1991 300D.. Bad Turbo? - PeachParts Mercedes-Benz Forum

MeinGreaseCar · #1 07-24-2018, 11:04 AM

I have a 1991 300D. I got it about 5 years ago with 27k on it. Very unmolested car.

Over time my performance seemed to slip... I decided to finally get after it.

I fabbed up a Block of plate for the EGR. Put on a temporary boost gauge and got to work.

I saw virtually no boost until 3k rpm. Then it would build to about 6lbs. I could get it to show 8lbs with WOT in second or third.

Put in a manual boost controller. I saw similar performance as I was adjusting it, I saw a very slight increase... then once the car was warm.. I wasn't even getting the 8lbs I saw at first.

Thoughts? Time to send the turbo out for an overhaul?

Thanks

JP

tjts1 · #2 07-24-2018, 11:13 AM

It has a vacuum actuated waste gate. Apply vacuum to keep it shut then test the boost.

vstech · #3 07-24-2018, 01:49 PM

Fuel filters?

Mxfrank · #4 07-24-2018, 06:40 PM

EGR removal is just an idiotic idea. It has next to no impact on performance or economy. About the only advantage is that you won’t build soot in the manifold and won’t have to clean it out every 200k miles or so.

Clean your ALDA port and the odds are you will find your mojo.

2for1 · #5 07-24-2018, 07:09 PM

I had the same issue on an 87 300d. Ended up being a clogged catalytic converter.

Cleaned it out and turbo works fine. Engine needs to breathe.

tjts1 · #6 07-24-2018, 07:11 PM

Quote:

Originally Posted by Mxfrank

EGR removal is just an idiotic idea. It has next to no impact on performance or economy. About the only advantage is that you won’t build soot in the manifold and won’t have to clean it out every 200k miles or so.

Clean your ALDA port and the odds are you will find your mojo.

LMFAO
I'll race you.

MB140300SD · #7 07-24-2018, 11:14 PM

The turbo on these is vacuum operated. If there is any leak at all under the hood it will affect boost. Also, if you have a bad sensor somewhere, such as a rack position sensor, the computer will put it in "limp mode" and vent all the boost. I am trying to remember if disabling the EGR on those also puts it in limp mode.

dieselbenz1 · #8 07-25-2018, 12:05 AM

Read your codes and reset them.

MeinGreaseCar · #9 07-31-2018, 08:04 PM

Thanks for the tips.

I'm holding off on pulling the turbo. I've been having some odd starting issues. I did fuel filter recently, and well as replacing the lift pump (no changes)

It will start fine when cold. It will start up fine immediately after shutdown.

When it's sat 30 to 90 minutes.. I have a hard time starting. It's acting fuel starved. I can stomp the accelerator down, and with some excessive cranking.. get it to fire and then it's fine. I have tried to open the fuel cap.. just to see if the vent was blocked, and it was pulling a vacuum on the tank. No change.

I've planned to have the mechanic look at the exhaust path. I've got a new set of injectors coming. I'm also having him spend some time looking over the vacuum system. I've had for quite a while a bit of nailing. Not bad, but I just don't think it sounds as smooth as it should.

As for the EGR.. I find it has NO redeeming qualities. I fabbed up 'block off' plate. It can sit there and do it's thing.. none of the exhaust is going to head back into the intake.

Thanks. I'll keep you posted.

JP

MB140300SD · #10 07-31-2018, 10:14 PM

Here is a quick way to test to see if its the turbo or not. Just run a vacuum line directly from one of the branches of the big line off the pump to the waste gate. Drive it, see if it has tons more power or not. Do not leave it this way.

ROLLGUY · #11 07-31-2018, 11:22 PM

Quote:

Originally Posted by MB140300SD

The turbo on these is vacuum operated. If there is any leak at all under the hood it will affect boost. Also, if you have a bad sensor somewhere, such as a rack position sensor, the computer will put it in "limp mode" and vent all the boost. I am trying to remember if disabling the EGR on those also puts it in limp mode.

I agree. I had a similar problem with a '91 300D W124 I used to have.

MeinGreaseCar · #12 08-13-2018, 05:52 PM

Appears I have a bad wastegate actuator. The mechanic said it wouldn't hold vacuum or boost. I'm Not sure if it's stuck, or if it's only got a ripped diaphragm.

Unfortunately, the actuator isn't part of the turbo overhaul. Been researching a few threads on changing out the vacuum operated wastegate.

JP

shertex · #13 08-13-2018, 05:58 PM

Quote:

Originally Posted by MeinGreaseCar

Appears I have a bad wastegate actuator. The mechanic said it wouldn't hold vacuum or boost. I'm Not sure if it's stuck, or if it's only got a ripped diaphragm.

Unfortunately, the actuator isn't part of the turbo overhaul. Been researching a few threads on changing out the vacuum operated wastegate.

JP

This would be a great time to switch to a pressure actuated wastegate. Perhaps that's what you mean.