I was just wondering if anyone had any hints with regard to keeping the car in closed loop in boost so that I can view the fuel trims.

I seem to have a difficult time staying in closed loop for some reason while boosting. Is there a particular throttle percentage I want to stay below, or are there are factors besides throttle position I have to be aware of to remain in closed loop?

Thanks!

Yeah, i have the same prob too, esp after like 5 psi or so. I'm not too worried about it though, as ignition timing goes down as soon as it sees boost, and if i know i have enough fuel at WOT full boost, then part throttle boost should have plenty of fuel.

i've always had some weird issues in partial boost and partial throttle. when i'm at like 40% throttle and the turbo is spooling around 3000 rpm's, boost can get upwards of 8-10 psi and the oxygen sensor voltage will indicate an extremely lean condition. however, the instant that i give it more than 80% throttle, the power surges and it goes into the green with about .93 for oxygen sensor voltage. so i definately know that i have enough fuel pressure. it's REALLY annoying, especially when i see it in the red with the blinky autometer gauge at 10 psi at part throttle, then the ECU decides to go back and forth after a few seconds of being excessively lean. i wish there was a way to force the ECU to go into open loop the second boost is achieved...

i wish
>there was a way to force the ECU to go into open loop the
>second boost is achieved...

In fact, the J & S Safeguard has this very ability. Once the Safeguard computer reads boost, it will alter the TPS voltage so that it goes to 5v or 100%. That way, it will immiediately force the stock ECU into open loop mode.


"7) If the unit is connected to the TPS wire, the unit will pull the TPS signal to 5v at 0 psi. This should kick the ECU out of closed loop operation."

http://www.jandssafeguard.com/SubaruInstall.html

I have the opposite problem, obviously. I guess I have to mess with my car more. To me, it just seems that there might be more to merely the TPS going above a certain percentage which forces the car into open loop mode as well. I'm pretty sure the other day, while I was able to initially get the car into closed loop at partial throttle boost, later on, I was totally unsuccessful.

I think its probably the calculated load that determines when the ECU goes into open loop.

As for forcing the ECU into open loop when you reach boost. I was working on this recently. I worked out a design to do this, but put it on the back burner. I'll probably look into it again whenever I start running decent boost (kind of pointless if you run 6 psi).

Corbin

'95 ESI-T
HRC+FMIC+ETC...



Gimme fuel...Gimme fire...Gimme that which I desire

Well how about 18 corbin....lol where is this burner anyway....

I've been working on this. The ecu goes into open loop at 3.8v anything below that is closed loop. So you need a sensor that reads 0 boost. Corbin's sensor works great. At 0 boost it reads 1.6v. you need a switch that switches on at 1.6v and supplys 3.8v or greater but no more than 5v to the TPS ECU wire. The switch I used is www.autospeed.com/cms/A_1052/article.html with mods. to the switch it will turn on at 1.6v an supply 3.8v. I have got it built and it works great. :D

so right now you are using Corbins fooling afc mod AND this exact sensor you linked us to? or just use one or the other? also what do you have to 'mod'?? or do you just hook it up the way the website/directions tell you to? let us know what you did so it stays in close loop mode so we can tune for boosted operations easier.
the only way i can stay in close loop mode to read fuel trims is to go in a up hill or what not from a stop and floor it or step on it a bit to get it to the boost level i want to read fuel trims. but i dont get a very good look maybe few seconds.
anyways let us know.

"I've been working on this. The ecu goes into open loop at 3.8v anything below that is closed loop. So you need a sensor that reads 0 boost. Corbin's sensor works great. At 0 boost it reads 1.6v. you need a switch that switches on at 1.6v and supplys 3.8v or greater but no more than 5v to the TPS ECU wire. The switch I used is www.autospeed.com/cms/A_1052/article.html with mods. to the switch it will turn on at 1.6v an supply 3.8v. I have got it built and it works great. "

Michael 99gs 8-Injector Setup
HRC Stage 2 @12psi :D
Stage 3 process begins 2 months about till im built. hehe
2GNT Member #32

http://www.dreamwater.net/purplebeast

Yes tim, more information please!

