Power issues - 1985 Mercedes 300D Turbo Diesel - PeachParts Mercedes-Benz Forum

marco5 · #1 09-27-2017, 03:09 PM

Car: 1985 Mercedes 300D Turbo Diesel, non cali model

Mileage: 400,000-500,000KM

Other information: Original turbo has never been removed. I can't see a trap oxidizer so I don't think my car had one. Very well maintained car with regards to all tune up items for this model.

Hi there,

I'm experiencing some issues on my 1985 Mercedes 300D Turbo Diesel with regards to power (non cali model). The car has proper valve adjustment, fuel filters, compression etc so I've been digging into the engine quite a bit.

I hooked up a boost cable the other day and I'm getting 0 with the pedal to the floor. I also hooked up a vacuum tester to various components and noticed that the EGR is leaking and not holding pressure. It holds pressure for maybe 1-2 seconds and then it drops to 0. Could this be where the boost from the turbo is being lost? Could a broken/leaking EGR diaphragm cause this? Will simply disconnecting the vacuum cable and plugging it resolve the EGR problem?

I've heard that these turbos pretty much last the life of the car, is that true? Should I pull the turbo at this point and have it rebuilt?

Sorry for all of the questions, I'm not a pro like you guys and don't want to just toss money at the car but properly diagnose and fix it!

Regards,
Marco

SD Blue · #2 09-27-2017, 05:09 PM

Where are you taking the measurement for boost?

Typically, the lines for the pressure get clogged, especially with an operational EGR valve, and you get no boost to the Alda and no fuel enrichment.

Check the line that goes from the back if the intake manifold to the overboost protection valve and then to the Alda. You may need to remove and clean the banjo fitting and bolt at the back of the intake manifold.

greazer2b · #3 09-27-2017, 05:34 PM

Quote:

Originally Posted by SD Blue

Where are you taking the measurement for boost?

Typically, the lines for the pressure get clogged, especially with an operational EGR valve, and you get no boost to the Alda and no fuel enrichment.

Check the line that goes from the back if the intake manifold to the overboost protection valve and then to the Alda. You may need to remove and clean the banjo fitting and bolt at the back of the intake manifold.

I have a 85sd (Cali) had issues in past.Cleaned the line from over boost switch on intake, R&R turbo, intake, rebuild turbo, Egr delete from RollGuy, then replace Large O Rings on intake tube between turbo and intake manifolds.
That was the biggest culprit O Rings were hard, if you replace DO THE MERCEDES O RINGS...THE GREEN ONES the others aren't worth a hoot.
If you take it this far make sure you REPLACE THE STUD NUTS that hold the manifold to block they are one time use, pick up on another website not sold by our sponsor here

Did all that never had a problem, mine is a Cali model but I put on the Trap Oxidizer ByPass kit from RollGuy And haven't looked back.

greazzer2b

marco5 · #4 09-27-2017, 06:21 PM

Thanks everyone. I just did a very thorough inspection and noticed that the line coming from the banjo bolt and going to to driver side firewall has a very large crack in it. I will replace all lines and hoses, orings tomorrow. I don't know how I missed this.

I KNEW it wasn't the turbo.

BillGrissom · #5 09-29-2017, 03:31 PM

For those with a 1985 CA engine, also check that the turbo's compressor wheel isn't clogged with oil gunk. Those cars route oil in the blow-by directly into the turbo. Of course, that could affect earlier engines if blow-by oil gets past the oil catch can.