dr_jones

iTrader: (1)

Anyone know what the reason for using a 3 port solenoid over a 2 port is?

Also the 2 port (as on mine) - does it's operational frequency get controlled by the ecu to intelligently controll boost or not?

Any info would be much apreciated....

john banks

Yes the 2 port is closed controlled loop, on MY99/00 based on four levels of boost error of 0.3, 0.7, 1.7 and 3 PSI from target based on RPM and throttle position. There are four rows to the table for short term errors above and below and long term errors above and below. The lookup in the table is a ramp rate to increase or decrease between the maximum and minimum duty cycle (fixed freq about 15 Hz) for that zone based on RPM and TPS.

The 2 port does not flow enough to remove significant pressure from the diaphragm so there is a restrictor. As such it has a narrow control bandwidth.

The 3 port allows much greater flow, and sits so that it can totally block the boost pressure from the diaphragm in the high parts of the duty cycle (mark) and flow most of it in the low parts (space) of the duty cycle. As such it provides a wider control bandwidth and is more precise.

Sadly the 2 port system does not achieve target boost in every gear without significant peaks which vary depending on EGT and other operating conditions.

Newer Denso ECUs have more compensations available for other variables, some can use temp comp, gear comp and integration, although a lot of the features are disabled.

I run a nice system on my ECU which allows the defunct intake air temperature maximum duty cycle compensation to be varied by acceleration rather than IAT, hence a nice gear judge, so you can get full boost in every gear, even first if you want, without massive peaks even in 5th gear.

The standard system depends a lot for its control based on maximum duty cycle for each zone, which really determines either whether the ECU will even hit target, or what degree of initial overboost you will get.

Overall, quite a clever system, but you have to give it all the right numbers to work with.

Bob Rawle

'97 STi is a STi 3, that should have a VF23 turbo, boost control solenoid is the early two port and is not like the later ones.

Same philosophy applies, three port is much more granular at controling boost but ... you need to map the ecu to take advantage of it, you can swap to one and then use restrictors of varying sizes to sort out the boost levels, the taper is probably mapped in though, frequency is fixed at between 10 and 15hz, usually ends up at 12hz, pulse width is varied to allow more or less pressure to operate the actuator and open and close the wastegate. The normal result if fitted to the car using std ecu and no restrictors is for boost to hold mapped targets solidly with no overboost at all.

dr_jones

iTrader: (1)

Cheers Bob - Will have a look at laying my hands on a 3-port to see what effects it may have.

For the mo' I've sourced a nice flow control valve so I'll see what difference I can make with the ususal resrictor size mods and my current 2-port will have as currently I'm still trying to unravel the mystery of the missing boost and seemingly inreased taper http://www.scoobynet.co.uk/bbs/threa...hreadID=181170 - maybe I had crap in my restictor all along

Bob Rawle

1.1 bar is what it should be, the car was obviously running ahead of its boost targets before and has now decided to run normally, the overboost is ok for as long as the timing will put up with it, if it had been detting when it was rolling roaded PE would have spotted it. You should really run booster with it as well. How did you reset the ecu ?

dr_jones

iTrader: (1)

Thats what I was beginning to wonder.

Reset the ECU by:

Plugged black to black + green to green under dash - ignition on - accelerator pedal down for a few seconds - drive for about five minutes (eng check light flashing at constant rate) - stop, unplug green + black connectors.

Bob Rawle

Try just disconnecting the battery for 30 mins just to make sure it was reset.

dr_jones

iTrader: (1)

OK - will give it a go and see what happens.

dr_jones

iTrader: (1)

Nah - no change at all - still 1.1 bar tapering from about 1.25 / 1.3ish - any idea if the ECU could have lost it's map? - or eve if this is possible?

ECU Details :http://www.scoobynet.co.uk/bbs/threa...hreadID=186196

rosswalker

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Bob Rawle

"still 1.1 bar tapering from about 1.25 / 1.3ish"

Thats as it should be, the 1.25/1.3 is actually over the top of the set map.

dr_jones

iTrader: (1)

Cheers John - I think I understand the control system a bit better now

From that am I right in saying:

A: without a different ECU there's no way I can got to a 3 port

B: There may be some mileage in using dual 2 port sols to enable a greater max flow from the actuator diag.?

BTW - it's a'97 Sti - trying still to control my boost taper

[Edited by dr_jones - 3/7/2003 6:41:20 PM]