it and see how much it raises and calculate.

[Drew]

Well I found out that it is a 12:1 ratio, not 6:1 as I was told :mad: . Anyways, on a 3.4, how far can I push the stock injectors with a 12:1 ratio fmu, and will I run ok?

[T-Punk]

probably not, 12:1 is a huge ratio

[Shane]

toooooo much

[Drew]

Is there a way I can make it a smaller ratio without a recalibration disc. I think I read something about a bleeder valve?

[98GREENGLOW]

You can basicly just cut the tube that goes from the throttle body about 6 inches before the FMU and insert a 3 T connecter. Hook two sides of the 3T connecter into the two lines that you just cut,making them basicly be put back together. Then for the third end of the 3T connector, Put about 3-6 inches of tube and at the end of the tube put eighter a pvc valve or a plastic air bleeder that you can buy from any fish store.

The idea is that the air pressure or boost is sent from your FI system through the tubing to the fmu. The FMU then says Hey...That FI system is making 6 pounds of boost so Im gonna x that by 12 and add an additional 72 pounds of fuel to the 50 or so he already has....Resulting in you running WAYYYYY RICH.

With the pcv valve or air bleeder the air goes from the FI system through the tubing just like before....The only difference is that theres a detour about 6 inches before the boost hits the FMU. Some of the boost will escape through the pcv valve or air bleeder before it hits the FMU... Causing the FMU to be fooled and beleave that your FI sytem is only making 3 pounds when it's really making 6 pounds. So then instead of the FMU adding an additional 72 pounds at 6 pounds of boost it will only add an additional 36 pounds at 6 pounds of boost thanks to the detour you created.

This method helped my fuel pressure go from 100+ to a pretty constant 70 under full boost.

[Drew]

How do I know what the fmu is reading boost wise using my fish air valve so I can know how much vaccum line to run?

[98GREENGLOW]

You need a fuel pressure guage to be able to see what fuel pressure your running.

Then you just experiment with the fish air guage having it barely open and doing a full boost run. If it's still too rich then open the fish air valve a little more and repeat the process till your at the full pressure level you desire.

The more you open the valve....The more the air will escape......The more air that escapes.....The less boost the FMU will read.....The less the FMU reads....The less fuel it will generate.

It's pretty easy to hook up and try out. You can buy the pcv or fish valve easily for under 5 bucks and then hook it up in two minutes.

[Drew]

Question: So, I'm purposely venting air out of my system here to trick the FMU. Am I also tricking my boost gauge? All the vaccum lines use the same air, so I'd think the gauge would read low

[98GREENGLOW]

NO, it dosent interfere with the boost guage. At least not on my set up.