VW Van vibes
A VW T5 van with some vibration issues was taken on a long trip to get it back to Lancashire so Frank could take a look at it. Was it worthwhile? What do you think?
By Frank Massey |
Published: 06 April, 2020
While preparing this month’s topic, it occurred to me that a short explanation of the process behind the scenes would be helpful. All the topics I have presented here over the years have been prepared from real issues we have been presented with in our workshop. This guarantees authenticity and technical credibility.
The topic for this month is focused on a VW T5 van suffering severe vibration. I will begin by explaining that no repair authority was given at the conclusion of the diagnosis. The decision was based on a value versus repair cost and not through any disagreement. All cost was paid without objection.
The owner is a customer known to us. He often uses the vehicle for long journeys over extended distances between Lancashire and Cornwall. It was while down in Cornwall that the problem of vibration that brought the vehicle back to us began. The vibration was present with the engine running. In addition, it displayed a change in tone and reduction of intensity when full steering lock was applied.
While in Cornwall, we understand that a new alternator and power steering pump was fitted with no effect or reduction of vibration. Following this work taking place, with no change to the problem being seen, the decision was made to drive the vehicle to his regular trusted repairers. I.e, us! This was brave to say the least, and potentially teeth-rattling for the duration of the drive back up to Preston.
In an odd sort of way, the diagnostic process had already begun as the van did in fact reach us, and did not display any additional problems. Power delivery was reported as normal, suggesting that the primary rotation engine components were working normally. Our initial checks were visual with a full serial evaluation showing no reported errors. The problem appears to be mechanical in nature with no collateral influence.
Before discussing the laws of physics when applied to a motor vehicle, why don’t we explain exactly what vibration is, and how it can escalate end cost if not accurately diagnosed.
Vibration is mass energy from a source, taken through the transfer path to a respondent. Not only is this wasted energy that could be converted into traction, it will also lead to premature component failure if left to continue.
Vibration is experienced in three ways; feel, sound and sight. How we experience it depends on the amplitude and frequency. High mass energy occurs at lower frequencies and is more likely felt and heard. Low mass energy occurs at higher frequency ranges often felt and seen.
Traditionally vibration has been diagnosed based on opinion rather than evidence. So, what’s the problem? Finish reading this article then you will understand the problem and risks. Vibration can also be affected by the transfer path and respondent. For example, a high mass vibration may be amplified by a light body panel or vehicle trim.
NVH
To succeed with NVH you must first forget you are working on a specific system and focus on frequency and amplitude. The motor vehicle is a series of mechanical systems in permanent conflict, a little like a modern marriage!
There are multiple components with mass differential (weight), vector conflict (direction), frequency (speed), and amplitude (volume). The Pico NVH kit uses a three-dimensional accelerometer and microphone, or multiples of each. They convert mass into a pictorial graph, bar chart or three-dimensional topography.
The primary requirements are engine speed via the serial port or optical input, transmission ratio data, and tyre size. With this information, the software will distinguish the area of responsibility along with any collateral transfer path and respondent frequencies. Further discovery is possible by entering individual component rotation ratio, for example power steering pump.
Physics lecture over. On to the T5. We did not need to enter tyre size as the vibration was present simply with the engine running. Crankshaft data came via a Mongoose serial interface with the accelerometer mounted directly on the engine.
Referring to fig.1, the left scaling is mass in milli gravity, the base scaling is frequency response.
E1 represents the crankshaft, E2 represents combustion mass. The cursors represent the number and ratio of events corresponding to E1.You can easily see that the vibration in the centre of the graph has no relationship with the crankshaft frequency or combustion events. That the frequency is higher (lighter mass) than E1/E2. Now we need to evaluate the engine mechanical ancillaries. These are driven by a complex gear train at the rear of the engine.
Looking at fig.2, note that the tension sprocket housing a counter rotation spring arrangement. Now for the maths based on the gear train ratios; The alternator ratio 2.62:1, power steering/air conditioning 1.59:1.
Now examine fig.3 to see the revised image. E1 frequency 13hz x 2.62= 34 hz, so vibration is caused by the alternator mechanical drive system. There is a drive shaft and cush drive coupling which transfers drive to the alternator. The secondary event at 66.6hz is a respondent event, probably body vibration.
Conclusion
Now for the knockout punch! The tension gear sprocket is not available separately; in fact, you must buy the complete short engine. I seem to recall David saying it is £5,500, notwithstanding the labour cost to build and fit into the chassis. Hence uneconomic repair diagnosed without any intrusion whatsoever. Diagnostic time 0.5 hours plus the ubiquitous coffee break.
Convinced? Join our NVH training programme. Or pay me and I will come and listen to your noises.
- The happy camper
It’s only when you visit the past that you realise how far the journey to the present has taken us. Some time ago Martin, a very good friend of mine from Londonderry, sent over a set of very early EVL Bosch injectors.
This injector pattern started life around the late 1960s and ran through to the mid 1980s and was used by Ferrari, Volvo, Opel, and many others. The set supplied to me came out of a VW camper van, and like many from this era were badly rusting and contaminated from in-tank corrosion. At the time fuel lines and tanks were made from untreated mild steel, and filtration did not meet current standards of 5 microns, or 2 microns with the latest HDEV 6 injectors. The biggest single cause of wear and failure was water ingress in gasoline due to condensation and external ingress.
