Taking the brave/stupid route. building a FCD.

[IggDawg]

My recent issues have made me want to go ahead and build a FCD. I don't hit above 13 lbs (or even 11lbs for that matter) except in momentary spikes. But the single momentary lurch is ugly and certainly undesirable. very disenchanting. So I want a FCD. I'm going to go ahead and build the one Morgie gave reference to here:

http://www.teamfc3s.org/info/articles/fcd/diy_fcd.htm

anyone know what voltages our MAP sees? I'm assuming that's what I'm going to be hooking it up to.

[boostjunkie]

I'm still wondering why my fcd isn't even tied into the MAP sensor yet I'm not hitting fuel cut. Lemme try taking the thing completely out of the system. I might be able to sell you my HKS unit if your homemade fcd doesn't work.

[IggDawg]

Hi . jsut saw you on NASIOC in teh JoeP FS thread .

out of curiosity, where doe it hook in?

[boostjunkie]

To be honest, I don't know. It was already installed on the car when i got it. But, there's a MBC installation instruction guide on DLC's site. Same setup with the Joe-P.

Yeah, I saw your post in the classifieds and was like, "woah, that didn't take too long!!"

[IggDawg]

I tend to get motivated when I get something about my car set in my mind .

[boostjunkie]

I right there with ya!!

BTW, I read your reply in the "other" forum:D You said that you were running REALLY rich. I know that is the case with my car right now, even with the boost up where it is. I'm trying to figure out whether an adjustable fpr would help things out here.

I would've used my trusty s-afc that I got used a while ago, but alas, I wanted to have the thing installed as soon as a I could. So I was outside a few months ago in the 0 degree weather trying to install the thing based on an ecu wiring diagram for the turbo legacies that was COMPLETELY wrong!!

I ended up shorting out the display on the unit. It still modifies the MAF readings, however, I have no idea to what degree . . . So I've gotta find another used s-afc before I can do some WOT fuel correction.

That was my dumbarse mistake for this year!! Now I've got a $150 dash-ornament under my radio (I must admit it's a very clean install for only $10!!! Fit's underneath the radio where the pocket would normally reside).

[IggDawg]

Nice thing about our cars is that it won't learn around the settings like OBDII. also, it can force closed loop all the time to help with WOT. I don't mind running rich since it helps drive intake charge temps down. I'm not on the last bar of my AF gauge or anything. on a 10-LED gauge, I'm around the 8th or 9th bar at WOT. gets about 5-10% richer with the bleed valve on. at partial throttle tho, I'm almost on the rich side of stoichiometric instead of just plain "rich." I think if I was running closed loop at WOT I might get better numbers.

[boostjunkie]

Well you're still better off than me. I'm usually on 10 on my 10 bar led A/F gauge. Sometimes it'll drop into 9 . . . I'm sure it has something to do with my walbro. At any rate, I haven't noticed any driveability problems (and I like the fact that all that fuel's lowering my EGTs). I get about 20-22mpg, but if I punch it, or I drive in a lot of traffic, I'm seeing more like 17-18mpg.

If you want to just force open loop (I've never heard of the S-AFC forcing closed loop, but I'm still learing here too!), disconnect the ecu from the o2 sensor. Apparently, a couple people on this board have done this and show no signs of driveability problems. Your car will run open loop all the time. You can just leave the o2 sensor hooked up to the A/F gauge for monitoring purposes.

I'm sure there's more performance gains to be had by changing A/F ratios to be closer to stoich, but on the rich side of stoich, but for now, I'll make due with what I've got.

Another alternative might be to change the fpr to the adjustable type . . . I'm not sure if this is feasible or not, but be regulating the pressure to the injectors, at each injector pulse the cylinders would receive less fuel, thus leaning you out a little.

[91White-T]

I made a FCD with a check valve, works perfect, and it was less than $5
Even at 14psi, my A/F gauge was showing orange and green...

[boostjunkie]

Hmmm, you're dipping down into the yellow, huh? It must be my fuel pump!! Just be careful not to run too much more boost before changing the fuel pump . . .

