legacycentral bbs

Since the FCD is the only part not yet working on my Electronic Controler, i decided to do a little trick to fool the MAP, until i solve the problem of my Electronic FCD.

It simply consist of a "T" and a Check-Valve, dispo. at any pneumatic equipment shop.

total cost, tax included : 16$.

I've tested it and it works pretty well !

Pics :
http://public.fotki.com/morgie/morgie/l ... cheap_fcd/


I love those Cheap mods

looks good to me.... can you give me any more info on that "check-valve", does it just release pressure after a certain psi? if so are they adjustable or do they come in set increments?

thanks, and nice work!

It's a simple check valve, it lt air pass in one way but not in the other.

There is no adjustements on it so anyting higher than 0psi and can open the valve, will be dumped into air.

you could add a little Adjustable valve in front of it to adjust the flow of air dumped into air.


While trying to find a proper restrictor for my Boost controler, i had to run with 16-17 psi (not for a long time), and Fuel-cut never occured.

One question about this check valve. I'm assuming you lose boost through this device, correct?

Wait, if anything above 0 psi is vented then doesnt that mean the sesnor is reading zero? What would be the difference in just disconnecting it?

The check valve lets it see vacuum but not boost, so it functions normally under vacuum.

I hazard to guess that the MAP sensor still sees boost, but not the same pressure as is present in the actual engine. Sort of like a manual boost controller changes wastegate pressure release.

I just installed that on my saab 900 IC setupe....works fine!!! 14 psi and fuel cut!!!

14psi and _NO_ fuelcut you probably mean ?

oops!! yeah I meant NO fuel cut!!!!

I thought he was oddly happy about hitting fuel cut

Great mod guys. You should post a LINK to this thread in the Forced induction forums at Nasioc.

One thing to watch out for -- the ECU has absolutely no idea about how much boost the turbo is producing if you do this. It probably won't retard timing and richen fuel mixtures quite enough. Be careful.

humm, that might explain why i run soooooooooo damn rich !

Morgie, is that sarcasm?

How do you know how rich your engine runs under boost?

I don't know what happend last night, but it was SOOOOOOOOOO fast...I don't know if the ECU learned to deal with the intercooler but it was realy quick...nothing to do with the last two days...It was raining...was it the water on the intercooler? Or the timing thing you're talking about...no timing retard so it's fast as hell...but it was still rich...even richer then the past two days...weird...

Vrg3 : it's not sarcasm... it much a conbination of factors.

I did this FCD mod almost in the same time i did the 'grounding mod' ... and since then, my AFR are always max green (the 2-3 last green lights on my gauge). I know all the theory about O2 sensors and temp and stuff, but i never saw my engine that rich.

Is it the FCD or the Grounding mod ? I dont know... but i dont beleive it could be the FCD.

Your gauge is reading higher than before. There are two ways that could happen - one is actually richer mixtures. The other is a richer signal from the oxygen sensor due to better grounding. You probably have both going on.

The 2-3 last green lights on a gauge hooked up to a standard narrow-band oxygen sensors don't mean too much... There's no question you're running quite rich, but high boost requires running really rich to be safe. A standard "air/fuel ratio gauge" can't differentiate between those two.

I nominate you for an EGT gauge. Ive been doing alot of homework recently (a boost level map with efficiency for the stock turbo will be posted soon) and many times I have read that an A/F gauge is always a secondary check against EGT.

The EGT was used to monitor health (or proper tune). When EGT wasnt in the correct range you would then look to A/F only to know wether it was too much air or too much fuel. Once you knew which side of the ratio needed to be increased you focused on the EGT until the numbers came back to spec.

Ciper : Ya that's why i want an EGT, and in fact i was supposed to get it on thursday but blablabla will only have it on monday... I'm eager to see the reading vs. my new A/F readings.

Cool. Clamp on or weld?

u pepole got the right idea but its all little messed up. first off where u put ur valve to cut the fule cut is wrong. not only can u blow shit up from that little brown sensor. u pepole mean well but its the sensore under the brown one, that is ur fule cut. the little black one with the one vacum line comeing out and going in to the brown one. put a one way vavle so it can suck the air from the fule cut sensore and not let pressure exit when u get past boost levles so it holds the preassure in one sucking motion sabbs r diffrent cars. 1991 subaru legacy turbo 2.2l motor is the only car in the world subaru has made very diffrent but very eazy. and to think there is so many things the same on that shit box sti it s all old legacy turbo tricks i love my 1991 turbo legacy. not only can i RIP any car on the road the cops think its plane old maryijane. ciao

nico,

Watch the profanity!

I think I have an idea for a better mod. Tell me how this sounds

On the line running from the intake (not between the switch and the sensor, but between the intake and the swithch) Install a pressure regulator like that used on an air compresser. If you havn't seen one its a peice of hardware with an outlet and an inlet. If you set it for 10 PSI the inlet pressure could be 50psi or 100psi yet the outlet will always be 10 or less.

Nico: Uh, no, Morgie has it right. The brown cylinder is a solenoid that allows the sensor to read either atmospheric pressure or manifold pressure. He put a check valve in the line that reads manifold pressure. If you put the check valve between the solenoid and the sensor (the little black thing you're talking about), then you could end up with incorrect atmospheric pressure readings depending on when the ECU checks it.

Ciper: I don't know for sure if that would work. It may depend on the way the regulator functions. Many of them only work right if they're actually flowing air. One that works kind of on the same principle as a return-line fuel pressure regulator might work, since it is essentially a relief valve with the outlet used as a return line.

If all you want is to clamp the reading at 10psi, that's easily done with only a few (like 3 or 4) dollars' worth of electronics...

Morgie's setup works fine. I set the boost at 15 psi just to try. Oh man...It pulls realy realy hard!!! And no fuel cut at all...