Cartech FMU problem

[speed_addict]

Hey guys, I've got a 98 GS400 that's been giving me problems ever since I had the RMM supercharger installed by a shop. I've been going through a bunch of problems and finally got almost all of them licked...except for the Cartech FMU. I was getting a misfire on cylinders 1,3,5,7 and a p0100 error. Tracked it down to the FMU. With the vacuum unplugged on the FMU my fuel pressure is between 40-45psi car idles perfect, no codes. When the vacuum is plugged in to the Cartech FMU, the fuel pressure goes down to 20 psi and I start getting all those codes. Leads me to believe the fuel pump is good, the injectors are good....any thoughts? I've been fighting with this for the past month. I'm only able to work on the car on weekends. Thanks for your help.

the setup is:

RMM supercharger
Cartech FMU
Split second ESC-1
Snow methanol injection
custom headers
walbro intank pump
AEM wideband
stock injectors (yea I know...I supplied RC 440's but they didn't install them...they are too big )

car netted 396 whp and 337 tq on a hot TX day.

 

[spf_lexus]

Is your FMU adjustable? Most should at least have an adjustment knob on board to dial in idle fuel pressure. You would need a fuel press. gauge to tell where your at.

 

[speed_addict]

its adjustable. you can adjust the FMU without the vacuum plugged. Its adjusted at 40 psi on idle. I've got a gauge. but when I plug the vacuum on the fmu in, psi drops to 20 psi with no adjustment availabe on the fmu.

 

[Spinall4]

Ditch the FMU and get real fuel control. Replace the FMU with a good 1:1 rising rate regulator.

Sounds like the diaphragm inside the FMU may be torn.

 

[viper92086]

should you be running a check valve so that the fmu doesnt see vaccum only boost?

 

[speed_addict]

I had a checkvalve on mine. I believe cartech recommends it. I bypassed the fmu and the car runs much better, still has a code but is running now.

 

[spf_lexus]

I have a Synapse FMU and it has a port for vacuum and boost that are separate. $200 w/o issues so far. Made for honda's but with a fitting or 2 works great.

 

[stevechumo]

I had a checkvalve on mine. I believe cartech recommends it. I bypassed the fmu and the car runs much better, still has a code but is running now.

Make sure you don't run lean under boost. I usually run the fixed rising rate 12:1 FMU with a hf-hp 255 fuel pump and never had a problem unless I went passed 8 psi.