[91White-T]

I'm just running 11 until I buy the better fuel pump... Even though there seemed to be no problems at 14psi with the stock pump, just wanna be on the safe side...

[boostjunkie]

Yup, you can never be too safe, which is why I'm skeptical about modifying the A/F ratios, until I get larger injectors that would necessitate the modification.

[Legacy777]

BTW, I read your reply in the "other" forum:D You said that you were running REALLY rich. I know that is the case with my car right now, even with the boost up where it is. I'm trying to figure out whether an adjustable fpr would help things out here.

Have you checked your fuel pressure at idle with and without the stock fpr connected?

That will tell you right away whether getting a larger/better fpr will cut down on running rich. You did read my post about fpr's correct?

Nice thing about our cars is that it won't learn around the settings like OBDII. also, it can force closed loop all the time to help with WOT.

Igg, where'd you hear that our cars won't learn around the settings? Also, you sure you got the closed loop part right......wouldn't it be open loop?

[IggDawg]

Things are normally closed loop. that's when it's reading from teh O2 sensor (unless that's open loop, in which case I've go teverythign backwards). when you hit WOT, it defaults to teh clsoed loop map which only reads the MAF and a few other readings. engine temp and whatnot. doesn't read the O2 sensor. the S-AFC can force closed loop mode all teh time. or so I've heard. presumably the advantage of this is that it woudl read the O2 sensor at WOT and lean things out a little. Not neccecarily into stoich even, but at least less rich . That's my understanding at least, and I was wrong once back in '82 so it could happen again.

I heard about the OBD1 thing from a buddy of mine with a Prelude. the Prelude guys like OBD1 better than OBD2 becuase, at least on their cars, the computer doesn't learn around things like the S-AFC and bolt-ons (I/H/E) nearly as much as OBD2. there is some learning but just not so much. This info comes from honda-tech, not club-si, so I take it to be true of the Preludes at least. I assumed this would be true of most OBD1 cars including ours. Again, reference the "82" comment above.

[IggDawg]

I made a FCD with a check valve, works perfect, and it was less than $5
Even at 14psi, my A/F gauge was showing orange and green...

Is there any problem with doing this? I tried it tonight, and got mixed feelings about it. I put a check valve inline with the MAP so it can see vacuum but not positive pressure. My AF gauge is still reading as rich as normal, and my boost is unaffected (as it should be since it's an MBC). outwardly I can neither see nor presume any change in fuel or air delivery by using this method. it's actually a pretty bright idea. my car didn't seem to pull as much as usual though. granted, my tranny never got abouve 105* or so since it was so goddamn cold out tonight. so it might be because I'm turning maple syrup through my TC instead of nice hot oil. can any of you think of any reason at all this wouldn't work? does the MAP do anything besides help out the FBC and provide readings for boost cut and fuel cut? my car drove essentially as it normally does. I'll give more info tomorrow morning when I can get some time behind the wheel with the tranny properly heated.

[vrg3]

Things are normally closed loop. that's when it's reading from teh O2 sensor (unless that's open loop, in which case I've go teverythign backwards).

No, right, that's closed loop. The feedback loop is closed, since the ECU selects an injector pulse width and receives feedback from the oxygen sensor.

when you hit WOT, it defaults to teh clsoed loop map which only reads the MAF and a few other readings. engine temp and whatnot. doesn't read the O2 sensor.

The open loop map.

the S-AFC can force closed loop mode all teh time. or so I've heard. presumably the advantage of this is that it woudl read the O2 sensor at WOT and lean things out a little. Not neccecarily into stoich even, but at least less rich :D .

I don't know how it would be possible to force closed loop except to tell the ECU that you're not getting boost (if it's a turbo) and that the throttle is not being pushed very far. Even then, the airflow signal alone should be enough to make the ECU go to open loop or at least throw CELs due to the readings from the pressure and throttle sensors.