Nick
97RS

That sounds like a great invention! The only thing i can see as a drawback to open loop right when you reach boost, is low boost/rpm power. If you are lightly boosting(0-5 psi), and you force the ECU into open loop, the ecu isnt controlling the A/F mixture anymore, which will now make you run from Stoic, to most likely rich, unless you have really good ways to control A/F ratio under light boost. Thats one thing i like about part throttle boosting in closed loop, is that the ECU is trying to make the best A/F ratio for good power and economy, which should keep the motor fairly peppy under light boost, esp since the timing advance goes down immediatly under boost... I just think it would give a slight null in power, but thats just guessing anyway..Now if you can throw the ECU into open loop like Corbin has mentioned, like at 6 psi, then that would be perfect IMO

You use both sensors. Corbin's sensor sends an output to the "warning" sensor. Based on what "warning" sensor is set at it closes the circuit and trips the relay. The input voltage of the relay is the MAP sensor power wire. The voltage is step down by using a resistor. You can set it to go in to open at any boost level. Just boost and record the voltage that comes out of Corbin's sensor and set the "warning" sensor at that voltage by turning the 2 pots. For more info on corbin's sensor go to Fooling the AFC. Hope this helps. More details later. }(

Im sorry maybe you guys can help me understand more. What you are trying to occomplish is to trick the ECU into open loop. Which will give you full stoich at partial throttle. This way it insures that you have enough fuel at partial throttle?

Am I understanding this correctly?

Nick
97RS

Aww man...I wish I knew about that warning circuit. I was trying to build this thing from scratch. I just read through my old electronics text books and started digging through the Motorola and National Semiconductor web sites. Talk about a PITA. I was planning to have the unit kick into open loop as you hit 4-5 psi. The car performs nicely in closed loop at low boost.

I think the point is to give yourself full control over the fuel at higher boost pressures (despite throttle position). Then you can run however lean or rich you want without the ECU messing with things. Plus, you get alot of timing advance at part throttle which may disagree with higher boost pressures. If you run in closed loop at higher boost pressures, the ECU will adjust fuel pretty lean and keep the advance high. You will quickly break 1600F on the EGT (not desirable).

Corbin

'95 ESI-T
HRC+FMIC+ETC...



Gimme fuel...Gimme fire...Gimme that which I desire

How many of you datalogging guys watch igniton advance under boost? I know mine goes down to 17-19 degrees as SOON as i hit boost, like 0 psi, and on up. I have datalogged my 98, as well as Matt_95tgs's 95, and both were the same way..The advance still goes down in low boost, regardless of open or closed loop operation.

Hmmm...I'm going to have to check my car out. I thought it kept the advance in closed loop boost. If it knocks the timing back as soon as you break 0 psi, then an "open loop boost mod" isn't that useful. It would only really help you from running too lean in closed loop boost.

Corbin

'95 ESI-T
HRC+FMIC+ETC...



Gimme fuel...Gimme fire...Gimme that which I desire

Anything else come of this? I have been thinking about this a lot recently. It seems like my egt's shoot up quick in closed loop / partial throttle. At WOT they stick at about 1450-1500. This makes me think that the ecu is advancing the timing but the turbo is building boost that is making it way past the throttle plate. timing advance and boost = high egt's. Mabye if we make the thing tell the TPS its at like 75% or whatever the max is on our cars it will retard the timing as it starts to build boost. Mabye im way off base, but mabye thats the way to go?

I'll concede...looks like the ECU retards timing as you break 0 psi. I was getting 14-17 degrees while boosting in closed loop. I could get it to change based on throttle position. So, there's not much reason to worry about excess advance at part throttle boost.

Corbin

'95 ESI-T
HRC+FMIC+ETC...



Gimme fuel...Gimme fire...Gimme that which I desire