Hey Guys,
I have the LNF engine in my kit car, its running and driving fine. I am questioning if the engine is making full power though as my butt dyno is not impressed on the track.
Some history:
-I have the upgraded MAP sensors
-Trifecta email tune (I have no idea what kind of tune it is, I assume a 24 psi)
-MAP/MAF sensors are all placed in the same locations as you would find on a OEM motor
-BPV solenoid is "bypassed" (I leave it unplugged due to compressor flutter everytime I lift off the throttle when its plugged in)
-I have a pressure gauge teed into the BPV hoses so it is reading the air pressure in the cold side of the intercooler plumbing.

At full throttle in 3 and 4th gear my gauge (you can see in the video) is making about 12-14 psi. (0 psi is when the needle is at the 12oclock position and 10psi is at the 6oclock position.

I was also logging both MAP sensors with the OBDII torque app on my phone and it is telling me that the sensor in the intake manifold is making 12 psi boost (red line on graph), but the sensor in the intercooler plumping (where my pressure gauge is teed in) is making 24 psi (blue line on graph).

So why would there be such an offset in pressures between the two sensors. (btw the sensor (blue line) is reading 3-4psi boost when the throttle is let off, or at idle) I assume that is not normal.

Skip to about 22:40 in the video to see the gauge I am referring to:

Let me know if anything here seems way off or if there is a simple test/check I can perform as a sanity check. The car weighs about 1400 lbs (1800 with occupants & fuel) I am assuming that it wound be making about 280hp at the wheels, but it just doesnt feel like it pulls that hard, maybe its just me. I may take it to a dyno to get actual HP numbers but i thought I would ask here first if there is anything obvious.

 

K why would it flutter when u leave the bpv plugged in but not when u unplug it, that doesn't make sense. 24 psi trifecta tune u should be at around 300-315 whp. I'd advise u to get the Zfr turbo and hp tuners and get a good tuner from here to tune u, u won't be disipointed anymore after that.

 

Well maybe the flutter is related to this issue? If you want to see an example of the flutter issue, see my previous topic: https://www.cobaltss.net/forums/prob...engine-308952/

Its been awhile since the initial notice of the fluttering issue and leaving it unplugged, so a few weeks ago I plugged it back in just for fun to see if it was still doing it...yup. It sounds like a turkey gobbling everytime I let off the throttle, its soo annoying. I should take a better video of the flutter while driving sometime...but anyway, not to get too far off subject.

What are your thoughts on what my pressure readings are, why would one sensor read 10psi lower than the other? I assume, under boost conditions when the throttle is open, they should read about the same.

 

Bypass it?

 

ok u gotta explain what u unplugged. did u bypass the bpv solenoid? cause if u unplug it with bpv still hooked up to the solenoid it wouldn't open and u would get the same flutter. did u ever try changing out the solenoid? or bypassing the vacuum tank? we need a picture of what u have going on with the bpv solenoid, its very easy to figure out what the issue is with it, cause there isn't much to that system. ur boost sounds like u got a stock tune on that motor not a trifecta. idk what the readings should be on the sensors. I could check tomorrow.

 

You can watch the video that is in the previous topic about flutter to see that I am leaving the BPV solenoid unplugged. When I plug it in, the coil stays energized and the solenoid does not allow vacuum to the BPV, thus the BPV does not open when I let off the throttle. If I leave the solenoid unplugged, the "shuttle" returns on spring force and basically the BPV is directly connected to the vacuum supply of the intake manifold. Right now the vacuum tank is removed and the hose routing is exactly like the Solstice factory routing. (it didnt make a difference either way). The solenoid is brand new, and I can hear it shuttling back and forth when I manually apply 12V to it, so I am thinking that the solenoid is fine. Its just that the ECU us energizing it all the time. I also double checked that the two wires are connected to the correct ECU pins and that checked out fine.

One of my thoughts was that if one or both of the MAP sensors are reading something weird, that is what is causing the BPV solenoid to not be functioning properly. I did check those ecu connections as well, all good, and the MAP sensors are brand new. At that point, I just left it alone and went on my merry way. Now that I see such a difference in the MAP sensors, I am questioning what is going on.

 

Sounds like a vac leak- might want to check brake booster line fitting, o-ring on upper MAP, lines etc. Not sure if it matters in your case but some of the Trifecta tunes were "switchable" on/off from GM tune via cruise control switch iirc.

 

Ok it doesn't show what the lines are hooked up to, but the way it should be with vac tank bypass is , the right port should go to vacuum only. I did this with a check valve. The left side should goto boost only, on cobalt it's connected to lower charge pipe, and ur clear line should goto bpv. Is that how it's hooked up now?

 

Ok it doesn't show what the lines are hooked up to, but the way it should be with vac tank bypass is , the right port should go to vacuum only. I did this with a check valve. The left side should goto boost only, on cobalt it's connected to lower charge pipe, and ur clear line should goto bpv. Is that how it's hooked up now? YUP That is correct. And then my pressure gauge is teed into the hose that connects to the cold side IC tube.