I think you might be a little mistaken; it'd be very useful for the S-AFC to be able to force open loop, because then the ECU wouldn't try to work around its manipulations of the airflow readings.

Also, you can't really use a stock narrow-band oxygen sensor for any purpose other than tuning for stoichiometric ratios. "A little rich" could mean anything, since these sensors give an output voltage that pretty much just says "rich" or "lean." That's one reason the WRX uses a wide-band sensor.

I heard about the OBD1 thing from a buddy of mine with a Prelude. the Prelude guys like OBD1 better than OBD2 becuase, at least on their cars, the computer doesn't learn around things like the S-AFC and bolt-ons (I/H/E) nearly as much as OBD2.

I don't think this is as true for Subarus as for Hondas. There were huge differences between Subarus and other cars in the OBD1 days. For example, our cars run happily without an oxygen sensor all the time. My friend's G20 pretty much died without it.

The factory service manuals for our cars do describe a learning fuel management system.

[LegacyT]

I just learned the stck pump is good for maxing out the stock turbo. ~15-16 psi. You'd only need a better pump if you want a massive amount of power.

Mark,

[boostjunkie]

Have you checked your fuel pressure at idle with and without the stock fpr connected?

That will tell you right away whether getting a larger/better fpr will cut down on running rich. You did read my post about fpr's correct?

I read your post about fprs and I understand the idea of being able to regulate the fuel pressure to the injectors at idle, however, is that a good indication of whether the fpr will regulate the pressure to the proper amount under boost? I was thinking that if you run a lower fuel pressure at a certain vac/boost it would lean out the mixture. With an adjustable unit, I could see holding normal pressures at idle and tweaking them to be a little lower than the stock fpr regulates while under boost to lean things out a bit.

I heard about the OBD1 thing from a buddy of mine with a Prelude. the Prelude guys like OBD1 better than OBD2 becuase, at least on their cars, the computer doesn't learn around things like the S-AFC and bolt-ons (I/H/E) nearly as much as OBD2.

I think the idea with OBD2 ecus is to regulate emissions . . . that's all. The parameters in the ecu are much tighter allowing for less performance "space" to work with. OBD1 cars simply don't have these tight tolerances of sensor readings and such and more rely on mechanical measures to control fuel and airflow into the engine, whereas the OBD2 engines use more sensor based applications.

In order to produce more and more power, you're going to have to dip into less emissions friendly cars. OBD2 ecus will see this, and throw a code. OBD1 ecus don't.

FWIW, have you seen the engine diagnostic codes for OBD2 cars? The list is freakin ridiculous!! Taking a look at Josh's code list for our OBD1 ecus, I count something like 30-40 codes. The ecu only needs to know the essentials for keeping the car running smoothly, rather than concerning itself about emissions.

THANK GOODNESS!! I just received my notice for emissions testing last night . . . Um, not worried at all!!

[Legacy777]

Igg, I think you got some stuff mixed up. vrg3 did a good job of explaining things, I'm going to elaborate on it though.

For our cars the only difference between closed loop and open loop is that in open loop the ECU does not take the O2 lambda correction factor into account when adjust a/f ratios, and in closed loop it does.

Our cars run quite a bit in open loop. I've unplugged my O2 sensor and let the car run happy as a pig and get no check engine light or anything.

As vrg3 said.....subarus were quite different then other manufacturers in the day. My mom's 90 yota pickup would barely stay running when her O2 sensor was bad. My car, I probably can take the sucker out.


boostjunkie, what I said still does hold true, but what you're saying about having higher/correct pressures under boost is right too. It is a balancing act. Getting the pressure right at idle, but also making sure that you have a high enough pressure under boost to keep the injectors happy.

[Legacy777]

Also......like you mentioned.....OBD2 was introduced for one main reason, but had good implications towards a few others.

Emissions & emission testing was the biggest issue. Second was to get all the auto manufacturers on a standard for diagnostics so people other then dealer can run the diagnostics on it.

[IggDawg]

I made a FCD with a check valve, works perfect, and it was less than $5
Even at 14psi, my A/F gauge was showing orange and green...

