Performance related

Frank Massey assesses poor performance issues

Published:  08 January, 2017

Recently, a VW Golf R was brought into our workshop, complaining of a poor idle and a reduction in throttle response. Maybe I should say it was the customer that was complaining!

The Golf 888 engines employ the MQB control platform, it's quite an advanced drive train, so caution is the word of choice when dealing with them. The serial data is epic those of you with VCDS or OE platforms will testify, so here is where you start!

There was evidence supporting a problem with mechanical relationship between crankshaft and camshafts, coupled with actual and specified deviation map sensor values, and I do like this one, number of misfire events per 1000rpm.

The problem with extensive data is clarity and purpose. It's a bit like the lottery -  you only need six numbers, or I should say the right six. The data may be tempting and should not be ignored, so how should we proceed? Here are my recommendations.

First, I would like to explore the 888-power plant. To give it full justice, I think it would need around 20,000 words, more than I have available to me, so here is the abbreviated version:

Four cylinder, two litres 290bhp, twin camshafts with Audi valve lift ((ex) variable timing on both camshafts, dual injection. Manifold port injection for mid-range driving and direct injection for high load demand. couple this with fuelling delivery that offers homogenous or stratified delivery with split and single delivery events.

What we have here is cutting edge high performance from a mass-produced engine. I own a Seat Cupra with REVO stage 1 software delivering 380bhp. A traffic officer recently pulled me over and asked if I hadn't seen the 30mph sign when entering the village, to which I replied: 'what village?!'

Back to the problem, how many of you remove the spark plugs and examine them? Did you know they have a service life of 6 years? Where next, the fuel filter? well there isn't one as such. So we must proceed with caution; the word misfire is misleading. Combustion anomalies is my expression for what is in effect incomplete combustion.

The causes fall into three simple categories

The skill sets here are in eliminating misleading evidence and employing accurate non-intrusive, test techniques.

Eliminating ignition, is a task for the Pico scope, four critical measurements are required to confirm the correct electrical energy delivery: burn time, primary current profile, coil ringing, firing line voltage.

Eliminating fuelling, is a joint task of careful serial evaluation, which is extensive, and thorough. Testing injector inductance, flow and spray pattern using our ASNU test bench. However, this task was postponed due to the labour time in removing the manifold in favour of mechanical evaluation.

The normal preliminary mechanical tests focus on compression evaluation or cylinder leakage testing. Nothing wrong here except there is a much quicker and more accurate method, bringing us to the point of this topic.

The PICO pressure transducer was coupled with a standard compression gauge hose with the one-way valve removed. Select range 1 option 2, removing one spark plug only. We intend to run the engine plotting the total cylinder pressure across a range of engine speeds. To make full sense of the Pico image provided I strongly suggest forgetting atmospheric pressure as a reference value and consider the total pressure (ABSOLUTE) value.

I have gated the waveform with cursors which divide pressure against angular engine position.  Compression events are obvious, less obvious is the relationship of the remaining Otto cycle. I deliberately intend to leave the evaluation to you! However, think very carefully about what direction the piston is travelling and what position the valves should be in. boyles law principle lays down how gasses under pressure behave. Enough clues, enjoy the challenge.

It's not a tease but vital that the principles of the 4stroke cycle is fully understood in real time. Consigning the compression gauge to the stone age, I hope.

The answer to our Golf problem was due to the timing chain jumping three teeth. the front cover is relatively easily removed, and with new tensioners, restored normal performance. However, there is a lot more to this story

The timing requires serial adaption following repair, this is supported with data blocks 06726-36. the oil supply system has a variable displacement oil pump mapped against engine load, with the lower pressure around 1.8 bar (brown switch). It is essential the correct specification oil and filter be fitted. we (ADS) do not carry out extended interval servicing and use only OE parts. We see so much premature system failure due to one simple problem: Incorrect servicing.

Thanks for sharing this experience, if your seeking training at our preston workshop or want me to come to your premises, contact

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