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Discussion Starter #1
Hey all, need some help. Have a 91 GTR that i picked up a little bit ago. It sat for about a year, so looked and ran a bit sluggish, but I saw the diamond in the rough. I've fixed a few of the nagging issues with brakes and electrical wiring (previous owner tried wiring a turbo timer and an APEXI AVC-R and said he just didnt complete it, however i take that as he didnt know what he was doing) so now i'm onto the next issue: turbo sputter.

it came with a turbo sputter that I attributed to a leaky vacuum line (a few sections were clearly dry-rotted). The sputter sounds like its only one of the turbos, so I replaced all the vacuum lines on the turbo side and the ones around the boost sensor that hook in below the plenum. Still sputters under boost until you get to about .6bar. I left the boost restrictor in place, so it should cap at .7bar from my understanding but once i get through the sputter the boost will climb to .9bar smoothly.

I checked the spark plugs, they're all good. Now I'm new to this platform and don't have a lot of experience as a mechanic, but is there any possibility its a fuel issue? Maybe there's a leak somewhere on the plenum gasket or on the exhaust before the turbos? Any other ideas before I start taking off plenum/turbos?

Other symptom of the sputter is that it smokes when i try to accelerate under boost. Smells like its running a bit rich even at idle. Any help would be greatly apprecaited.
 

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If your still running the MAF's.
The solder is proned to drying up and cracking.
If you have a friend with a gtr it's a simple job to just take off and try out.
 

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Discussion Starter #3 (Edited)
If your still running the MAF's.
The solder is proned to drying up and cracking.
If you have a friend with a gtr it's a simple job to just take off and try out.
great, I'll take look tonight. And is it the solder on the MAF connector or in the MAFS itself?
 

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Discussion Starter #4
pulled the tops off both MAFs and it seems as though a previous owner had already re-soldered then pins. Everything looks solid and doesnt show any sign of cracking.

Anything else I can check?
 

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Discussion Starter #6
It's called surge, quite common in the GTO world.

Is it worse at part throttle?.
No, about the same across the board from 1psi-9psi. The motor/turbos are all stock and running under original boost levels, so i don't think it has to do with turbo surge/flutter. unless somewhere there is a blocked pipe, but even if there is when the turbo sputter happens, it is relatively quiet. You feel it in the oscillating levels of torque more than you hear it. I will pull some of the pipes off though and see if there are any blockages for some reason

I'm still not fully convinced its not a significant boost leak. Anyone recommend any aftermarket coupling kits to replace the original ones from the turbos all the way to the intake plenum? I replaced the vacuum lines already, so really just need the couplers.
 

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Discussion Starter #7
built myself a pressure-test kit after replacing all the vacuum lines I could find. Holds pressure pretty well and I cant find any leaks, so I moved on to check fuel pressure, and everything seems normal in that regard.

However, I am starting to think that maybe one of the turbos (or both) is experiencing some issues. At low turbo rpm and low motor temps, the turbo's sputter all the way through till about 5k motor rpm but then smooth out for a full .7bar boost. Now once the vehicle warms up a bit and also if I keep the motor rpms 4-5K and the turbo spooling (just not under pressure), I can re-apply throttle and boost will build smoothly from 0bar-.7bar. I was going to drop thread of this explanation on a maintnenace/turbo thread and see what I come up with, but I'm assuming one of the turbo bearings are shot
 
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