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Old 09-17-2016, 02:48 AM
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How to get great performance: W123 3000D turbo

Hi all, My California 1984 Mercedes Benz w123 turned 200,000 miles today 9/16/16; and I want to share how I have gained great performance with my w123 300DT. This car has been in my family for 31 years and has been a daily driver for my father, then my mother, who drove it until she was 91 years old and now in my possession for the last 5 years. It was a dog when I got it, peddle to the floor just to get it slowly going of the line. Here is what I did to get this back to life and possibly better than new performance even with 200,000 miles on the car. I received the car from my mom with 149,000 miles on it and it was really slow! (garaged every night of it's life). All service receipts since 1984 and fluids and maintenance completed on schedule. Lots of carbon buildup due to not having been driven more than 40 MPH for 15 years. Just a trip to the store and back home, no high speed or freeways at all for 15 years. Between the carbon buildup, sticky ring or rings, the ALDA & fuel pressure out of speck it really took time to get up to speed.

First things done: Compression test finding 406 PSI, all equal on all 5 cylinders! All 406PSI, incredible!!!

1. Oil Changed to Mobil1 15w50 Summer & Mobil1 TDT 5w40 Winter (changed every 5,000 miles)
2. Transmission fluid changed to Mobil1 ATF
3. All other fluids changed with appropriate fluids.
Adjusted the valves.
4. Several Italian tune ups.
5. 1 bottle Marvel mystery oil in gas tank (Yes it works!) but one time only.
6. 1 bottle Marvel mystery oil in the engine (Yes it works!) one time only. (I dumped the oil after 500 miles to get mystery oil out)
7. Origional Injectors rebuilt by local Authorized Bosch injector service.
A. Paid extra to have all injectors pop at exactly 135 BAR.
8. Cleaned the banjo bolt.
9. 1 bottle of Diesel purge run directly into the fuel pump.
10. EGR delete
11. Air recirculation valve (ARV) delete
11. A. Set the fuel pressure valve bolt spring on the back of the fuel pump to exactly 25mm. (It was too short and not providing enough fuel pressure)
12. Drove car for 3,000 miles Italian style as much as possible.
13. Oil Changed Mobil1 15w50 without mystery oil.
14. Verified no timing change stretch.
15. Reset the timing using the Mercedes Benz A-B light system method and then advanced the timing by just a small amount.
15. Cracked Open the ALDA and turned screw counter clockwise in small 1/8 steps for best performance without smoke off the line. The sweet spot was 1/2 turn CC for this car.
16. Solved all vacuum problems everywhere.
17. Set the transmission pressure regulator mounted on the transmission to stock for my model year. Set the transmission vacuum valve to achieve the range of 0 to 14 bleed off Pressure. I did not have to adjust the waste gate on the turbo as I have plenty of boost once I get to 1900+RPMs.
After getting rid of all the buildup carbon in the engine I was amazed at the performance. Honestly it drives like a gasser off the line and through out the entire power curve.

18. Pulled the head and ported the head to the manifold. High performance valve job including back cutting the valves. Now much more power through the entire power curve. Definitely more horsepower after the valve job and porting.

No adjustment done to the fuel injection pump at all it is stock.

The 1984 California 300D did not have any "Trap Oxidizer"

Results, unbelievable performance.
Mileage with A/C on 18- 20 town, 28 highway up to 75 MPH. A/C off 21 in town, 28 to 30MPG Highway straight and level up to 75 MPH.

It continues to be garaged at my home and is my daily driver. Everything works as it should and probably better than original. I have gone through just about every inch of this car to get everything right and It was a great and rewarding learning experience. I hope this post can be helpful to anyone wanting to get there w123 Diesel up to the best performance possible without messing with the Turbo waste gate or the stock injection pump internals.
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Last edited by mparis; 09-17-2016 at 02:41 PM.
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Old 09-17-2016, 08:11 AM
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i've always heard that carbon will raise your compression giving more power to a point.
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Old 09-30-2016, 01:54 PM
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Could you expand on your valve job details?
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Old 09-30-2016, 04:17 PM
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Old 10-16-2016, 03:56 AM
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Cant you turn down the injection pump to get better gas mileage?
Also l wonder if the porting is the culprit for the just about good gas mileage

I need 30mpg. With Ac on
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Old 10-17-2016, 12:06 AM
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Join Date: Oct 2016
Location: Houston
Posts: 60
Try a lighten crank pulley and maybe a little bit lower diff gear might be able to pull the city mpg up some "maybe",
also have you ever tryd messing with the shocks and springs to get a lower center of gravity, reducing body roll at take off, also making the car more aerodynamic?
I don't think itl make much difference in the city just a tiny bit.
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Old 10-17-2016, 02:14 AM
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You definitely wanna get it to 1000 rpms at 60mph
I believe you change the injection pump and duty cycle for 38-40mpg with a little power loss
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Old 04-11-2017, 01:08 PM
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What is an Italian Tune up

Please explain - What is an Italian Tuneup?

1984 300 D Turbo (3rd owner) 516,000 miles
Purchased in Houston in 2003
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Old 04-12-2017, 11:57 AM
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Originally Posted by carolbarnes20 View Post
Please explain - What is an Italian Tuneup?

1984 300 D Turbo (3rd owner) 516,000 miles
Purchased in Houston in 2003
The "italian tune up" is slang for running the car very fast to get the engine rpm and temps high- thus "burning" off any residue and built up carbon. If your engine is otherwise healthy this is a common tactic with all diesels to improve daily performance; run them at full load for a spell. In marine diesels it's as long as 10-15 minutes at wide open after a day of cruising.
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Old 04-13-2017, 02:05 PM
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Location: Northern,Ca
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Originally Posted by Anthony's View Post
You definitely wanna get it to 1000 rpms at 60mph
I believe you change the injection pump and duty cycle for 38-40mpg with a little power loss
Not my kinda thing. Something will wear out prematurely. driving a car at 1000 is not right. I would never do that to my gearbox, especially an overdrive, Not to mention lower end of the motor will likely stress as well. The fuel savings are not worth the repair costs IMHO. 45-60 in overdrive is too low. These cars are suitable for the autobahn.

84 280sl
82 300d euro
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Old 04-26-2017, 01:52 PM
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Would be nice to have a baseline 0-60 time, and then re-test with each step to document the improvement.

What is 0-60 time now?
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
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