legacycentral bbs

I just upped the boost for the first time yesterday. The only mod I have is a Saab 900 intercooler. We figured 10psi would be a good place to put it. Well, it was at 10psi in 1st and was slightly higher in each succeeding gear. In 5th gear it was at 12psi. I was a bit weary of letting the turbo spool up to 12, but figured what the hey. Not even 2 seconds while at 12 pounds, the car acted like I ran out of gas. It was the same feeling I had last week when autocrossing, and took a long, wide right turn into a slalom. I'm not sure what detonation or fuel cut feels like or sounds like, so could someone help me out?

sounds like your ecu is displaying fuel cut off which will happen at around 12 psi. does it rather abruptly cut out and then come back but with less power. 12 psi should be fine for the stock turbo espeially with an intercooler and at least 91 octane fuel. it is just really annoying. get a reprogrammed chip, programeable ecu, afcr, or fcd. most liklely that is what it is. is that how you would describe it?

I Don't think its detonation. You wont really feel any difference in power when the motor is detonating, the only difference is a sound like small pebbles in a tin can. Boost/fuel cut is an ubrupt on/off in power feeling, like asthough the ignition is turned off. When you ease up on the throttle power will come back on. Very noticable. Factory boost cut is activated at 13 psi. I think your feeling fuel cut, as most guages aren't perfectly accurate, the 12psi or so you see on your guage may actually be 13 psi read by the ECU. You can always turn the boost down 1-2 psi or get a FCD if you want to go above fuel cut.

Mark,

also what are you using to control boost. I assume a mbc. but what kind?

for having hit the fuel-cut 5-6 times this weeks, that definitively sounds like you hit the fuel cut. It happens just over 12psi, and when the boost is at this level for 10-20 sec in a row.

sounds like fuel cut to me as well. In reference to your auto-x incident with the lack of power on a long sweeping turn. All subarus apparently get that when running a quarter tank or less of gas. Happened to every suby last year at one event, until we realized that the gas went to one side of the tank and wasn't getting picked up by the pump. Can't remember if it only happens when you turn one way or if it's in both directions. Anyways food for though.

good luck

I am using a mbc. I'm not sure what kind. It's actually just a loner until I can get one. It was an abrupt hesitation. As soon as it happened, I let off the gas and didn't let it get up there again. I turned it down just a bit. Now, it gets a little past 10 pounds in 5th gear. About the auto-x, I did have less than 1/4 tank. I figured I was getting starvation when it happened. I don't know, I may be a little too cautious, but I didn't race after it hesitated the second time at the track. Are there any negative effects of fuel cut or starvation?

the first situation was fuel cut, the auto-x situation was definately fuel starvation. it happened to me once with less than 1/4 when i tried to drift around a dry corner.

sounds exactly like fuel cut.

where's your gauge tapped? depending on the location of the tap for the boost gauge, you might be seeing something different than the MAP is seeing. and yeah, gauges aren't always right on. mine's about .05 MPa off . and that's genuine subaru parts (wrx boost gauge)

RE: Fuel starvation - It doesn't happen with every Scoob. It would happen to me in my old RS with less than 1/4 tank on sweeping right turns. In my WRX on race tires (which is setup enough for me to take 2nd out of 81, 1st out of 120-ish, and 2nd out of 140 at recent autox's), I've run down to about a gallon left in the tank and never had fuel starvation.

The boost controller is measuring from a vaccum hose coming directly out of the intake manifold. The gauge and the ecu numbers probly don't match up.

You can bypass the fuel-cut "phenomena", by making a small (1mm) hole to the pressure regulator vacuum hose. The small ticking "canister" inside the right fender (- about the size of a 35mm film canister.)

This is done easiest by installing a plastic connector to the middle of the hose and then burning (melting) a small hole with a heated needle to it.

This 1mm hole will lessen the actual pressure in the regulator by appr. 0,2bar (psi???), and thus preventing accidental fuel-cut dependent of air temperature and humidity - and also preventing fuel-cut in case your turbo has a high peak boost before settling to normal.

