Rocker on Tommy?
Frank tiptoes through Audi variable valve lift, focusing on operation and points towards diagnosis and how to make repairs
By Frank Massey |
Published: 24 January, 2023
Vehicle diagnosis is not dissimilar to navigating a minefield; Tread carefully. How’s that for an opening line? Not exactly an encouraging start I know, but bear with me. Within this topic I am going to explain Audi variable valve lift operation, design, servicing, and diagnosis. In order to underscore the risks – I did just say it’s a minefield – I have an actual fault from our workshop.
Principles of operation are remarkably similar across all engine groups. They are some differences though, operating on either inlet, exhaust notwithstanding, or cylinder select variants. The camshaft responsible for shift and lift control has a spline. On this is a sleeve containing the lobes for operating two valves independently, which slide laterally. Two helical grooves provide for the actuator’s engagement and disengagement. The lateral movement of approximately 7mm is locked by a spring-loaded ident ball, like that controlling gearbox selection rods. Please refer to Fig.1, which shows a variable lift control sleeve.
Different engine types vary in the approach, but this should broadly explain how the system works. Inlet valve operation is asymmetrical, i.e., each pair of valves operating from a common sleeve share different lift and closure profiles, but they open together. The closure event is offset however. This improves cylinder charge and creates a tumbling motion with the fresh air intake. Intake swirl flaps are no longer required complimented by Audi TFSI piston crown profile.
Due to physical limitations, the valve rocker arms on the variable lift camshaft are required to be narrower than their fixed-opening counterparts. This has been complemented by larger roller bearings. The lift control actuator is not a simple solenoid, controlled by the engine PCM. A permanent power supply is switched to ground via PCM command. This is achieved by a saturated control pulse, identical to early generation 15ohm injectors. The actuator pin is extended by a 3amp current flow with 100 G acceleration, requiring a permanent magnet and percussion damper to prevent the pin bouncing out of the helical groove. The back EMF pulse is used by the PCM to confirm actuation.
The actuation pin return is provided by the helix ramp, which also generates a small voltage spike which the pcm uses to confirm end of lift operation. If high lift operation fails, the PCM will limit the RPM to 4,000, with all cylinders in low lift with reduced power output. If high lift return to low lift fails, the PCM will hold all cylinders in high lift with full power and RPM, however idle will be less smooth.
I mentioned alternative variants; Take as an example the 2-litre 888 engine. Here, the exhaust valves share lift modification and cylinder select variants, whereby the PCM selects a zero-lift lobe preventing cylinder charge. This provides a pneumatic damping for the reduction in cylinder operation.
Example
The vehicle in our workshop, an Audi SQ5, was presented with a complaint of intermittent rough running. I deliberately avoided the phrase misfire as incomplete combustion may be caused by ignition, fuelling or mechanical faults. Tiptoeing through the minefield, David Gore our diagnostic tech at ADS initially appeared to rule out all three possibilities. Please refer to Fig.2, which shows the minefield…sorry…engine in question.
Via a scan using his Pico scope no ignition anomalies were found. This included monitoring spark line profile and primary current ramping profile. Fuelling errors were carefully ruled out with observation of fuel trim and oxygen sensor data. Broad band sensors are highly effective at responding to excess oxygen content in the exhaust stream. While fuel trim may mask subtle fuelling errors, the rear catalyst zirconia sensor will always display an incorrect voltage. Nominal voltage from a stable load condition should be 0.7volts. The fuel injectors had not been removed at this point due to the balance of fault probability against cost. Do not let this consideration deviate your need to conduct further potentially costly testing though. David also conducted cranking current analysis, confirming uniform current draw on compression across all cylinders.
This is a simple, accurate, means of comparing the physical load expressed in amps in overcoming the work done during the compression stroke. Initial results normally conducted over 10-15 seconds showed no deviations across all cylinders. In a throwback to the old engine tuner days, cranking tests were extended to 30 seconds at which point he discovered a single cylinder discrepancy with current draw. This must be a mechanical consideration only. I was not excluding an injector fuel delivery problem at this time, which could cause bore wash, affecting compression. Please refer to Fig.3, a Pico image showing compression loss.
