Inject some knowledge

Frank Massey examines the changing role of fuel injectors, and the problems you can come up against when dealing with these components

By Frank Massey | Published:  17 September, 2018

At the heart of fuel delivery is the injector. If there is a single focus point that has helped reduce emissions and boost performance it’s the injector. Despite this, we don’t pay it enough attention, and I include myself in this critique. Let me qualify this by asking a rhetorical question; How many of you have injector bench test capability?

I do, but freely admit to not giving it a more prominent position in fault diagnosis. I am going to expand later just how intrusive testing should be conducted. To begin, a short trip down memory lane won’t do any harm in understanding basic problems.
    
Injector problems started in earnest when lead was removed from gasoline. The Nissan 1.8 turbo and Austin Montego 2.0efi were two of the most problematic examples. Both used 15ohm single event saturated triggering with approximately 1-amp peak current. This was back in the days when we were not measuring current nor did we have an injector bench.
All the diagnostic evidence came from the 4-gas analyser. CO and O2 should balance at approximately  0.5%, as this will achieve a near perfect lambda 1 ratio, 50-100, CO2 at its highest at around 17-18%.
    
A lot has happened since then. The key to ideal fuelling is in reducing the lag or dead time in injector response to PCM control. As engine power increased and turbos became almost mandatory, more fuel was required. To achieve these aims, opening times were increased to a point where they were in danger of colliding at high engine RPM. We are still talking port injection here, fuel pressures crept up to four-bar and high flow injectors started to be introduced.

Current ramping also changed to peak and hold with peak values of around 4-amps. For the time being things stabilised, with little or no obvious common injector problems. The next challenge manufacturers faced was to reduce the internal mass of the injector components. In plain English they got smaller, lighter, less robust, and with lead free legislation less reliable. Remember Fiat iaw injectors?

Precise control
As EU emission rules became more stringent, the need for even more precise control was inevitable, and along came direct high-pressure injection. Lets explore the variables of fuel transportation, variable delivery pressure 50-200bar, multiple injector strikes and adjustable delivery timing. Peak current now reached 10-amps and pwm switching became commonplace.
We now have gasoline injection that more  closely resembles diesel injection protocols. They also bring similar problems. Fuel is no longer delivered through the inlet port, leading to a build up of carbon behind the valves. This effect, the critical swirl in the cylinder, is essential for complete combustion. Filtration and fuel quality are now major considerations for reliability.

Hostile environments and anomolies
Injectors are now mounted in a more hostile environment, more pressure, more heat, more tip carbon. So, the need for testing and cleaning has come full circle from the lead-free era. A major problem here is the stress caused to the injector body by techs not using the correct removal tool.

Remember the comments on lighter internal mass; This means than bending stresses during removal leads to intermittent combustion anomalies. I do love that word, it more accurately describes incomplete combustion, often without any credible serial fault data.

New fault phenomena
Now let’s notch it up a bit and introduce some new fault phenomena. The internals are so light they can suffer mechanical failure, and the closure spring can break. The internal filter basket has been moved to a more central position, resulting in inaccessibility for replacement.

The use of fuel additives, something I used to support, is now dissolving the nylon baskets.
Just when you think you have a grasp on current problems along comes the new kid on the block, compression seal failure causing injector malfunction due to thermal intrusion. This is a major problem with Porsche, leading to engine failure because of localised bore wash.    

Onto bench testing then. The ASNU bench provides for a range of test programmes, open period, frequency, and open pintle flow evaluation. It also provides critical inductance values. This represents the net energy value of the coil energisation, this is also affected by the movement of the pintle through the magnetic field. So how do we apply the true operating environment condition?

The answer is we can’t we have to be a lot more intuitive in our diagnostics when dealing with combustion anomalies. One interesting trait with the Porsche injector problem is the injector frequency changes when it fails. So, we are currently working on vibration analysis across injector types.

The problems don’t get less – just more complicated and more interesting.  

Related Articles

  • Walkabout: The Australian adventure 

    Having just spent three weeks touring New South Wales, while delivering two training events, firstly in Sydney then Canberra I thought it would be interesting to compare how our two different, but also similar markets operate.

