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93 turbo wastegate ?

ak diesel driver

ak diesel driver

6.5 driver
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So a buddy of mine recently picked up a 93 6.5 . My understanding is the wastegate is mechanical so here comes the ? Why does the boost fall off very similar to the PCM controlled ones? It will hold about 7-8 lbs and then when the rpm and load increases it will fall off to around 5 lbs.
 
My only guess would be there's a certain tensioned spring inside. I have the wastegate solenoid bypassed in my 97' so the vacuum is right to the actuator. It will bleed off just takes a little more pressure, But when I'm cruising down the highway ill hold steady 5-6lbs. When I bought my wife's wrangler then other weekend on the high way back with the trailer loaded I stayed 7-8lbs. It ran great.
 
I agree with sctrailrider. If you notice that the boost falls off and you have more black smoke then the problem might be a turbocharger. Generally though the boost follows the amount of fuel up to the point the wastegate opens or you run out of turbocharger. It may be possible that the wastegate shaft is sticking as well. If it has gotten rusty or contact with the shaft somewhere.
To test you could add a spring or otherwise wire it shut and see if it does the same thing. If it does then it for sure would be an IP problem.
 
I would suggest tie the gate closed and see, but if it's a stock IP I bet it's on the defuel side of the ramp.... what rpm are you seeing the boost drop??
 
ak diesel driver said:
2500+
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Because the turbo has reached its "choke point" for flow on the exhaust side at 2500 rpm and drive pressure is causing the wastegate to open. Wired shut won't make a difference because that too small exhaust housing on the GMx will still "choke" at 2500+ and you won't see any noticeable improvement.
 
Husker6.5 said:
Because the turbo has reached its "choke point" for flow on the exhaust side at 2500 rpm and drive pressure is causing the wastegate to open. Wired shut won't make a difference because that too small exhaust housing on the GMx will still "choke" at 2500+ and you won't see any noticeable improvement.
Click to expand...

I have the truck manifold setup on my new engine sitting on the test stand. Just for testing you understand. No load so the turbo gm4? just spins but man it looks like a restriction just sitting there. So tiny compared to the new hx40 and the s300? that is sitting in my van. Not sure why GM had to make them so small. And that manifold. I can't decide whether that was some kind of genius or the craziest thing I ever saw. Definitely think some improvements could be made there.
 
The computer tries to mimic the mechanical system like a TBI did a carburetor. In theory the WG is supposed to open during light load cruise with the computer system. The computer system has delays built in so it's slow to respond.

With a turned up 6.2/6.5 pump and turbomaster screwed tight there is no reason you can't run the turbo into overspeed at 14+ PSI. My 1993 with a Turbomaster Set at 12 PSI at 1000' will climb 2 PSI into overspeed at 8000' altitude.

The mechanical 1993 system itself doesn't care about the boost number. It's limiting the turbo biased solely off drive pressure. So the boost number can vary depending on load because it's not monitored by the 1993 setup.
 
Wasn't there something about the early GM turbo's that the waste gate pivot shaft would wear and cause variations in boost?

But I think the waste gate is just opening slightly and general choking at high rpm. An adjustable turbo master might help.
 
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