300SDL Power Loss
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Joined: Jun 2008
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300 SDL
300SDL Power Loss
The car has significant power loss in drive, but not in neutral or park. The mechanic at Don Pool (Arlington VA, USA) replaced primary and secondary fuel filter, he empty the tank to check algae and the problem still exist. Don Pool mercedes said it could be injection pump but they were not sure.
The Car has 129000 miles
1)Checked the ohms/voltage at control rod travel sensor, they seemed to match the specs.
2)Checked the air flow sensor ohms/voltage and the movement of the air flow sensor plate, they seemed to match the specs and the plate was moving without resistance.
3) Checked the EGR valve by applying vacuum, it did not made audible sound so the EGR valve was replaced with OEM unit. While replacing EGR valve, one thing was noticed that there was lots of soot/black carbon buildup in the pipe between EGR valve and trap oxidizer unit.
4)Replace air filter with OEM unit.
5) Check the fuel pump for quantity of delivery, it delivered ~150 cubic cm in 30 sec, which matched the specs.
One thing I did notice, that the waste gate valve does not open. I don't know this would impact the power loss.
In addition, dealer spent 2 hours diagnosing the problem but they did not gave me any conclusive answer. They guessed it is a bad injection pump.
History: Injection pump seals were replaced (6 months ago), during this work mechanic checked the injectors, as per him injectors are good.
Conclusion: The car still has significant power loss. I am so confused about this power loss. Any help or hints will be greatly appreciated.
The Car has 129000 miles
1)Checked the ohms/voltage at control rod travel sensor, they seemed to match the specs.
2)Checked the air flow sensor ohms/voltage and the movement of the air flow sensor plate, they seemed to match the specs and the plate was moving without resistance.
3) Checked the EGR valve by applying vacuum, it did not made audible sound so the EGR valve was replaced with OEM unit. While replacing EGR valve, one thing was noticed that there was lots of soot/black carbon buildup in the pipe between EGR valve and trap oxidizer unit.
4)Replace air filter with OEM unit.
5) Check the fuel pump for quantity of delivery, it delivered ~150 cubic cm in 30 sec, which matched the specs.
One thing I did notice, that the waste gate valve does not open. I don't know this would impact the power loss.
In addition, dealer spent 2 hours diagnosing the problem but they did not gave me any conclusive answer. They guessed it is a bad injection pump.
History: Injection pump seals were replaced (6 months ago), during this work mechanic checked the injectors, as per him injectors are good.
Conclusion: The car still has significant power loss. I am so confused about this power loss. Any help or hints will be greatly appreciated.
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Joined: Sep 2011
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2011 VW Golf TDI
SOLUTION
Boy o Boy. This issue is THE main problem that occurs on all 300sdls EVENTUALLY. And, after doing some troubleshooting on my own, and talking to 4 different mechanics here in Phoenix, AZ, to confirm, I think I can safely say that I have solved the problem. The problem is related to the ALDA but is not the ALDA itself. The problem is worn out/corroded/leaking/spongey black rubber vacuum lines that are associated with the ALDA and are found secured next to an ALDA RELATED SENSOR which is bolted to the firewall on the upper right side of the engine bay (vacuum lines running from the ALDA attach at directly above and below the sensor). These two black rubber vacuum line tubes are about 1.5 inches long, 1cm thick and link the sensor to the clear/white plastic vacuum tubes that run to the ALDA. These tubes QUICKLY and ALWAYS break/corrode due to the heat and pressure of the system. Once they become more pliable and putty-like (or leak) they tend to disrupt vacuum signals by flexing and expanding with vacuum pressure. This SMALL but VERY IMPORTANT aberration throws off the whole precise and delicately balanced ALDA vacuum feedback system. This is clearly a design defect by mercedes benz. Just replace those two black rubber tubes leading to the ALDA's engine bay mounted sensor and in 99% of cases it fixes the problem. Thanks guys, I hope I have helped!
Newbie
Joined: Sep 2011
Posts: 2
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2011 VW Golf TDI
P.S.
NOTE: most people over look these specific vacuum tubes either because they don't seem important to the system or because they mistakenly think that the soft, and pliable or cracky texture of these line was designed to be that way and is normal. But this is not the case. The vacuum lines in this part must be as airtight and as STIFF as possible (it is a very precise and sensitive vacuum system). Thanks!
