Negative Boost?

[SrsBsns]

I switched maps from slot 1 (Stratified 91 Tune) to slot 2 (Stratified E30) tune after filling up with E30.

On the way home, the car ran fine, but my AP3 was reading strange boost #'s. At idle, I was -10 psi. At light load, I was at -5psi. With a little bit of gas, the highest I hit was just under 12lbs, but I didn't get on it hard at all to test. For the majority of the drive, I was between -10 and -5lbs of boost, even under load, which is know isn't right.

Normally, boost is only slightly negative at idle and I start building boost almost immediately while on throttle. My peak boost levels on my normal commute are never higher than 24lbs but with normal driving, I see peaks of about 17-18lbs.

The car drives fine. It feels like it has power, but I didn't go more than 50% throttle or 4-5K RPM's. I get a loud PSSSHHH every time I let off the gas because of the Boomba BOV spacer. So I'm assuming I'm still building boost and that things are fine, but somehow the AP3 isn't reading correctly.

I've searched but haven't found much. Most threads are about neg ign timing or about slight negative boost levels at idle due to vacuum.

I'm going to switch maps, but do you know what might cause this? I want to make sure I'm not doing any harm to the car. I did log it when I got closer to home and can post that if it helps. I'm not really sure how to read the datalog.

 

[felopr]

-10psi at idle while warm seems normal... Is call vaccum. You are never 100% "on" boost. If your car was naturally aspirated, you never see boost (as retarded as that sounds i know). Car engines are, figuratively speaking, is a vaccum pump

 

[slopoke]

You are reading normal vacuum pressure. During cruise my stand alone boost gauge always read negative. Going up a slight incline at cruise the gauge would read 0.

 

[SrsBsns]

So maybe the -10 is normal, but under throttle, I'm boosting -5lbs and I know that's not right.

How can I hear the "bov" if I'm not making boost?

 

[Clint Beastwood]

So maybe the -10 is normal, but under throttle, I'm boosting -5lbs and I know that's not right.

How can I hear the "bov" if I'm not making boost?

Well, how much throttle - like if you go WOT and the turbo spools, does it go to positive pressure? It's normal for you to get vacuum until your turbo spools. My grand national showed vacuum until almost 3200rpm, then the boost gauge flipped waaaaaaay in the other direction

 

[SrsBsns]

Well, how much throttle - like if you go WOT and the turbo spools, does it go to positive pressure? It's normal for you to get vacuum until your turbo spools. My grand national showed vacuum until almost 3200rpm, then the boost gauge flipped waaaaaaay in the other direction

Yeah, so I can hit boost... I did one WOT pull this morning and hit 24lbs. But it didn't seem to hold. Started falling to about 12lbs.

The reason I'm convinced something is off is because I've had the AP set up and have been watching it regularly while driving for the last... 6 months at least. Since the fill up last night and switching map slots, it's different.

When I'm at partial throttle, driving normally, I'm used to seeing between 2-8lbs of boost. Now, under the same amount of throttle, I'm seeing -2lbs. When accelerating, I should not be seeing negative boost numbers but I am.

Tonight I'm going to try to lift the car up and take a look. From the top, everything looks fine.

 

[FJ16]

You can accelerate and still not be hitting boost - it all depends on how much throttle you're using and what your tune is setup to do. If you're going from one Strat tune to another, I wouldn't think there would be much difference in the throttle feel... but I haven't driven an E30 vehicle to compare with.

 

[SrsBsns]

You can accelerate and still not be hitting boost - it all depends on how much throttle you're using and what your tune is setup to do. If you're going from one Strat tune to another, I wouldn't think there would be much difference in the throttle feel... but I haven't driven an E30 vehicle to compare with.

Agree, but my driving style is consistent. At the same throttle, I should be hitting the same boost I normally do. The problem now is that under the same throttle, it not only tells me that I'm not making that amount of boost but I'm still in vacuum.

 

[Clint Beastwood]

Your stock DV might be leaking, that would make your boomba bov spacer sound farty.
For what it's worth, the Turbosmart EM DV vr2 is pretty spectacular. It's really fast like the GFB, but you don't have to disassemble your stock DV to install it. I bought both the noisy one and the quiet one and wound up keeping the quiet one. I didn't like the constant whooshy fart of the dual port DV, the sound of the plumb back vr2 + an intake sounds roughly the same but it's not blowing off when backing out of parking spaces and stuff the stock DV is not a high-quality part.

 

[purityracer316]

Your stock DV might be leaking, that would make your boomba bov spacer sound farty.
For what it's worth, the Turbosmart EM DV vr2 is pretty spectacular. It's really fast like the GFB, but you don't have to disassemble your stock DV to install it. I bought both the noisy one and the quiet one and wound up keeping the quiet one. I didn't like the constant whooshy fart of the dual port DV, the sound of the plumb back vr2 + an intake sounds roughly the same but it's not blowing off when backing out of parking spaces and stuff [emoji14] the stock DV is not a high-quality part.

I have the Turbosmart EM BOV VR2 Plumb Back along with the Ramair Cone Filter Kit and I can definitely hear the psssshhhh and the light sneeze sound. I like it a lot compared to that annoying spacer I had.

But back to the OP it's normal. Stratified also with 91, 93, and E30. Just normal driving in the morning warming up my car I rarely go past 0 psi on my way to work shifting every 2.5K

Sent from my SM-G973U using Tapatalk

 

[SrsBsns]

So hooked up the AP3 to my computer and updated my firmware. It seems to be reading normally now.

The issue was that under acceleration, it was still showing negative boost which is absolutely not normal, especially with the Stratified aggressive tune. When I breathe on the throttle, I start building boost.

 

[Clint Beastwood]

So hooked up the AP3 to my computer and updated my firmware. It seems to be reading normally now.

The issue was that under acceleration, it was still showing negative boost which is absolutely not normal, especially with the Stratified aggressive tune. When I breathe on the throttle, I start building boost.

Oh sweet that it's solved. My only other thought was maybe bearings going bad in the turbo so it was an obstruction instead of a compressor, then it'd spin up and make boost. Firmware issue is much better than that

 

[SrsBsns]

I thought it was so strange that it happened right after I switched map slots. Nothing else was noteworthy during that time, so I was really hoping it was something simple like that.

 

[DoomsdayMelody]

Agree, but my driving style is consistent. At the same throttle, I should be hitting the same boost I normally do. The problem now is that under the same throttle, it not only tells me that I'm not making that amount of boost but I'm still in vacuum.

No, horsepower is load driven.

When you press the skinny pedal, you are commanding the ECU to deliver an rpm. The ECU will look at engine speed and air data and make the necessary fueling and air adjustments in order for you to reach that rpm. This is why it’s impossible to see full boost in neutral, there isn’t enough load for the engine to need that much boost. The engine hits the target rpm without needing the additional fuel/air. So under light throttle application, you may or may not see boost, it depends on engine load and how rough you are with the pedal.