The PowerFC is a popular ECU for MR2's however a lot of the original documentation is in Japanese and it's also quite an old system. This combination means that details about how it should work and how it actually work do not match up and it's no longer possible to 'ring the guy who made it'.
I'm looking in to boost control on the PFC at the moment and I recently found an article about it written on an RX7 website. The topic is generic enough that their observations and conclusions translate over to our (non-rotary) MR2 platform. From other things that I have read, this information looks credible so I wanted to repost a subset of it here that refers specifically to PowerFC boost control:
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Tuning Boost on the Power FC
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What We Know:
Pages 27 and 28 of the American Power FC manual have some instructions for tuning boost, and there is some info there, but there are as many open questions. Here is a summary of what seems to be clear:
* There are two sets of boost settings.
* Each has settings for the primary and secondary turbos
* Each can set the target boost pressure in kg/cm2 and the "base duty"
* Target boost pressure can be set between 0.0 (is this true?) and 2.0 kg/cm2 But...
o very low settings can be made, but the lowest max boost levels are determined by the wastegate spring (about 0.5 kg/cm2 or 7 psi).
o the boost sensor cannot read above 1.2 kg/cm2 so the unit will illuminate the Exhaust Temp light when 1.1 kg/cm2 is seen.
* The set of values that are used is the set that you are on when you leave the menus
* The values change in real time, with your cursor.
* There is a boost limit fuel cut if the PFC senses boost 0.25kg/cm2 higher than the set limit.
* Transition between turbos is still 4,500 rpm.
* The manual claims that there is some form of self learning??.
The maps in the manual are:
1. Pr 0.80kg/cm2 56%
Sc 0.70kg/cm2 64%
2. Pr 0.90kg/cm2 62%
Sc 0.80kg/cm2 70%
Here Goes a Lot of Speculation:
The PFC uses the stock engine inputs, their maps, the configuration settings above, and some dynamic "learning" algorithms to control boost through the duty cycle of the wastegate. This is important because both the "boost level" and "base duty" in the boost setting page have to control the same thing - the duty cycles at any given time. The boost setting also controls fuel cut. When adjusting desired boost you should be adjusting both the desired level and the base duty values for best effect. The manual states this as well, but is not clear on how to do this.
If you adjust for a lower boost level and do not lower the base duty then you can get the fuel cut! I was told (have no confirmation) that fuel cut in the PFC is actually ignition cut - so it may be safer, but it is still not good. If you have a base duty number that is too low, you will probably not get the desired boost levels consistently, if at all.
In my car I found it best to extrapolate from the settings in the manual, with about 6% base duty for each 0.10 of boost. When I had lowered boost by 0.10 or more without lowering base duty I would get fuel cut on transition in cold weather. YMMV.
That's about it:
* Set your target boost numbers, perhaps with secondary about 0.10 to 0.05 lower than primary.
* Set your base duty at an extrapolated number or lower, with secondary about 8% higher than primary.
* If you are not seeing the boost levels you want, slowly increase base duty cycles.
* If you are getting fuel cut, lower the Base duty cycles, or increase boost - pay attention to the transition point.
* If you are not able to get target boost, regardless of either setting, then there probably is something 'off' either with an input to the PFC (sensors) or with your turbo control system - but this is a strong statement - there simply isn't enough evidence.
* It's probably also important to have stock pills or close too.
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Mysteries:
* What is the nature of the "self learning" function? There is also baffling talk of a "self learning value". Is the learning just a real-time dynamic compensation, or is it more persistent, and is there a learning period like the PMC?
* What really is "Base Duty"?
As always - be super careful tuning and ECU - since it can blow up your engine.
As always - be super careful while testing your vehicle!!
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Retrieved 2/2/10 -
www.fd3s.net/power_fc_install.html
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