    The visit began several months ago with an invitation from a good friend Bob Whyms, Australia’s prominent Porsche specialist in Sydney. The offer comes as part of a training group called Australian Aftermarket Service Dealer Network (AASDN). This is a group of totally independent service and repair independents across the whole of Australia.

     It was formed from disillusioned members from the Bosch Aftermarket Service Dealership Network, or BASDN. Around 70% agreed to form AASDN with the view of promoting mutual support and training across the whole of the continent. Members pay a subscription to a fund that provides venues and trainers across the continent. My understanding is they number about four per season.

    Mutual respect
    It is important to understand the incredible geographical constraints yet obvious bond they share for their independence and mutual respect. If I may reflect on our very own Autoinform event in Harrogate in November, where I am sure all attendees would recognise the same sentiments from the AASDN group.

    I was also privileged to visit several businesses in both Sydney and en-route to Canberra. The BWA Porsche specialist host and first training venue, based in the western suburbs, provides genuine expertise in depth from Bob and now also his son Craig. This ranges from servicing to performance upgrades.

    BWA provide a parts service across Australia importing directly from Germany. They also provide a comprehensive machine shop service, which supports their engine remanufacture and performance business. Bob and I had fun reflecting on Bosch D Jetronic and other early evolutions of fuel injection, grumpy old men and all that!

    I was then treated to a visit to a highly respected Mercedes tuning expert close to the airport. Then finally, a very talented young technician specialising in DPF cleaning. The focus on training included ignition diagnostic technique, common rail and direct gasoline injection.

    It was both a pleasure and privilege to share the enthusiasm from the entire audience, their knowledge and interaction was mutually appreciated.

    In a far too brief visit to Dubbo, my good friend Paul gave me an insight into the more remote reaches of the trade. I was equally impressed with the dedication and superb workshop facilities. I also experienced several near-misses from kangaroos!

    Special mention
    I should give special mention to  my incredible visit to the Bathurst 1000 race. It is an institution among fans and an incredible two-mile hill town circuit, constructed from urban roads. AASDN host a VIP lounge for their members.  Imagine that at Silverstone! It only takes commitment and support with a little cash.

    One week down, heavy rain and in the good company of Alan, a diesel shop owner, we travelled down the coast, whale watching in Huskisson Bay. Then onto Canberra, via AASDN committee member Alan. Despite having just lost his home and all his possessions from a bush fire, Alan remarkably still provided accommodation in his temporary rental home.
    Our hosts in Canberra, Derek and Ros, operate a large high-end diesel specialist shop. The second training event was a mirror image of Sydney, supported by a second incredible array of AASDN members. Incredible not just for their knowledge and confidence but their interaction over the three days.

    The evenings from both events was spent socialising in steak houses chatting over mutual challenges. From my experience the vehicle market share was quite diverse, lots of Asian cars, and a remarkable number of VWs. It was a surprise to learn that that both Ford and Holden have ceased production in Australia due to a lack of competitive pricing. I was told of a delegate who attended the Canberra event who heard of my visit two days before the Friday start, purchased a flight, closed his workshop and travelled from Perth to attend. It is a 3,000km journey. To put that into some local UK context, I once had a conversation with a parts distributor in Kent several years ago, when a training event had to be relocated from Canterbury college to Ashford, 17.5 miles away. He cancelled the whole event without asking the delegates. The reason? He said, “they won’t travel that far.”
    I see little differences between our two cultures. I find the same dedication and passion. Sadly for the UK, they seem to have more of it.




  • Top Technician flashback: Issues of rotation 

    I received a phone call from another garage: “We were wondering if you would be interested in looking at an ABS fault for us?”
        
    The car in question was a 2011 Honda CR-V, which had been taken as a trade in at a local garage. The fault only occurred after around 50-70 miles of driving, at which point the dash lights up with various warning lights. The vehicle had been prepped and sold to its new owner, who was unaware a fault was present.
        
