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Old 05-26-2011, 03:24 AM
Registered User
Join Date: May 2011
Posts: 21
Help me diagnose my turbo

Hi kids, I have a 1980 300SD W116 with 400,000 miles. Replaced the motor 6000 miles ago with a much newer one. Before and after the swap, the turbo produced 3 PSI at highway cruise, up to 8 PSI on hill climbs at 3000 RPM.
I put a limiter valve into the turbo sense line between the manifold and wastegate.
I have never adjusted the wastegate. With the limiter valve, I could get boost as high as 25 PSI, but I adjusted it to get just 14 PSI on 3000 RPM hill climbs. It was perfect.
Suddenly, now it only goes to 4 PSI, still holding 3 at cruise. I removed the valve and went back to a straight line to the turbo, no change. I have not reinstalled the valve and tightened it down yet, to see if I can bring the boost back up, because I want to understand what is happening.
My pressure gauge Tees into the line just before the electric valve on the firewall that is supposed to limit boost to protect the tranny.

Of course, the gauge could be failing, or have a leak in the hose. What else could be going wrong? Sticking my hand in the end of the turbo, the shaft seems to have no play and spins freely.

So how do these degrade? Is a seal failing, or a bearing won't let it spin up fast? I just thought I should try with the air filter removed, it is fairly dirty and I can imagine that might be limiting, but the 4PSI limit seems to be absolute without the valve installed.

Do I rebuild the turbo, buy a rebuilt one? From who? Diagnostics I should try?
Appreciate your wisdom!
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Old 05-26-2011, 05:20 AM
Registered User
Join Date: Dec 2005
Location: Carson City, NV
Posts: 3,766
My first guess is that your wastegate spring has gone soft or something along those lines.
Anyone who thinks a 300D is fast drives too slow.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 351,xxx miles
08 Triumph Street Triple 21,xxx miles, lowered 10mm in front, Pirelli Angel GT tires, otherwise stock.
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Old 05-26-2011, 10:13 AM
scottmcphee's Avatar
1987 w124 300D
Join Date: Mar 2008
Location: Edmonton, Canada
Posts: 1,533
If you pull the wastegate hose off entirely, your boost should go to maximum that it can do.

If you can't get good boost in this position, then:
1. your wastegate valve is boogered (that's a technical term for cracked/open)
2. your turbo isn't compressing
3. you have a serious leak in the intake manifold so nothing is holding pressure
Scott McPhee

1987 300D
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Old 05-26-2011, 10:27 AM
Registered User
Join Date: May 2007
Location: Out in the Boonies of Hot, Dry, Dusty, Windy Nevada
Posts: 9,585
Welcome to the Forum, hope you stay for a long time.

This is the right place to get expert advice, go to the Junk yard and pull off a wreck.
That said, cheaper than a rebuilt one, and not all junk cars have junk parts. I have seen some good turbos in the PNP yards, and for around $60. the one on our 85 is no better or worse than what I see in the JY.

If it the waste gate as the problem, I guess it can be replaced. I haven`t seen them sold seperately.

Now back to the experts.

there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works
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