Having a good process

Frank looks at a number of issues which affect everyone in the industry

Published:  22 October, 2014

By Frank Massey

I promised the guys on a recent weekend training course to conclude the tests we carried out with a repair solution. For the benefit of everyone else, let's start at the beginning. The Polo 1.4 GTI DSG employs a recent variant of the direct petrol injection system, MED17.9.

The initial first look confirmed no DTCs but the vehicle did suffer an extended cranking prior to starting. Once started, it ran smoothly. Some ten years ago I developed a process of testing hydraulic high pressure pumps using analysis from the pressure sensor profile. This was initially used on common rail and later adapted for petrol high pressure systems. Having no test data on this system variant it presented a perfect challenge to the diagnostic process.

Direct petrol injection is very similar to common rail diesel control and the initial test sequence began by looking at the key critical requirements, firstly the ignition drivers, secondly injector drivers and third, rail pressure. The result of this composite observation, and we can now reveal our involvement in developing the new 'Rainbow' Pico scope, confirmed an unusually slow pressure build-up.

The next stage in the process involves intrusive tests. This part of our past development programme was designing a low pressure test gauge. The requirement was to monitor suction or positive pressure priming systems together with flow and the ability to conduct pump proof testing under real load conditions. Applying this test confirmed excellent low pressure priming with 6 bar available to maintain high pressure pump pressure.

pressure pump pressure. The most interesting aspect of our initial observations, unique so far for petrol systems, was that until a certain pressure was reached, no triggering of fuel or spark took place. We also noted that no driver outputs were present at the high pressure control valve, so no current was present either. This further confirmed our training group's findings that the valve is actually a volume control device. Proving this theory also follows our common rail pump proof process; removing current at 2,000 rpm immediately caused the pump to run at full pressure 115 bar.

The decision? You need a new pump mate, with just one caveat - check the camshaft drive lobes and follower. Other non-relevant issues found included a reduced burn-time on coil three and no current transition across the wideband sensor.

Replacing the pump reduced the rise time to 630 milliseconds. It was also noted via TPS that the pump had undergone several part number updates.

This brings me to our involvement in the OESAA initiative and the hands-on technical conference this November. My workshop is seeing an increase in repair reworks. Each case without exception has been due to the owner opting for price not cost! Reducing the cost of a repair is easy; you cut corners in the process and use substandard parts. As a footnote to parts supply and the independent trade, we recently received a LuK OE dual mass flywheel, nothing wrong in that, except it had been pre-fitted. The well-known supplier wanted to return it as a warranty claim!

Replaced:?A new pump brought the figures back to the expected times

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