    After only a few days the fault reoccurred and the vehicle returned to the garage. They had scan-checked the vehicle and the fault code ‘14-1- Left Front Wheel Speed Sensor Failure’ was retrieved. On their visual inspection, it was obvious a new ABS sensor had already been fitted to the N/S/F and clearly not fixed the fault. Was this the reason the vehicle had been traded in? They fitted another ABS sensor to the N/S/F and an extended road test was carried out. The fault reoccurred. This is when I received the phone call. The garage now suspected it was a control unit fault. My first job was to carry out a visual inspection for anything that was obviously wrong and had possibly been over looked: correct tyre sizes, tyre pressures, tyre tread and excessive wheel bearing play. All appeared ok. The ABS sensors fitted to this vehicle are termed 'Active' meaning they have integrated electronic and are supplied with a voltage from the ABS control unit to operate. The pulse wheel is integrated into the wheel bearing, which on this vehicle makes it not possible to carry out a visual inspection without stripping the hub.

    Endurance testing
    With the vehicle scan-checked, all codes recorded and cleared, it was time for the road test. Viewing the live data from all the sensors, they were showing the correct wheel speed readings with no error visible on the N/S/F. The road test was always going to be a long one. Fortunately at around 30 miles, the dash lit up with the ABS light and lights for other associated systems; the fault had occurred. On returning to the workshop, the vehicle was re-scanned, fault code 14-4 ­– Left Front Wheel Speed Sensor Failure was again present. Again using the live data the sensor was still showing the wheel speed the same as the other three, so whatever was causing the fault was either occurring intermittently or there was not enough detail in the scan tool live data graph display to see the fault. It was time to test the wiring and the sensor output signal for any clues.
        
    Using the oscilloscope, the voltage supply and the ground wire were tested and were good at the time of test. I connected the test lead to the power supply wire and using the AC voltage set to 1v revealed the sensors square wave signal. Then, rotating the wheel by hand and comparing the sensors output to one of the other ABS Sensors, again all appeared to be ok. A closer look at the signal was required, zooming in on the signal capture to reveal more detail; It became easier to see something was not quite right with the signal generated by the sensor when the wheel was rotated. With the voltage of the signal remaining constant, a good earth wire and the wheel rotated at a constant speed the signal width became smaller, effectively reporting a faster speed at that instant, not consistent with the actual rotational speed of the wheel. It was difficult to see the error, zooming out of the capture to show more time across the screen it could be seen that this appeared in the signal at regular intervals, although not visible all the time because it was such a slight difference. Using the cursors to measure between the irregular output and counting the oscillations, it was clear that it occurred at exactly the same interval every time. It had to be a physical fault on the pulse wheel.
        
    This meant a new wheel bearing was required. The vehicle was returned to the garage as they wanted to complete the repair. A new wheel bearing was fitted and extended road testing confirmed the vehicle was now fixed.




  • Ethanol: flexible friend or biohazard? 

    I am starting to get the impression that governments and vehicle manufacturers are beginning to panic. Let’s begin by accepting that personal transportation vehicles will not be powered by hydrocarbon fuels for much longer. This statement includes hybrid and battery powered vehicles for the same reason. We are being subject to a whole raft of short term impractical solutions, the latest of which and the subject of this topic is bio-ethanol fuels.

    The reason I express this opinion is the true impact on emissions, from production, refinement, and transportation are not included in statistics on their environmental effect. Bio-mass fuel for electricity generation is a perfect example of this. The EU has decreed that emission monitoring of stack emissions need not be published, also excluded are the felling, drying, production and transportation influences.

    Political initiative
    I will begin with the political initiative, a reduction in greenhouse gas emissions, reduction in fossil fuel dependency, alternative fiscal revenue for the farming community, and a reduction in EU farming subsidies. Try not to laugh it’s all true. As third world nations starve, we grow fuel!

