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2008 Mercedes R320 diesel. Rail pressure too high. Limp mode…

Customer Question
2008 Mercedes R320 diesel. Rail pressure...
2008 Mercedes R320 diesel.
Rail pressure too high. Limp mode activated.
Components checked and changed as follows.Changed: Y94 Quantity control valve,Y74 Pressure control. Includes rail.
Complete HP pump and drive mounting assembly from known good vehicle. No change.
note Pump assembly from problem car fitted to donor car ran correctly.
One fuel injector. Over correction issue corrected.
New fuel filter.
Checked.
Wiring integrity between all fuel valve and sensors and ECM. Found ok.
Low pressure pump performance. Pressure and low ok.
Fuel return flow no restriction.
MAP and charge pressures correct.
Submitted: 8 months ago.Category: Mercedes
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Answered in 31 minutes by:
12/3/2017
Mercedes Mechanic: Todd M, ASE Certified Technician replied 8 months ago
Todd M
Todd M, ASE Certified Technician
Category: Mercedes
Satisfied Customers: 1,902
Experience: Technician at Montgomery Motors
Verified

Hello. My name is ***** ***** I will be assisting you today. I see that you have replaced various component with no results. This is because the issue that you are having is likely due to the CDI control unit. This component is responsible for fuel supply control. If this component is faulty, then the readings of the system will be off causing the problems that you are experiencing. In order to confirm this, testing will need to be done. Although, you have already replaced most of the components that could cause this issue. Here, I am attaching description and operation along with the electrical information for the circuits to give you a visual. The areas of concern are highlighted. Have you scanned the vehicles for codes? If so, do you have them on hand so that I may check for testing information?

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Mercedes Mechanic: Todd M, ASE Certified Technician replied 8 months ago

Here, I am attaching location and replacement information for the control module along part and labor pricing. Part pricing is from the manufacturer. Labor pricing is listed in hours and depends on the hourly rate of the shop.

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Mercedes Mechanic: Todd M, ASE Certified Technician replied 8 months ago

.

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Mercedes Mechanic: Todd M, ASE Certified Technician replied 8 months ago

If you require more information on this issue and/or are not satisfied, let me know, please, and I will attempt to assist you further on this. I hope this information points you in the right direction. If you have any further questions or concerns on this issue, feel free to ask. If you are satisfied, and have found this information helpful, a positive rating would be greatly appreciated and necessary in order for experts to receive credit for answers provided. Thank you.

A positive rating does not close the session. We will still be able to communicate, and I will still continue to assist you with this issue as needed.

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Mercedes Mechanic: Todd M, ASE Certified Technician replied 8 months ago

Just as a reminder, if you have found this information helpful, please do not forget to rate the service. Thanks again.

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