Unusual failures - jerking of the 1.9 TDI engine

Turbo-Tec Research and Development Centre is a specialised laboratory with a professionally equipped service centre, where cases of failures that are difficult to verify and repair are diagnosed. One of these was the VW 1.9 TDI engine, which was experiencing jerking.

Our sales department was contacted by a customer with an order to verify the technical condition of injector pumps used in VW's 1.9 TDI engine. His concern was jerking of the vehicle occurring in the engine speed range of 2,000 to 3,000. At the same time, the customer checked the parameters of the power supply system using his diagnostic computer and diagnosed incorrect values of pump injector corrections on each cylinder.

On the basis of the faults described, the mechanic decided to dismantle the injectors and bring them in for testing. After the test was performed on a test bench dedicated to such pump injectors, under-injected fuel doses were detected in the medium and high load range of the engine. - says Piotr Kozub, R&D employee, who also deals with warranties.

The customer opted for the repair, which was carried out, and the repaired, and re-tested injectors were delivered to the customer after the repair. The customer alleged that after fitting a set of pump injectors to the vehicle, it was found that the situation had not changed, the engine was still jerking and not running normally.

- I contacted the mechanic and suggested some tests to make sure everything else was working properly. At my request, the mechanic checked the pressure values at the pre-pump, the pressure after the tandem pump, he also checked the electrical system, looking for some lost ground, and finally he made sure that the compression pressure in each cylinder was correct. To be on the safe side, using a second vehicle with the same engine, he even swapped the controllers, but all these steps showed no abnormalities and the condition of the vehicle, i.e. the annoying jerking, remained unchanged. - says Piotr Kozub.

- I decided to help the customer personally by examining the vehicle at our service centre. I was convinced that we must have missed something. We accepted the vehicle, took a history from the customer and began to find the cause of the jerking and loss of engine power. After checking the correct installation of the pump injectors in the car's head, which also included an assessment of the sockets themselves and the compression ratio, we did not detect any abnormalities. However, for safety's sake, we fitted the injectors once again, removing and then fitting all of them step by step in accordance with the installation procedure. - explains the Turbo-Tec specialist.

- Dynamic tests on the vehicle began. Analysing the data from the customer, and the tests he had performed, we noted that the fault, unlike the tests, occurred when driving on a loaded engine, and the tests were performed at idle and without load. I recall that the jerking was occurring at speeds in excess of 3000 rpm.

We focused on the tandem pump. During idling and no-load operation, all parameters were normal, but during acceleration the pressure generated by the pump dropped all the way down to the minimum pressure, at the same time the car started to jerk. And this is where the first suspect finally appeared," notes Piotr Kozub, "our attention was focused on the pump operation.

The next step was to check that the correct pressure was reaching the pump from the fuel filter. Again, there was a pressure loss effect under load. Further checking included checking the patency of the lines, filter and basket in the pre-pump in the tank.

Eventually, it became apparent that replacement of the pre-pump in the tank and cleaning of the basket was required. Without giving it much thought, we replaced the pump with a new one and started further tests, first in the service hall and then on the road. The fault has not recurred," says the Turbo-Tec specialist.

Even an engine as familiar as the 1.9 TDI can cause problems. Diagnostics is a complex and complicated process, requiring both knowledge and specialised tools. That is why Turbo-Tec dedicates a Research and Development Centre as an added value for its customers.

- If you find yourself in a hopeless, difficult case that does not give you peace of mind, contact us and we will certainly take care of your case too. - declares Piotr Kozub, employee of the Turbo-Tec Research and Development.

The article appeared on Motofocus.