Hi,

I'm having this really weird situation for some time now. Being the noobie i am with fuel controllers, i increased the boost (psi) figure to 0.8 and 0.9. However i did not increase correspondingly boost duty? figures. What would the symptoms of incorrect boost setting? What happens now is when the car is about 1800 -2500 rpm i have hardly no power and the exhaust heat light flickers like mad until i ease of the pedal allowing gradual rev build up. Any comments or input much appreciated.

Dave

 

I have never used the built-in PFC boost controller, but I believe the left column of "BOOST + .2" is really the maximum boost before fuel cut, and the right column of duty cycle actually controls the boost.

What you did should not have caused any problems.

Let's hear from some of you that use the PFC boost control.

 

Here are two quotes from the PFC manual

"If boost level rises above .25 kg/cm2 over the preset boost levels, a fuel cut will occur"

"When using the factory pressure sensor, boost levels over 1.2 kg/cm2 cannot be accurately measured. For this reason, the PFC will illuminate the Exhaust Temp. Warning indicator for boost levels over 1.1 kg/cm2"

 

IIRC the left column is the boost pressure you want to hit say .85 or about 12.5psi and the right column is the duty cycle. you set the left column to what you want the boost to be and adjust the right column to achieve that boost pressure. its the same as setting boost up with an avc-r except you cant adjust by rpm.

this link, near the bottom of the page shows how this guy set up his boost with an avc-r: http://robrobinette.com/boost_avc_r_install.htm

for example:
· Turn the unit to setting [A] and again carefully apply power (you may hear the solenoid clicking - that's good), but stay below the 4500rpm for now. You should get close to 9psi... if not, increase the duty cycle a little (1-2%), retest, keep increasing until you get to 9psi. If you set the duty cycle too high, the controller will not be able to control boost, and will run higher than 9psi. For 9psi the duty cycle should be around 30%-40%. If the boost is not going above 7psi, there is a problem with the install. Recheck everything.

 

Just curious. . .wouldn't .85 kg/cm^2 be approx 12.09 PSI? Many times out here I see people using the conversion from atmospheres to PSI (ATM x 14.696=PSI) when the PFC reports boost in kg/cm^2 (kg/cm^2 x 14.223=PSI). I'm only mentioning this because it seems to be such a common mistake (if I'm wrong, please tell me!!). Even my (experienced) rx7 mech gave me the wrong info when I first got my PFC.

 

You're right...it's in kg/cm2. Watch the original PIM calibration though...the boost may not be accurate. At my alittude (3075') 0.89 kg/cm2 on the PFC = 15 psi on my boost gauge. Big discprepancy there. If you don't have a boost gauge and you may be running more boost than the PFC alludes to.

Just for some more info on the thread. As was stated the proper way is to choose your target boost then adjust the duty cycle to get there. I have noticed though if you change the target boost setting the actual boost will change without even touching the duty cycle.

 

not to get to far off topic here, but I have a question about the PFC readout and the gauge comparison.

My PFC says I'm running 0.7 (kg/cm^2)~10psi but my gauge reads .8 BAR which I know is aroung 13psi. Which one is giving me the correct readout?? Its a cheap mechanical boost gauge, which actually came with the car and I just havn't changed it out yet. And before the install of the PFC it read about .68 Bar.

 

The PFC reads low with default settings. Your other boost guage is probably more accurate. Changing some PFC settings (Datalogit required) can make the PFC boost reading accurate but may mess up your current tune. Here is a thread that talks about making the boost guage accurate and adjusting for elevation but has a lot of useless info to wade through...

https://www.rx7club.com/power-fc-forum-47/barometric-stock-2-bar-sensor-does-work-466783/

Many people don't realize their PFC boost reading is off but it won't cause a problem if they are tuned this way. Also 10000 kg/m^2 (absolute) is 0 psi (relative) at 910 feet and at sea level 10332 kg/m^2 (absolute) is 0 psi (relative). Not many people are capable of doing the conversions let alone understanding the principals of adjusting for elevation. At low elevation it's not much of a problem but it's surprising more people don't pop their motors at high elevation.

 

Thanks alot, and I do understand the whole elevation thing as I had to do all that stuff in college. So what you are pretty much saying is my boost gauge is probably right and I just need to turn my PFC setting down to compensate for its reading.

 

Yes, The default data relating to pressure in the PFC is not very good at any altitude from what I've seen. It is worse at high elevations and high boost. Trust whatever boost guage you have over the PFC boost unless you correct it.