Sounds like a vac leak- might want to check brake booster line fitting, o-ring on upper MAP, lines etc. Not sure if it matters in your case but some of the Trifecta tunes were "switchable" on/off from GM tune via cruise control switch iirc. Well I never did a vac leak, I should check that anyway. Brake booster port has a threaded plug with a big o-ring on it. The upper map sensor I actually fabricated a bracket to properly fit it since the upgraded MAP sensors dont fit, well you can make it fit, but it was asking for trouble (putting lots of stress on the sensor and poor o-ring sealing). I have no cruise control button, so hopefully that would not be the case...Vince should have figured that. I can check for leaks next weekend

Anyone willing to log their MAP sensors to see what the differences are between them?

Right now I am assuming that I am collecting the raw data of each sensor and that the phone app isnt converting the units or something like that. It makes sense that the one sensor is seeing vacuum, as that would be the one in the intake manifold. But it is strange that if I am teed into the cold side for my analog pressure gauge, I should be seeing 24psi as indicated by that sensor, not 12 psi. I remember in my last TC car I had to convert the MAP pressure from psi atmosphere to psi gauge or something like that...

 

Stupid question, but I just need to be certain. Are both map sensors the same? As in, does one have 2 hold down tabs, and the other only have one?

 

Man then idk lol only thing I can think of is even if bpv solenoid is new it could be defective or some weird craps going on with something somewhere. Maybe it's wired backwards lol.

Stock map sensors are 2 different ones, 3 bar are the same.

 

Both sensors are the upgraded ones with the single bolt hole mount, valid question. I should double check that the one on the intake manifold is secured. 25psi on a 1/2" hole =5lbs of force trying to push it out. The leak/pressure test should hopefully catch this.

 

I dont think a DC solenoid can be wired backwards. It just gets 12v and the ecu controls the grounding. If the wires were switched the coil would still be on/off in the same fashion, the coil shouldn't care what the polarity is...I pondered the same thing and came to that conclusion, but regardless I did check to make sure it was the way it was suppose to be. Over the next weekend I'll check for leaks, but in the meantime can anyone answer the question about the differences I have in the MAP sensor readings? Normal or no?

 

I always put silicone around the oring, if I don't it leaks on the charge pipe sensor but I don't do it on manifold sensor.

 

connect your bpv and remeasure. see what numbers you get. its supposed to gobble, or kicked puppy sound. the bpv is there for recirc of metered air. you are taking that air into your own loop. that turbos twin scroll wants the vacuum. put some ear plugs in and feel the pull.

 

no, the stock turbo doesn't gobble. it does a little with vac tank bypassed, but not really. the zfr gobbles. not a air hitting compressor gobble though, its different.

 

You seriously think I dont know this, or are you just being a dick? lol.. My question was to make sure he didn't accidently replace only one sensor, not to ask what the sensors consist of.

 

wol-shiver- The last time I drove it around with the solenoid plugged in, I didn't notice any power difference, just more obnoxious noise every-time I let off the throttle.
plugged in= gobble,gobble,gobble
unplugged= pssshhhh

 

Well well excuse me for not being able to read ur mind. I didn't even look who asked I just answered the question. Lol

 

Something is definitely messed up with that solenoid. Almost sounds like it's working in reverse. Plug it in with car running and see if the solenoid is open at idle. Sounds like its open then closes when u get off the gas. Lol weird. I just say screw it and just bypass it altogether.

 

It sounds like its hooked up incorrectly. Try a different routing (change the lines going to the turbo not the wastegate)

 

Could it possibly be an ECP tune? Or vice versa and it needs an ECP?

 

It sounds like its hooked up incorrectly. Try a different routing (change the lines going to the turbo not the wastegate) Changing the two hoses around (vacuum supply and pressure supply) will effectively be the same as leaving the solenoid unplugged.

Remember, when the solenoid is plugged in, it is staying energized. (the ecu is grounding the circuit) From what I can tell it stays energized all the time, and that is where the problem seems to be. I dont know why it would be stuck like that. I did check to make sure I had the ECU pin in the correct terminal and last I checked it was.

Could it possibly be an ECP tune? Or vice versa and it needs an ECP? Sorry I am not familiar with ECP, what is that?

 

Have u tried at all to swap out a different solenoid? I know u say it's working , but for ***** and giggles have u tried a different one?

 

I'll be checking over things again this weekend but I am starting to suspect that one of the two map sensors is reading incorrectly (reading higher than what the actual pressure is).
The sensor in question is reading 4-5 psi at idle or when the throttle is closed (located in the intercooler piping I think it should be just about zero pressure at idle), but goes up to 25 PSI under full load. I am wondering if the computer is using that to regulate boost and thinks I am making a lot more than what I am. That would explain possibly why the other sensor is reading about 12psi and that seems to match my mechanical gauge.
If that is the case, that may have something to do with the reason the PBV solenoid is acting strange.
Even better if that was the case, the engine has a lot more power than I have seen so far (which is kind of what I was expecting). I would guess that 12 psi would feel quite a bit different than 24 psi, this should be fun!
Is it common to see a MAP sensor fail like this? hopefully a swap of the sensors may reveal something.