blkdragteg63

whats up guys... recently my in-line fuel pump started to mess up. i have a 97 gsr with a drag 3 turbo kit on it. Currently i have the stock fuel pump with the in line fuel pump also. I talked to a few people and they said that i could just get a bigger intank fuel pump and get a fuel pressure regulator, and be rid of having 2 fuel pumps. Then someone told me that unless im using hondata i still have to keep an inline fuel pump and the fmu also. More or less using an aftermarket fuel pressure regulator and bigger in tank fuel pump is useless. Id like to get other peoples views on this. Will i be able to just use one big in tank fuel pump and a fpr and keep my fmu or is it pointless and im still going to have to use an in-line fuel pump? thanks guys....

inspyral

If you're using an FMU, you NEED an inline pump, period. A high-flow intank pump can flow large volumes, but it can't generate the high pressures at the rail that your FMU needs. If you're going to ditch the FMU setup, which is a good idea if you're running anything over about 8lbs of boost, then get an intank pump, larger injectors, and something to control them(Hondata, AFC, etc). If you're sticking with the FMU setup, get another inline pump.

blkdragteg63

so what is the purpose of having an fmu? right now im running about 8 psi

inspyral

The FMU raises fuel pressure dependent on boost pressure. Your FMU is most likely a 12:1, which means for every lb of boost, your fuel pressure goes up 12psi. That means that at 8lbs of boost, if we assume a 40psi base static fuel pressure, under full boost, your fuel pressure is around 136psi(8 x 12 + 40). This is a tremendous amount of pressure at the rail going thru your injectors. Even the best intank pump maxes out around 80psi, so if you try to run an FMU setup off just an intank, you will lean out under boost. As for a reason why you might want to get rid of the FMU setup, the high fuel pressures associated with them can cause injector failure, and if that happens under boost, you could potentially destroy your engine. FMU setups also tend to run excessively rich if you don't trim fuel under boost with an AFC or similar device, so you also lose power that way. If you plan on staying under 8lbs of boost, an FMU setup will probably be adequate, but if you decide to up the boost, I would not trust an FMU setup. The best option is always to use larger injectors with a standalone unit, but if you can't afford that and you don't plan on upping your boost level, then just get a new inline pump and be done with it.

blkdragteg63

i think im just going to get a new in line fuel pump and save up for all the stuff to run hondata.. i already got the in tank and a holley fpr, i know im still not even close but im just gonna get it little by little. All my friends that have hondata say its worth the money.. I know for hondata i have to convert my obd2 to obd1 and get the obd1 p72. is there any other ones that i can use that is compatable with obd2 that doesnt cost an arm and a leg?

blkdragteg63

If i go hondata or anything like that does that eliminate the need for the fmu, afc and all that other stuff?

inspyral

There aren't any standalone units that I'm aware of, that work with an OBD-II ECM, at least not the way Hondata works with the OBD-I ones. You can go with another unit like AEM EMS or Power FC, etc, and those will plug right in and work with OBD-II, but they replace the ECM altogether. Pretty much any standalone is going to cos a significant amount of money.

With a standalone, there is no need for a boost dependent FMU since you'll most likely use the standalone unit to control larger injectors that will handle your fueling needs. You don't need an AFC because you the standalone to control your fuel map.

blkdragteg63

is it worth changing it to hondata or the aem ems?

blkdragteg63

so if i just stay with 8 lbs and under its probally better to just replace the in line fuel pump... should i still get bigger injectors and an v afc to controller it?

inspyral

A standalone unit will always be your best option for tuning. Whether or not it's "worth it" would be entirely up to you. If you're going to stay at 8lbs of boost, and you don't really need to extract the most power out of your setup and have the best reliability, then you probably wouldn't need a standalone. In addition to the cost of a standalone unit, you'd have to factor in dyno time, and paying someone to tune it, unless you feel comfortable doing that yourself, and that adds a considerable amount to your final cost.

If you want to stick with the FMU setup, then get a new inline pump. If you want to run larger injectors, depending on what size injectors you choose, you may ditch the FMU altogether, or you may just step down the FMU ratio by changing the calibration disc. You can run injectors as large as about 310cc on your stock ECM, and you would probably want to use about a 8:1 disc in your FMU with them. If you go larger than 310cc, you won't be able to idle them with your ECU, so you'll need an AFC or other device to trim fuel to idle and run them properly.

If you already have an intank pump, I would put that in, and run some DSM 450cc injectors with an AFC. With this setup, you could ditch your FMU and you won't need an inline pump. You can also get rid of whatever check valves and such you may have bleeding boost from your MAP sensor, if you stay under 10-12lbs of boost, since you'll be trimming the MAP signal to the ECM via the AFC in order to idle and run the 450s. The DSM 450s can be had for about $50-80 depending on where you go, and sometimes you can get them for even less. You'll need a resistor box or inline resistors to run them since they're peak and hold, and you'll also need OBD-I injector clips. An AFC shouldn't cost more than $300 new, and probably $200 or less used. Once it's all together, you can run a conservative base timing retard, colder plugs gapped at about .031", and get it tuned. It'll run pretty reliably, especially compared to an FMU setup, and you should be able to tune your A/F curve pretty well. In the future, if you decide on a standalone, you can simply take out the AFC, put in the standalone, and you'll already have the larger injectors and intank pump.