Bu sure to have a accurate boost gauge, so that you know what boost youre running. The EJ20 (or EJ22) can take safely 1,3 bar boost with a 98 octane (the highher pump octane in Finland, the lower is 95). With american 92 oct you could expect reasonable safe level of 1.0 bar without knocking.

Teesaa, just to clarify, I think you mean the pressure exchange solenoid, not the pressure regulator solenoid.

The pressure exchange solenoid is right above the boost control solenoid; both are cylindricalish in shape. The pressure exchange solenoid is brown plastic, and has three vacuum lines coming off it. One is short and goes straight to the pressure sensor (little square black plastic thing), one has a little cylindrical air filter installed directly on it, and one goes to the manifold. That last line is the one to put the bleed into.

You're right. My mistake about the "gadget". All - pls take this vrg3:s reply as a clarifying supplement to my post.

Ok so you install this little contraption on the vacuum line that goes from the intake manifold to the right hand side of the pressure exchange solenoid (brown thingy)? My boost guage is tapped into this line, will doing this give inaccurate readings?

Mark,

By "right hand side" you mean the side pointing towards the engine, right? If so, that's correct.

You may get inaccurate readings on your boost gauge; to minimize it I'd suggest putting the bleeder as close as possible to the solenoid, and putting the tee to your boost gauge as close as possible to the manifold. With it set up that way you should be fine.

Usually you want your gauge as close as possible to the manifold anyway, to see what the engine's actually ingesting.

You're right - If it is on the same line, the readings will be inaccurate, as some of the pressure will be relieved from the little hole.

Why not install the gauge to the line coming from the turbo "nipple" ?

Where is the nipple on the turbo? Is there another place on the intake manifold where I could tap the guage into?

Mark

It is on the engine side of the turbo's compressor housing - the place the pressure hose leaves the housing. Slightly under the intake resonator box.

The vacuum line coming off the nipple on the wastegate?

Mark,

Where you should tap pressure for your boost gauge depends on what you want to measure. Tapping the compressor outlet will tell you what pressure the turbocharger itself is producing. Tapping just before the throttle will tell you the pressure that the engine would see if there were no throttle (basically the turbo outlet minus intake/intercooler pressure drop). Tapping from the intake manifold (the most common one) tells you what pressure or vacuum your engine is seeing. It's good to be able to keep an eye on your engine's manifold vacuum and pressure, so that's where I put it.

Compressor outlet pressure isn't always as meaningful when the throttle isn't fully opened. Or at least not as meaningful to me, since I'm not smart enough to make use of it. :)

Are there any other manifold nipples I could tap into other than the one that goes to the map sensor and boost soleniod?

Thanks,
Mark

There is one on the rear driver side of the manifold that goes to the blowoff valve; look for the blowoff valve under the big plastic pipe just upstream of the throttle, and follow the small hose coming off it.

There's also the attachment for the brake booster... Much larger, though.

be careful when bleeding off air to the map sensor, if you bleed off too much it will run super rich upon startup (especially when cold) and will lean out under manifold pressure (boost) i suggest using an adjustable bleed valve to do this and go up in small increments or get it dynoed and done proffesionally. I have the australian RS Liberty with water air intercooler. factory boost cut on mine is set to 14.7psi with the adjustable bleed valve on the map sensor i have it set to 17psi boost cut. I fully have to warm my car up on startup because if I take off and drive it like I stole it when I first jump in it will actually begin to foul plugs because it runs richer down low and it will run a bit leaner at boost.

The Legacy Turbo -- the North American BC/BF turbo at least -- doesn't really fuel based on the pressure sensor. You certainly won't get overly rich mixtures at startup or overly lean mixtures at boost.

At boost, you will get mixtures that are less rich than they were specified to be by the ECU engineers, though.

You should be aware that a bleeder is basically the same as the fuel cut defenders that change the slope of the voltage vs. pressure curve rather than clamping the voltage. When your manifold pressure is 10psi, for example, the ECU may think it's only 9psi. So, it would retard timing and enrich the mixture less than it probably should.

Note that this is does not mean the ECU will inject the appropriate amount of fuel for 9psi. Fueling is primarily based on the MAF sensor, so the mixture will still be much richer than the stoichiometric. It just won't be as much richer.