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06 LGT won't boost past 14psi


kred

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So on this 06 spec b, it's got a VF52, Perrin catted downpipe, and stock everything else (for now). Tuner is trying to hit 16-17psi on stage 2 map, but it never sees above 14 even making significant changes to wastegate duty tables. Runs flawlessly, no pre-turbo exhaust leak, no boost leaks detected, tried changing boost controller with no effect, wastegate actuator moves freely.

 

Any ideas why it would be limited? Could the factory catted uppipe be choking it from building more boost? Any input is appreciated.

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I don't think so. I had a catted up pipe with a vf40. On stage 1, I was able to reach 16.9 psi.

On the other hand, now I am stage 2 (catless up and hi-flo dp). Target boost is now 17-18 psi and only goes as high as 15.5 :confused:. My long term fuel trims look great too. Also trying to figure out why...

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Make sure your wastegate "flapper" is closing properly. I've seen instances when the bushing in the turbo housing comes loose and allows the wastegate to be off-set and not seal properly.

 

Seems to seal perfectly fine, doubt there's any wastegate leak. It builds boost consistently to 14psi by like 3700rpms in 3rd and holds that number no problem. And as boost tappers to redline, it matches those lower boost targets in higher rpms. I wonder if it could have the wrong restrictor pill from the stock vf40 setup?

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Ok, so I test drove the car as it is last night, peak boost was 14.3psi. Then I disconnected the wastegate actuator hose to see if the car is capable of building more boost. With someone else test driving as I datalogged, the car quickly saw 17+ psi in a 2nd gear pull. So what does that narrow it down to?
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Interesting. That makes me want to try this now. What did your tuner say about the outcomreof this test?

 

Said he's going to compare my map to other maps, maybe suggesting something in the tune?

 

If you do try, be extra cautious to watch a boost gauge or have someone else drive while you datalog. I'm sure you could blow your tmic off or risk other damage if you overboost too far.

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  • 5 weeks later...
Same problem here after upgrade to VF52, but I'm only hitting 9 psi. Cobb thinks it's an air leak somewhere.

 

My issue was actually the tune itself. But with only 9 psi, I'd say run a boost leak test first. Or with the car idling, spray some MAF sensor cleaner on common leak areas (intercooler inlet and outlet, intake manifold, turbo inlet, etc). If you get the idle to stutter a bit, you've found a leak.

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Sprayed soap/water on all the hose clamps/fittings, no bubbles. Also tried carb cleaner with no luck on idle change.

 

Cobb says to try unplugging wastegate hose to see if its a wastegate issue. My mechanic that put in new VF52 thinks the wastegate is out of adjustment or wants to try MBC to rule out EBC...

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Yeah, just as a cheap and quick troubleshooting tool. Hopefully it'll show me which way to go or what is bad.

 

SOLVED. Mechanic thought it was a leaking wastegate housing. Upon further inspection, the restrictor pill (1.2mm) was missing. Replaced with a 1mm pill and now I can boost to 18+ psi.

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