The injectors were in a bad condition, sticking, blocked, and dribbling. I started the cleaning process with an external pre-clean ultrasonic tank before risking contamination in our ASNU bench. Several cleaning sessions later, with a varying degree of improvement, we arrived at a fully serviceable set.
I posted them back assuming it would be the last of my involvement. I should have known better. Martin and Matthew at Conlon motors have been involved with our training programme over many years. I travel over there several times a year for onsite training, and you have guessed it, waiting for me on my last visit was the camper van.
It was running extremely rich, blowing blue smoke. You could taste the emissions. If you have ever followed a vintage car you will know what I mean. This is where a trip down memory lane started. I have not worked on this system for many years. In fact it was on systems like this that our current-day diagnostic processes were developed.
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- Logic, process and intuitive thinking
Every so often a challenge comes along that demands, knowledge, skill, and a high degree of logic for the approach. But first, a little reflection over the last few months, and a trend I have noticed, namely that I do not quite understand why we are undertaking such major repairs on relatively recent vehicles.
What could be causing this? One possible reason could be a combination of complacency, lack of affordable maintenance funds on the part of the owner, or a substandard maintenance history. At ADS we have probably replaced six or more power plants with costs reaching very high thousands.
Are they owners purchasing vehicles they cannot afford to maintain properly, thereby leading to catastrophic mechanical failures? Or are these unlucky drivers simply not receiving the right kind of professional advice from the independent sector? If the latter is true, then we all need to take on the responsibility before we are branded bandits and opportunists cashing in on vulnerable owners. I’m not suggesting that a garage should become a charitable institution, but surely there is a profitable middle ground?
Distinct priorities
Back to the point at hand. This month’s problem could have developed into a major diagnostic failure had it not been for ADS’ Dave Gore, our diagnostic lead technician, a.k.a Diagnostic David. I would also like to thank James Dillon for th week’s boot camp training. Peter, our workshop technician, returned enthused and confident in his new skills.
The vehicle under consideration is a VW Golf 2.0 diesel EDC 17 common-rail with SCR after-treatment, which includes dual EGR.
I am going to begin with an overview of the potential complexity and problematic SCR additive system. Manufacturers are wrestling with a greasy pig in their attempts to clean up diesel combustion. I accept there has been big improvement, but it falls well short of the ideal and has without doubt introduced more problems than improvements.
The dual EGR system has two distinct priorities from cold. The hot exhaust gas is diverted by the high pressure EGR valve directly into the inlet manifold. The purpose is to rapidly heat the catalyst and DPF.
The low pressure EGR acts in a traditional manner with its priority to reduce combustion temperatures therefore reducing NOx. So far two valves, and the third valve is an exhaust brake. This throttle is fitted after the DPF/catalyst in the exhaust downstream, and is partially closed to raise the exhaust gas pressure during SCR additive treatment causing the gases to make a second pass through a water cooled egr cooler and DPF/CAT. This ensures the urea is fully saturated within the substrate reducing NOx.
The intake module, as it called with VAG vehicles, also has a water-cooled intake air cooler.
Discreet and regular
Our Golf was subject to a discreet and regular loss of coolant. No external leaks were detectable, except what appeared to be a leaking pressure cap. The car had no obvious issues, was smooth running with exhaust emissions that appeared normal.
Rather than just dive in and confirm the problem, I think it’s much more important to explain the tool options and diagnostic process. I have often used this phrase on my training courses many times; “The process is more important than the repair.” In other words, knowing how is a greater priority.
Water loss possibilities? External leaks or internal leaks? Given the current SCR additive system, engine layout, and lack of accessibility the process and tools will determine success or failure.
Cylinder assessment
Given that the pressure cap was showing deposits on the header tank spill, although not consistently, suspicion lay with compression entering the coolant jacket. Applying the chemical combustion leak detector on the expansion tank showed no evidence of combustion gases within the coolant.
So, a new cap was fitted with no effect. The next option was to conduct a live in-cylinder compression test. The problem with diesel vehicles is the omission of pumping losses (the resistance to engine Volumetric efficiency), so it is imperative to introduce an intake restriction this allows for a drop of in cylinder pressure during the intake stroke.
Most of you by now will accept my assertion that vacuum does not exist where as a pressure differential is much more accurate for in cylinder assessment. By restricting the intake, a greater pressure differential is present during the pistons descent, therefore confirming good sealing properties of valves, piston rings and hopefully cylinder head gasket.
Driving conditions
With faults still not found thus far, David’s next move, was in my opinion, a textbook in logic process and intuitive thinking.
The clue lay in the fact that coolant loss only seems to happen during driving conditions.
David attached the Pico WPS to both the charge pressure circuit and coolant jacket. When driving the vehicle on load, both pressure sensors indicated an increase in pressure during turbo assistance. In simple terms, the rise in pressure was symmetrical.
Convinced the head gasket was not at fault, David assessed the problem to be the inlet cooler.
Removing the cooler and conducting a pressure test confirmed an internal leak. So, in conclusion based not on opinion but actual test data evidence, David assessed the problem as a positive pressure differential during turbo boost, which was pressurising the coolant jacket, and pushing coolant out of the filler cap.
This is the reason why I always discuss pressure differential rather than suction, compression, or vacuum. Why? Pressure differential produces flow, from high to low.
In conclusion, avoiding the catastrophic error of a wrongly diagnosed cylinder head gasket, a new intake cooler
was fitted.
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