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Discussion Starter · #1 ·
Apparently my turbo is giving me -1psi of boost...

The saga:
Installed a Glowshift boost gauge, and on first start noticed that it didn't appear to work, the needle would actually drop instead of go up.
I did some testing and figured out that the vacuum pump wasn't vacuuming. I had already purchased a manual wastegate control in my planned DB2 conversion so I went ahead and installed it on my turbo, the result of which is -1psi of boost... no change. I grabbed another pressure/vacuum gauge and it showed the same.

Taking the boot off the front I can see the turbo spin while the engine runs, there are new exhaust manifold gaskets and crossover pipe gaskets (along with a new left exhaust manifold) so I'm sure there isn't an exhaust leak causing the issue. The turbo wheel spins nicely and isn't loose so I don't think the turbo internals are bad or seized, and the fins on the intake side look ok (dirty but intact, no damage of any kind visible). I can put a board over the turbo intake opening and kill the engine so I'm fairly sure there isn't an intake manifold leak, and when doing that my vacuum gauge shows a good vacuum so I'm sure it works (and I can puff into it and move the needle so I'm sure positive works).

So, the only two possibilities I can think of:
#1: The turbo is completely and totally shagged, spins but produces nothing.
#2: My tap location for the boost gauge is bad. I put it in the center of the 'cup' in the middle of the intake manifold thinking that would be a good spot, but it's entirely possible that with the air rushing around that actually sees a vacuum under light load?

Any words of wisdom from the masters out there?

Video I made of the question:
 

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Try cranking down the controller spring down till you see 1-2 psi. on the gauge
 

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Discussion Starter · #3 ·
Ok, so the turbo might not be as completely shagged as I thought... or that pocket is still not showing the full boost... not sure.

I took it for a drive and under load (accelerating hard up a hill, best I could do) the boost will peek out at around 8.5/9psi. Running around town it still shows 0 or -1 psi, only when accelerating does it show anything.

I don't want to over crank the boost control, just in case the gauge is under-showing by a few PSI, this engine isn't in the best shape and I really don't want to blow a head gasket feeding it 15 or 20psi while my gauge is only showing 9 or 10.

Also, on the drive I'm actually hearing a whistle that might be the turbo working, which I hadn't noticed before (probably because the vacuum pump wasn't working keeping the turbo from actually doing anything). So it might be running better, but until I get some kind of confirmation that the location isn't giving me a false reading I'm not going to push it any farther.
 

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1995 GMC Suburban
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18,370 Posts
Ok, so the turbo might not be as completely shagged as I thought... or that pocket is still not showing the full boost... not sure.

I took it for a drive and under load (accelerating hard up a hill, best I could do) the boost will peek out at around 8.5/9psi. Running around town it still shows 0 or -1 psi, only when accelerating does it show anything.

I don't want to over crank the boost control, just in case the gauge is under-showing by a few PSI, this engine isn't in the best shape and I really don't want to blow a head gasket feeding it 15 or 20psi while my gauge is only showing 9 or 10.

Also, on the drive I'm actually hearing a whistle that might be the turbo working, which I hadn't noticed before (probably because the vacuum pump wasn't working keeping the turbo from actually doing anything). So it might be running better, but until I get some kind of confirmation that the location isn't giving me a false reading I'm not going to push it any farther.
I think that is normal behaviour.
 

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1994 K2500 Suburban 6.5 turbo.
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Boost bolt is what I used to install my boost sensor. Take out the middle rear top hat bolt and replace with a boost bolt works great. I run anywhere from 5 to 9 ish lbs up long hills or accelerating hard. Around town boost is normaly 1 to 4 psi.
 

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Discussion Starter · #6 ·
Boost bolt is what I used to install my boost sensor. Take out the middle rear top hat bolt and replace with a boost bolt works great. I run anywhere from 5 to 9 ish lbs up long hills or accelerating hard. Around town boost is normaly 1 to 4 psi.
I actually purchased one of them, but for whatever reason it's too short, isn't even long enough to engage any threads.
 

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Premium Member
1995 Chevrolet Silverado Z71 6.5 TD
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632 Posts
Maybe they sent you the wrong part.
 

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Discussion Starter · #8 ·
Maybe they sent you the wrong part.
That or the intake changed between the 94 and 97+, I found out buying oil cooler lines that the previous owner had swapped the engine at some point to a later model engine.

Either way, I had been purchasing parts ahead of doing the work so by the time I found that out it was too late to return.
 

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1995 Chevrolet Silverado Z71 6.5 TD
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632 Posts
Get the engine number of the rat rear of the block if you haven’t already.
 
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