Need advice on what my turbo is doing - PeachParts Mercedes-Benz Forum

lombrozo · #1 06-07-2011, 06:56 PM

Hi kids. I have a 1980 Mercedes 300SD W116. Before I put a pressure regulator valve in the boost controller line, it would peak at 8PSI.

With the control valve, at first, it would boost up to 25 PSI, so I backed it off and had it perfect, peaking at 14 PSI on long hill climbs.
Then it changed. Now it still carries 3 PSI at cruise, all seems normal, but it peaks at 6 PSI. I tried removing the valve, still peaks at 6. I pinched the hose with vice grips, same 6 PSI.

Did I blow an exhaust gasket? Intake gasket? I don't hear any strange noises, but my hearing is not great.
Is my turbo leaking internally and unable to bring up enough pressure?
Is it turning too slowly?
Is the wastegate unable to hold closed against the pressure?
The car is running fine, otherwise. No smoke.

What next? I see articles where people are rebuilding for $50.
I see rebuilders for $300.
The only junkyard parts I have found so far are in the $200 range, and of course who knows the quality?

Looking for diagnostic suggestions, if I don't need a new turbo, or advice on rebuilding myself or good sources for reliable used turbos.

I have been told that this is a Garrett T3 and interchanges with any 300D or 300SD from 1978 through 1984. Is that true?

Thanks, appreciate the help.

leathermang · #2 06-07-2011, 07:23 PM

Quote:

Originally Posted by lombrozo

..... The car is running fine, otherwise. No smoke.....

So, if you close your eyes so you can not see those gauges.. the car is just FINE ?
LOL,
Close your eyes... you are watching your car too closely...
A strange set of symptoms showing...
Has your mileage been affected either way ?

layback40 · #3 06-07-2011, 10:33 PM

Quote:

Originally Posted by leathermang

So, if you close your eyes so you can not see those gauges.. the car is just FINE ?
LOL,
Close your eyes... you are watching your car too closely...
A strange set of symptoms showing...
Has your mileage been affected either way ?

Leathermang.
Do you do this when you are headed for a tree or power pole?

Gotya !!!!

With all the changes that have been made, its likely that the waste gate is no longer set correct.

leathermang · #4 06-07-2011, 10:41 PM

No, I do this before I head towards a tree or light pole. But I do not see them coming so it does not bother me during the transit time.

Codifex Maximus · #5 06-07-2011, 11:52 PM

Quote:

Originally Posted by lombrozo

Hi kids. I have a 1980 Mercedes 300SD W116. Before I put a pressure regulator valve in the boost controller line, it would peak at 8PSI.

With the control valve, at first, it would boost up to 25 PSI, so I backed it off and had it perfect, peaking at 14 PSI on long hill climbs.
Then it changed. Now it still carries 3 PSI at cruise, all seems normal, but it peaks at 6 PSI. I tried removing the valve, still peaks at 6. I pinched the hose with vice grips, same 6 PSI.

Did I blow an exhaust gasket? Intake gasket? I don't hear any strange noises, but my hearing is not great.
Is my turbo leaking internally and unable to bring up enough pressure?
Is it turning too slowly?
Is the wastegate unable to hold closed against the pressure?
The car is running fine, otherwise. No smoke.

What next? I see articles where people are rebuilding for $50.
I see rebuilders for $300.
The only junkyard parts I have found so far are in the $200 range, and of course who knows the quality?

Looking for diagnostic suggestions, if I don't need a new turbo, or advice on rebuilding myself or good sources for reliable used turbos.

I have been told that this is a Garrett T3 and interchanges with any 300D or 300SD from 1978 through 1984. Is that true?

Thanks, appreciate the help.

You might take some pictures of your current setup OR draw us a diagram of your waste gate system/boost guage.

Have you tried to remove your ducting in a clean area and observe your clean air side of the turbo spooling up? And at what RPM it's doing it?

I don't have any guages for turbo boost at all. I just know it's working when it throws my head back during acceleration.

Hmmm... Have you checked the banjo bolt and tube that goes to the ALDA?

scottmcphee · #6 06-08-2011, 10:37 AM

Wastegate is probable, but maybe you're overfocussing on "the turbo". Don't forget that turbos respond to power curve by making more power, it's infectious. But what I'm getting at is if your FUEL is constricted you won't be making power, and you won't get your max boost. Sort of a self limiting prophecy. Ensure fueling is adequate.

I have a manual boost controller, set for 1 bar.. and got there when pressed hard. But when my ALDA burst its bubble (for the last time!) my boost dropped to about 1/2 bar, like you, pedal fully pressed to the metal, that was it. Car dogging around. So I popped the ALDA off and filed it in the circular bin, and BOOM! Back comes the boost and I'm head snappin' around town again.

lombrozo · #7 06-09-2011, 07:16 PM

My setup is simple, completely stock but with a limiting valve in the turbo sensing line and boost gauge in the line that goes to the overpressure switch on the firewall.

How do I diagnose an ALDA failure? I will check the banjo and lines. Is there a diaphragm inside that fails?

I really can't get more than 6 PSI out of a system that was happy at 15, and would easily go to 25, a couple weeks ago.