Par for the course: VW Golf R mystery, part one

A lack of power on hard-driven but well-cared for track day Golf R causes some head-scratching for Frank. Can he get to the bottom of it?

By Frank Massey |

Published:  07 January, 2020

It’s not often you get two bites of the same cherry, but in my case, it happened just one week apart. The story begins many months ago with one of our regular customers. The customer in question is a real enthusiast and a keen track day driver. His car of choice is a Volkswagen Golf R.

Having modified the car over several months, we now have a 500 BHP-plus Golf. It has KW variant 3 suspension with Eibach roll bars, a floating brake disc upgrade, and lightened shell, roll cage etc. It also employs a MBQ electronics platform. I could continue but I think you get the idea.  

It’s fully fettled, but even with the best kit and care, you are bound to have something go wrong eventually. Can you guess what happened? That’s right, a problem occurred!

Lack of power delivery
During a track session the car suffered a lack of power delivery, with no abnormal symptoms, misfire, oil consumption noise or vibration.

The Initial investigation began with a serial scan with no DTS present. It is at this point a diagnostic strategy should be put in place. The phrase ‘first look’ involves the principle of gathering as much information without intrusion as possible.
Where to start and which option to take depends very much on the symptoms. In my case the initial tests were conducted in my absence.

A full load data log indicated a specified and request turbo boost pressure of 2.8 bar absolute, with an actual value of 2.3 bar indicated. These values will no doubt illustrate the level of modifications to the power train. The car still delivered a powerful drive experience although the actual power experienced was less than expected.

Well-established test process
This is a common problem and with a well-established test process. The charge pressure circuit was pressure tested without any external leaks. Because the en888 engine does not employ an EGR valve, we did not believe that the cause could be the result of internal leaks. Our first idea actually pointed towards the hybrid turbo, which we initially suspected as the prime cause of the ailment.
I was asked to call into the workshop to review the results so far. I suggested a NVH in cylinder profile be conducted. This engine employs variable camshaft timing on both cams with lift extension on the exhaust cam. With this in mind, I was especially interested to examine the valve piston relationship and the valve pocket profiles.

The results immediately confirmed significant errors to the intake and exhaust valve pockets with excessive exhaust pressure. This engine variant should have little or no pressure above 1 atmosphere, or 1,000mb. during the exhaust stroke, my test results confirmed over 1,700mb absolute. Valve pockets represent the pressure differential across the four-stroke cycle and accurately represent the mechanical efficiency of the Otto Cycle. This is often referred to as pumping losses. So, we have a restriction in the exhaust stream, turbo, catalyst or exhaust system? Removing the flange pre-catalyst enabled examination of the turbo hot side and catalyst intake.

Reduction of boost pressure
The catalyst substrate was detached and turned through 90 degrees. In this way, we discovered the symptoms. A restricted exhaust was reducing both air intake volume, therefore load calculation, and turbine volume. The result was a reduction of boost pressure.
Next, we needed to discover the cause. Excessive heat and expansion, followed by the catalyst detachment. This was interesting, not least because a recent upgrade to the fuel priming system resulted in the fitting of an upgrade in tank pump. The result of which only became known after a track session where a drop-in top-end power resulted in a DTC rail pressure negative deviation.

The pump module, a specific upgrade from a respected independent VAG tuning specialist, had been supplied with the incorrect o ring. This resulted in a slight drop in both flow and pressure together with cavitation causing a lean mixture ratio at extreme load.
So now we have the complete trio, fault, symptoms, and cause.

Happily ever after?
That is not the end of the story however, as this particular VW Golf R returned just a week later. The good news was the owner’s report of exceptional performance. However, the bad news was that with the returned power came horrific vibration.
That’s a story for another day though.

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