VAG common rail starting/running issues

Damon Technical Support Specialist Wheatley, United Kingdom Posted   Latest  
Tech Tip
Driveability
P0087 - Fuel Rail/System Pressure - Too Low Bank 1
P1065
P310B

Symptoms

1. Non start, lack of power, juddering engine, poor running, fuel pressure and/or deviation fault codes logged

Faults

P008700 

Rail Pressure below limit Engine Control Module - Engine Control Module 

P106500 

Fuel pressure regulation system deviation Engine Control Module - Engine Control Module 

P310B00 

Fuel low pressure regulation fuel pressure outside tolerance Engine Control Module - Engine Control Module 

Possible Causes

1. Lack of low fuel pressure

2. High pressure pump

3. Engine control unit

Repair Steps

1. How it works:

The high pressure is generated by the high pressure pump which is controlled via the fuel metering valve (N290) on a demand based PWM signal, the high pressure pump generates too much fuel pressure, the pressure is then controlled via the fuel pressure regulator valve (N276) in the end of the rail by discharging excess fuel back into the return. (if this is removed from the rail it has to be replaced). Connect your Assist Plus unit, communicate to the Engine Electronics Control Unit, go into dynamic requests, find the live data for rail pressure, there should be specified and actual rail pressure, Compare the readings and do the pressures relate to the fault code you have for low pressure or deviation? 

2. Non start/Low fuel pressure:

If you only have single figure bar of fuel pressure in the rail this would indicate that you have low pressure to the high pressure but high pressure is not being generated. You will need to check you have a good constant low pressure supply to the high pressure pump (between 3.5-7 bar depending on engine). Then remove the fuel metering valve (N290) from the high pressure pump (be careful not to damage the seal) and inspect inside for any swarf, if there is swarf then a major repair is needed of the complete fuel system. If nothing is in there and the fuel quality is good then this would indicate a potential issue with the high pressure pump not generating the high pressure into the system or a controlling problem. 

3. Fuel pressure regulation code:

If your high fuel pressure live data is jumping considerably up and down this would be the reason for the code due to the pressures being outside the controlled deviation values. You will need to check you have a good constant low pressure supply to the high pressure pump (between 3.5-7 bar depending on engine). If this is ok then remove the fuel metering valve (N290) from the high pressure pump (be careful not to damage the seal) and inspect inside for any swarf, if there is swarf then a major repair is needed of the complete fuel system. If nothing is in there and the fuel quality is good then this would indicate a potential issue with the high pressure pump not generating the high pressure into the system constantly, regulating valve (N290) or a controlling issue. 

+2
Maurice Business Development Manager
Geebung, Australia
Maurice
 

I find the best way to rule out the low pressure side of any common rail diesel is to run a separate fuel supply to the high pressure pump. I have a little axillary fuel tank with pipes going to the pump and another pipe going back returning fuel back to the axillary fuel tank, I use clear plastic pipes so if any air is returning to the tank it will be easily noticed. I can sit my axillary tank inside the floor of the car and go for a good road test if I have a intermittent problem. This is the quickest and most effective way to totally rule out the low pressure side of the common rail system. I bought this axillary fuel tank set up from Clinton Brett who runs Diesel help Australia dieselhelp​.​com​.​au but you can easy make up your own.

+2 Ð Bounty Awarded
Michael Owner/Technician
Cartersville, Georgia
Michael
 

That's a good idea to take off N290 to check for metal. I have one with metal in the filter and I expect to see it there too!

0 Ð Bounty Awarded