Synchronizing the event with number 1 ignition coil 5-volt PCM control signal, he quickly established the faulty cylinder. Upon dismantling the engine top end, a faulty rocker bearing was discovered, the effect of which allowed the rocker to hold the valve slightly open. Please refer to Fig.4, which shows a faulty rocker.
Assessment
Further investigation via ETCAS confirmed a modified version of the rocker was available. The vehicle is currently awaiting the necessary modified parts. This brings me back to my earlier comment about servicing requirements. As specialists in Audi and VAG in general, we see extensive premature engine mechanical failures. In my assessment, this is due to long-life servicing strategies, often recommended by dealerships or adopted by owners as a cost-saving measure, with extended intervals between services. This is generally a bad idea.
We have several clients operating similar engine variants with trouble-free mileage approaching the 200,000 mark. This we believe is due entirely to oil replacement intervals not exceeding 10,000 miles or 12 months.
- New SUN 4000kg 4-Post Service Lift
Snap-on has unveiled the SUN SVL-40S 4-Post Service Lift. The 4-poster is an electro-hydraulic service lift with a rated lifting capacity of 4,000kg and is being made available in a surface mount configuration with a drive-on, reverse-off arrangement. It can lift within a range of 180mm to 1,830mm, and includes mechanical ladder locks on all posts, along with a buzzer on the final stage of descent. The main lifting platforms measures 4,888mm by 630mm, with a 915mm opening. The lift can take on vehicles up to and including LCVs.
https://bit.ly/SUN-SVL-40S-Service-Lift
- Hybrid Working: Do people still need to own cars?
In less than three years, workforces all over the UK have become accustomed to a hybrid working system of both in office and from home. Going into 2020, the number of people who had worked a single day from home was only around 12%. This rose to almost half of employees during June 2020 and while there was a decrease after world events began calming down, the statistics were still higher than pre-2020. September 2022 saw 22% of employees state they partly work from home regularly.
Companies are still looking to embrace hybrid working and with more people working from home, it means less time commuting to the office. Adding this up to the problems associated with driving, such as rising petrol and diesel prices and delivery delays for new cars, many drivers won’t need or want to use their cars as much. There are plenty of options available if you are hoping to reduce your driving. In this article, we will take you through some of the best solutions to get around.
Bike and scooter hire
Many cities in the UK have started introducing new methods of getting around with bikes and scooters that you can pick up and get going on. Statistics have shown that many trips in the UK tend to be short, with 24% of trips being less than a mile and 68% of trips being less than five miles.
Micromobility is the idea of using smaller, lightweight vehicles for travel like bikes and scooters, and is a fantastic solution for shorter journeys. Especially if you live quite close to your place of work, shorter commutes will benefit greatly from embracing these options. Not only is it more cost-effective, but it will also mean a reduction in emissions compared to what is produced when driving, thanks to the lack of fuel required to power them. Bikes and electric scooters are common options, and there are even electric bikes in some areas. Accessibility is made easy thanks to most providers having an app that you can create an account for and rent one of the vehicles for the time or distance you need it. Once finished, you can find a designated point to leave the vehicle using the app, while some allow you to leave it parked in a safe location
Car sharing
Many companies are now introducing car-sharing schemes that act like a combination of car rental and micromobility. Apps are available for these services, so you can see the GPS location of a car on the system. Using a booking system or calling direct, you book and then use a smartcard or your phone for contactless to unlock the car without the need for keys.
This is a great option for drivers who may need to make the occasional (and sometimes unavoidable) longer trip but don’t want the hassle of owning a personal car. Not having to worry about cleaning or refuelling the car, as well as long-term concerns like servicing and insuring the vehicle, means you can choose when to drive to suit your needs. Once you’re done, simply park in a designated spot for it to be used by another member of the service.
