17 Jul 2024
The voice of the independent garage sector

A vote for independence

By Frank Massey

This repair fell right in the middle of the Scottish vote for independence so we were considering the possibility of an export licence with the distance and borders involved between the owner’s home near Biggar and our Preston workshop. However, the owner specialised in transporting vehicles across the country and offered to drive the Citroen Relay down to Preston.

The Relay had some interesting problems – with a second-hand engine, a replacement gearbox and a new EGR valve for starters but I am sure there was more to consider. The vehicle didn’t quite make the journey unaided, a bit like the vote for independence I guess. Upon arrival, a quick serial scan reported faults with number one injector and turbo boost negative boost deviation.

The evidence so far suggested a loss of boost to be a simple system leak and until repaired, no further tests were possible. The badly misfiring engine could be due to several causes, including a fuelling error, a mechanical error or an internal or ancillary component such as the EGR valve. The symptoms and a hard DTC error relating to number one injector gave us a sensible place to start.

All the injectors were removed for a comprehensive bench test and this revealed number one injector was electrically faulty and one injector was hydraulically faulty. The remaining two injectors passed all bench tests and were refitted. Two genuine new injectors were also fitted after re-cutting the compression seats.

Having cleared the DTCs, our next task was to log key data relating to turbo boost, EGR feedback and injector smooth running balance. All of these proved normal, in fact, the vehicle performance was remarkable. A week after returning the vehicle and following several hundred miles of use, the customer complained of diesel knock and a flat spot but only when cold. We discussed the options and symptoms, agreeing to replace the two remaining injectors. I carried this work out at his home and must agree that the diesel combustion noise from cold was reduced and a test drive also confirmed no flat spot.

Some three weeks later, we had yet another call from the owner, describing what sounded like serious problems – a lumpy engine, smoking and lack of power. Confident of my work so far, I suggested the sensible option of transporting it back to our workshop. Upon receipt, the only problem we discovered was a slight air leak from the plastic filter housing. As this was a suction system, a lack of fuel and cavitation would cause severe running problems. A complete new housing was fitted and fully tested with our ADS low pressure gauge. This confirmed a perfect seal and the status of the high pressure pumps ability to create a pressure differential across the filter housing.

To be absolutely certain, we decided to keep the vehicle over an extended test drive. After several days and some 150 miles of faultless performance, the exact symptoms described by the owner occurred. The only clue was excessive diesel knock and smoking. With no additional DTCs, we believed it had to be a fuelling combustion problem.

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