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  #1  
Old 06-24-2007, 12:10 PM
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Question 350 turbo question

I just put a head gasket on my 90 350 SDL at 197k. The bores are still round, head flat, valves good, compression on cly's high end of good range all within 5 psi of each other. The car has always seemed to lack power on accel. Cruises fine and mpg is within specs. I checked the boost pressure and the must I could get was 9 psi. Book says should run to 14. I pulled the turbo, bought a rebuilt kit for $110 (seals and bearings). The waste gate looks fine. I still only get 9 psi but did solve seal leak problem. The disk is spinning at idle and spools up, waste gate is closed. What is the problem? All I can think of is inlet or exhaust system blockage but all is stock and inlet is not blocked. Really don't want to pull exhaust. If boost was running to 14 psi I would probably find my missing power. Ideas?

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Old 06-24-2007, 01:28 PM
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Maybe the wastegate is set at 9 psi. Disconnect the wastegate hose and drive it with the boost gauge attached.........be careful.
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Old 06-24-2007, 01:41 PM
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What's the 0-60 time? Maybe your expectations are too high.

Does your turbo have an ARV? If so maybe it's leaking.

Are cam and IP timing within spec?

Clean fuel filters?

Sixto
93 300SD 3.0 - comatose
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Old 06-24-2007, 03:35 PM
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Waste gate never opens. Checked it with regulated pressure, starts to open with 14 psi.
Whats an ARV?-nothing on turbo but waste gate. Replaced cam when I did head gasket. IP timing 14.5. Filters all replaced. I'm stumped!
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Old 06-24-2007, 03:46 PM
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Quote:
Originally Posted by loneranger View Post
All I can think of is inlet or exhaust system blockage but all is stock and inlet is not blocked. Really don't want to pull exhaust.
If the wastegate is working properly, the next possibility is the exhaust. Does the '90 have a catalyst of any type?

The '87 has a catalyst and I suspect it's partially plugged. It's time to 60mph is a full two seconds slower than the '86 without the catalyst. Additionally, the '87 has a new head with angled prechambers..........there's NFW this vehicle should be this slow. The SD will run the exact same time to 60 mph.
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Old 06-24-2007, 04:40 PM
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Next thing I'd do is remove the ALDA.

Are you sure the wastegate is fully closed? No cracks in the flap or seat? Flap is centered on the seat?

Sixto
93 300SD 3.0 - comatose
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Old 06-25-2007, 01:31 AM
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Next thing I'd do is remove the ALDA.
Yes, I agree. That's faster than dealing with the exhaust and will confirm or rule out a non-functional ALDA.
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Old 06-25-2007, 07:26 AM
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Already checked the ALDA. It does have angled prechambers. Thanks for the heads up on the exhaust. Next time I get a chance I'll disconnect the coupler and run a flex pipe off the turbo exhaust and see if that does the trick. Thanks again for all the info. Al
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Old 06-25-2007, 09:05 AM
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Already checked the ALDA.
Please explain, in detail, how you checked it.

Without removing it, it's not easy to verify it's proper function, or lack thereof.
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Old 06-25-2007, 04:13 PM
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Quote:
Originally Posted by loneranger View Post
Waste gate never opens. Checked it with regulated pressure, starts to open with 14 psi.
Whats an ARV?-nothing on turbo but waste gate. Replaced cam when I did head gasket. IP timing 14.5. Filters all replaced. I'm stumped!
An ARV is an Air Recirculation Valve. It basically dumps air that the compressor wheel has compressed back into its intake. It usually is located on the outlet of the compressor housing. Your 350 should have one. It is used to limit/control the boost level of a turbo for certain engine operating conditions. It is mainly used a for meeting emissions or keeping other emissions equipment functional. For diesels without an oxidation catalyst or oxidizer trap its used to increase EGR flow by dropping the boost in the intake manifold while keeping exhaust manifold pressure high. For vehicles with an oxidation catalyst or oxidizer trap it is also used to keep boost low to make EGTs higher to help the oxidation catalyst or oxidizer trap function at low power output levels.

I have found that when adjusting a waste gate opening pressure it can't be checked unless on the road. The reason is that the back pressure created by the turbine also helps push the waste gate open to some degree.
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  #11  
Old 07-01-2007, 11:29 AM
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this car has no ARV on it. there is one on my 300CD so I know what your talking about. Pulled ALDA off to check. I have not checked to boost while driving so will try that. thanks

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