Public transport discounts
Each city and region in the UK has their own public transport systems. Some examples are regional rail systems like the Tube in London, the Tram in Manchester and the Metro in Newcastle and Gateshead. Buses are also present up and down the UK, all running until the late evening hours.
While using public transport consistently can mean you build up costs over time, there are ways you can bring these overall costs down. This can include investing a bit more at the start of the month for a season ticket that will cover your travel for the rest of that month. Similarly, you can get a bus or metro pass that you can top up with credit so you can simply swipe or tap to ride. The drive for people to use public transport more regularly has inspired government incentives to make travel more affordable. A great example is the Get Around scheme that has been introduced between January and March 2023, which offers single cap tickets of £2 for the full three months.
Owning a car can be incredibly useful, but the rising costs could be enough to drive motorists away from sole ownership. If you would prefer to own your own car and live close to someone else who can drive, you could look into joint insurance that allows you both to drive the vehicle. That way, you could spread the costs evenly across both drivers.
www.co-wheels.org.uk
- A month in the life of a vehicle technician
In this month’s article, I have chosen a very diverse collection of challenges presented to me, with a mixture of diagnostic problems and mechanical engineering issues. I am going to focus on the engineering issues later as I think they expose typical shortcomings seen in many garages, specifically with experience and engineering assets.
My first story should shame us all with regards to garage ethics. I was asked to check an engine MIL light on a hybrid Honda. The extracted code suggested a bank 1 sensor 2 heater circuit error. I opted to raise the vehicle and examine and remove the offending sensor. Once raised it was clear the catalyst had been replaced with a straight length of pipe, removing the post cat sensor and tucking the open socket into a chassis lightning hole. Please refer to Fig.1.
When checking the vehicle records, I noted the catalyst had been removed and discarded with the sensor during a previous MOT test. As hybrid vehicles do not require an emissions test, a MOT pass certificate was able to be issued. I am not clear what implications the MIL lamp status would present during the test. The notes also indicated the customer could not afford the cost of a replacement catalyst. Here is my take on this; We are not here to offer a financial lifeboat to vehicle owners. We are here to offer a professional, durable, and efficient repair service, at a cost. We should however also offer accurate technical advice as to cost value ratio.
Avenue of rectification
BMWs - I love them! Well, not really. A 320d that came into us failed its MOT for a nearside brake light failure. Initial examination exposed water ingress in the light cluster socket. Please refer to Fig.2. A replacement housing and socket with new pins duly arrived and was fitted. All lights except the brake light worked. Serial interrogation showed the maximum number of ignition cycles, which is 50 in case you were wondering, had been exceeded. Therefore, the voltage supply to the stop lamp is permanently interrupted. Please refer to Fig.3, showing BMW serial data.
Initial research suggested a new footwell module was required. However, further research uncovered that it was possible to access the lines of code and reset the ignition cycle count registry. This demonstration was not using an OEM service tool. As I was on holiday I am not sure what further steps were taken to explore this avenue of rectification. I do know we did replace the module and perform a repair. There are so many fuse and relay panels on BMWs, so why not have one for lights? Answer me that, Munich.
Simple things
Next, a Land Rover Discovery - I love these as well! This one came as a non-run vehicle. “Why?” I hear you say. Well, apparently, a low SCR additive warning had surpassed the final warning status. Serial data appeared to indicate the additive tank was overfilled. The filler is under the bonnet, with the tank located at the nearside rear, adjacent to the wheel arch. Once the hard-shell cover is removed, a drain gland allows easy draining. Not so fast, three simple things to do. First, smell it; It should be odourless, with a SG of 32.5%. Next, check the quantity. Finally discard it and refill with new urea. As I recall, the capacity is 14.5 litres. Using our serial tool reset, all the adaptive values enabled the engine to run. However, several adaptive values could not be accessed due to the following DTCs:
- A month in the life of a vehicle technician
Part One
- Third of drivers would sell car due to £500 cost of living surge
A £500 increase in the cost of living for 34% of drivers would force them to sell their car, a recent survey has found, with a further 29% saying just a £250 rise would be enough to see them let their vehicle go.
