The Peugeot 307 2.0 HDi came into the workshop with a history of failed repairs and an inventry of second hand parts fitted in an attempt to get it running correctly.
We have identified the ECU as the culprit, the internal earth path for the rail pressure sensor has failed.
With the ECU repaired, we could consider what has caused the rail pressure to increase without any command from the ECU.
The engine would start and idle but it would cut out when the rail pressure exceed set limits. (400+ bar)
We monitored the current drawn by the pressure regulator during the pressure increase and it did not alter.
This means the increase in pressure is down to a mechanical fault, not an electrical fault.
All high pressure fault diagnosis must start with the low pressure system.
In this case a higher low pressure could possibly result in higher, high pressure values.
A gauge was set up to monitor the low pressure, and an oscilloscope analysed the high pressure voltage from the rail pressure sensor. (Remember the original fault affected this sensor)
The engine was started and the rail pressure settled to a even 1.3V with a low pressure supply of 4.5 Bar.
Then the engine cut out. The Supply pressure remained constant however the rail pressure increased at the time the engine cut out.
The return lines were checked for damage and they all appeared to be fine, so what is causing the rise in rail pressure?
This is where system understanding is key to the diagnosis. The pressure is regulated by a valve, this valve allows fuel to bleed past to reduce the pressure. It has a spring inside that holds around 80-100 Bar in the rail when there is no current flowing to increase this pressure by means of an electro-magnet forcing the valve closed. A cranking check using live data showed the pressure was in excess of 120Bar in live data with the valve disconnected.
The valve must be sticking or blocked. The valve can be removed for replacement or inspection.
In this case a large amount of metal swarf was found inside the fine filter that is fitted, this must be preventing the fuel escaping. We cleaned the filter and replaced the valve. The swarf must be coming from the fuel system, and without a comprehensive repair history, we could not be certain the fault had been repaired or was the component still breaking down.
Due to the high costs involved it was decided that the best way forward was to return the vehicle to the customer. The vehicle has been driven for 3-5 thousand miles without issue.