Is there any problem with doing this? I tried it tonight, and got mixed feelings about it. I put a check valve inline with the MAP so it can see vacuum but not positive pressure. My AF gauge is still reading as rich as normal, and my boost is unaffected (as it should be since it's an MBC). outwardly I can neither see nor presume any change in fuel or air delivery by using this method. it's actually a pretty bright idea. my car didn't seem to pull as much as usual though. granted, my tranny never got abouve 105* or so since it was so goddamn cold out tonight. so it might be because I'm turning maple syrup through my TC instead of nice hot oil. can any of you think of any reason at all this wouldn't work? does the MAP do anything besides help out the FBC and provide readings for boost cut and fuel cut? my car drove essentially as it normally does. I'll give more info tomorrow morning when I can get some time behind the wheel with the tranny properly heated.

^
|----I just wanna bump this question since it got lost in all the OBD stuff .

Josh - yeah, I said "closed" when I meant to say" open in reference to WOT. you should see me with "left" and "right." I'm directionally dyslexic. I heard about the AFC forcing closed loop on NASIOC in the NA forum. a few RS guys were talking about it.

[boostjunkie]

Josh - yeah, I said "closed" when I meant to say" open in reference to WOT. you should see me with "left" and "right." I'm directionally dyslexic. I heard about the AFC forcing closed loop on NASIOC in the NA forum. a few RS guys were talking about it.

Hehe, your lefthand makes the "L" with its thumb and forefinger . . . For future reference

[91White-T]

I just learned the stck pump is good for maxing out the stock turbo. ~15-16 psi. You'd only need a better pump if you want a massive amount of power.

Mark,

Anyone actually try 16psi with the stock pump?

[boostjunkie]

I believe milehi has done some research with the stock pump and found it was the limiting factor in making big power . . . moreso the the injectors were . . . I don't know what the limits were.

[vrg3]

Is there any problem with doing this? I tried it tonight, and got mixed feelings about it. I put a check valve inline with the MAP so it can see vacuum but not positive pressure. My AF gauge is still reading as rich as normal, and my boost is unaffected (as it should be since it's an MBC). outwardly I can neither see nor presume any change in fuel or air delivery by using this method. it's actually a pretty bright idea. my car didn't seem to pull as much as usual though. granted, my tranny never got abouve 105* or so since it was so goddamn cold out tonight. so it might be because I'm turning maple syrup through my TC instead of nice hot oil. can any of you think of any reason at all this wouldn't work? does the MAP do anything besides help out the FBC and provide readings for boost cut and fuel cut? my car drove essentially as it normally does. I'll give more info tomorrow morning when I can get some time behind the wheel with the tranny properly heated.

A check valve should work just fine as a fuel cut defender. To be safest, you would probably want to plumb the line coming off the check valve back into the intake before the turbocharger (the same way a blowoff valve plumbs back into the low-pressure side of the intake).

The ECU does make use of the pressure sensor, though, for more than boost control and fuel cut. I think it retards timing and richens the air/fuel ratio as manifold pressure rises.

Don't forget that almost any manufacturer that sells a fuel cut defender will warn you not to use it unless you also have other engine control electronics to maintain a good fuel mixture and good timing when in high boost.

One disadvantage to a check valve or a simple voltage clamp is that you completely lose your overboost protection. Overboost protection makes a good deal of sense, so if you're using a simple kind of fuel cut defender, you might want to implement some other kind of protection in its place, like a popout valve or something.

It might be nice to make a defender that would maintained the existing fuel cut. For example, say fuel cut happens at 13psi and you want to run 16psi. If the circuit would output the actual pressure from -15psi to 13 psi, then output 13psi from 13psi to 16psi, and then output some reading higher than 13psi if the pressure was above 16psi, you'd have a decent setup. I wonder if this makes sense to anyone else. A simpler way to do it would be just to scale all the readings down, although that would mean that the ECU would never have the correct reading. It'd be easier to do, though; just a voltage follower and a voltage divider.