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Crazy boost variations on multiple pulls

3K views 14 replies 5 participants last post by  Southerncross 
#1 ·
2014 Nismo RS 6mt, EFI Logic IC pipes, Turbosmart Kompact DV, otherwise stock

Well, since I've been having weird issues with my car since my factory DV gave up, I got my boost gauge installed to troubleshoot. Made some 3rd and 4th gear pulls from 2500-6000 tonight. Holy crap this car has issues. I was seeing as high as 24psi and as low as 11psi under WOT. None of the runs were consistent with each other which is what is aggravating me. I'm starting to think this car is totally mod averse because it did something similar when I was running just a B pipe with no exhaust; coming into boost really hard then dialing it way back to the point the car felt like it was falling on its face. It seems like it has no problem holding pressure in the Intercooler pipes, but just can't stabilize the boost at all. Give me some ideas folks. This **** is making me wanna buy a Subaru.
 
#2 ·
The boost gauge is tapped where others have tapped theirs; at the reference port line for the DV, down by the radiator to the right of the hardline.

Ok, well that makes some sense. The biggest problem is it's erratic in how it happens. It didn't do this stock, only since I started trying to mod the car. This morning it ran fine on the interstate ramps doing 3500-6000rpm pulls through 3rd. It would hit boost around 3500 and spike to anywhere between 18-21psi then wave around like mad for a couple hundred rpm and would settle at about 16psi until 4500rpms, then taper back to 11-12 by 6000. It's never consistent though and sometimes it will hit extremely hard, spiking to over 20 then dialing back to about 8-9psi, then finally plane out around 11-12, not even reaching or holding 16psi. I'm starting to think the design of this system is crap if it can't handle stock boost levels with small increases in air flow. Would an aftermarket boost controller fix this? If I'm gonna have to redo everything Nissan provided to control boost then I'm gonna build a manifold and upgrade the turbo because this is retarded.
 
#3 ·
Either your boost gauge isn't installed right or you have boost leak somewhere, you shouldn't be boosting over 16psi if you don't have a MBC
 
#5 ·
Without even looking at the gauge, does it FEEL like its ranging between 8 and 20 psi? You should be able to easily tell the difference. If it doesn't feel any different, then I'd say there's something wrong with the gauge itself, or the install of the gauge.
Is it electric or mechanical boost gauge?
 
#7 ·
what boost gauge do you have? and can you take a pic of where you have it tapped?
 
#8 ·
I'll try and get a pic today. Thanks for the replies guys. I did a few more runs last night and it seems the colder it is outside the higher it spikes and the more erratic it is. 99% sure I don't have boost leak considering one of my runs held 18psi the whole run in three gears.
 
#9 ·
Check the vacuum line to your wastegate for pinching, also, follow the lines from the factory boost solenoid, check those for pinching. Major boost spikes like that are usually a sign of wastegate related issues. Also, another test you can do, move the boost gauge reference from the recirc line to one of the lines feeding the boost solenoid and see what your boost looks like there.
 
#11 ·
Makes sense wakky, I ordered a new boost gauge this morning and will double check again all of the current connections, but I didn't see any obvious issues. I'll see how it does with the new gauge installed and report back. Thanks for the help guys.
 
#12 ·
Having the torque pro app is helpful when setting up your boost gauge also because the torque pro app will tell you what your ECU is reading for boost as from what I can tell it reads what the turbo is boosting and that should be pretty close to watch your boost gauge is reading if you have no boost leaks or anything.
 
#15 ·
I posted on the Facebook page last night that I figured it out when I was installing my new boost gauge: the factory rubber hose from the charge pipe (turbo) to the pressure solenoid wasn't anything more than vacuum line and not pressure rated, and was literally blowing up like a balloon. After I swapped it to fuel injection rated hose my problem went away and boost stabilized. Car runs great now.
 
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