Jeep98cherokee

The way that I was told that you can tune the fmu is with a mbc. You just put it on the boost line to the fmu. Then watch the afr. Have any of you heard of doing it this way? I know it's not the right way but will it work? Thanks for the input.

Jeep98cherokee

Yes I have a fuel cut defender for the map. And I'm running a return line to the tank with a 94 fuel rail. It has the return line.

donnie m

I think the only reason you want to run a fmu is so you dont burnout your stock fuel pump or starve the injectors. I agree with busa4 its a shotty way to get more fuel to the motor, your just basically forcing more fuel in the rail at higher pressures under boost. It will work but read what busa4 said. A better way is to use a map control module like the split sec psc-001 or something programmable that reads boost and larger injectors. It will do the same but safely. Your already using a walbro255 so fuel delivery shouldnt be an issue.

Jeep98cherokee

the split sec psc-001 dose that tap in to the map or ecu? Dose any one know what injectors I can get form the junk yard? The jeep comes with 19p injectors form jeep. Thanks for all of you helping me.

busa4

the mbc will only change the ratio of fuel pressure to boost. how it works is the mbc will vent a specific amount of boost to the fmu changing its ratio.

example: if the mbc is opened up most of the way then the fmu will have little rising rate such as 2:1(every psi boost fuel pressure will raise 2 psi)

if the mbc is closed most of the way then the fmu will have a larger rising rate such as 10:1 (every psi boost fuel pressure will raise 10 psi).

the rising ratio cannot be adjusted to different ratios at different rpms or boost so it will cause lean spots and rich spots in different rpm ranges so an fmu is not recommended.

please get the fmu idea out of your head. im trying to save you the trouble and your engine.

busa4

they have two types.
the psc-001 taps into the map signal

the psc-003 tamps into the maf signal

these units modifiy sensor signals sent to the ecm. i personally dont like these types of controllers as they are limited in adjustment.

these two extra injector controllers i would recommend. they allow you to use your stock fuel system and stock ecm tune
http://www.autopartsdealer.com/sard_..._content=rank1


Underdog Racing Development

Jeep98cherokee

I like the face. If I go with that I do not have to do any mods to the stock fuel set up? Just add the injectors and use the face to get the afr right. Can I use any injectors? How do you get fuel to them?
What about timing? Can I use the Msd Btm?
Thanks for the help.

busa4

the one with the adjustments on the face is for use with low impedence injectors. the controller mounts in your cab and you adjust the parameters from there.

the one for sale by underdog uses high impedence injectors. this one requires a laptop to program with the supplied software. it uses a 3d map based on tps, rpm and boost pressure. it can control up to 6 high impedence injectors. this is the one i am using.


these are just the controllers so you will need to purchase injectors, fuel rail and line to finish. these do not control timing. there should be no timing adjustment needed for 10psi boost or less. these are great because you use your stock fuel system, injectors, and stock tune so there are no issues with driveability and emissions.

injector size selection is based on how much hp over stock you are looking for. you should have a shrader valve on your stock fuel rail you can tap off of.

Jeep98cherokee

Were do I get the injector rail at or do I make one? What is high and low impedence injectors?

Jeep98cherokee

busa4 thank you for your in put. Do you have part numbers form your face kit?