    Ethanol is a hydrocarbon c2h5oh. Octane 104. The fuel is produced from a fermentation process from fast growing energy crops, sugar cane, wheat, maize, and sometimes bio-degradable waste animal feed and timber. The claim is that due to the renewable factor it has an advantage over fossil fuel. Vehicles can operate with up to 85% bio-content, with no operational disadvantages with high CO2 reduction. I can confirm from my European motorcycle tour this year, that e10 bio-ethanol fuel is widely available.

    Considerations
    Just before you dash out to join the Green Party, there are some technical considerations the government seems to have overlooked. Bio-ethanol fuel is corrosive, copper, aluminium, plastics and rubber list among its appetite. Just before I forget, there is a critical lubrication service update; this is due to an increase in fuel oil contamination.

    I think you’re starting to get the picture, now let’s focus on its combustion problems. It has a unique evaporation envelope around 78ºC. It also requires a significant increase in fuel quantity on cold start, often requiring a pre-heater system, and a much-modified ignition profile. However, on the positive side once efficient combustion is achieved the knock resistance affords a more aggressive ignition angle and increased cylinder pressures.

    I am going to focus on Audi who have offered a flexi fuel A4 since 2009! It could operate up e85 with no modification. To my knowledge there are no or very few bi-ethanol vehicles in the UK. You may have noticed warning stickers in the fuel filler cap on most vehicles, expressing non- bio compatibility.

    So, back to my point: Why is the uk government considering a pilot trial for e10? Currently all gasoline sold in the uk can have e5 content without any notification at the pumps.

    Requirements
    Moving on to the technical requirements, the Audi flexi-fuel engine is based on the 2.0 tfsi, with Bosch med 17.1 control. Sequential mapped ignition, with knock control, digital hot film air mass measurement. Fuelling is homogenous direct injection, with port injection on cold start. Intake cam adjustment with avs on the exhaust cam.

    Due to low vaporisation when cold, ‘autarkic cold start’ ,the air fuel mixture cannot form the required composition for ignition. Significant modification to con rods and bearings are required to withstand higher cylinder pressure. Modifications to the variable load in- tank pump components and wiring prevent corrosion damage. An additional digital fuel quality sensor is fitted to the
    low-pressure fuel line, this enables critical adjustment to thermodynamic fuel properties and ignition maps.
     
    Bosch injection control strategy includes injection on intake and compression, with multiple strike on compression when cold, with additional injection pressure of 150 bar. A new aluminium manifold with a port injector is fitted to avoid pre-heaters on cold start.
    The point I am trying to make here is not based on a simple pessimistic naivety, but a serious concern that not enough focus is being applied to a long-term strategic solution. Two key prerequisites will have to be recognised, the first is a reconstruction of social order around a coherent public transport system, and the second a recognition that private vehicle transport is a privilege and not an automatic right.


  • In the heat of the fault  

    At the workshop we cover all kinds of vehicles, old, new, big and small but with all these vehicles we need up to date diagnostic equipment to be able locate faults within the electrical system.
        
    In the workshop this summer was a 2009 Volkswagen Golf that had an intermittent issue which meant the car would go into limp mode, the cruise control was disabled and the climate control wouldn’t work. Understandably in the weather we were having the lack of air conditioning was a major concern to the customer. No one wants to be without air conditioning in 30Cº.
        
    I plugged in the trusty diagnostics reader and came up with four faults. These included turbo boost sensor, manifold pressure, throttle pedal position sensor and ‘fuel system
    too rich’.
        
    In my experience cars can throw up all kinds of trouble codes even when there is no issue with that part. I wouldn’t say some manufacturers are more troublesome than others but if a light does appear on the dash it’s best to get it checked out as soon as possible.

    Issues
    I cleared the fault codes and told the customer to see how it drove and if the issues resolved themselves. The customer had the car for just an hour before they called and said that the problem had reoccurred, as much as this is a pain for the customer I always clear the faults and see if it happens again rather than changing unnecessary sensors. I got the Golf back into the workshop and once again plugged the computer in, which brought up one code. This was the throttle position sensor. A quick call to VW and a discussion with their parts people showed that this particular issue can lead to the cruise and climate control not working.
        
    Next day delivery on the part means the car came back in the following day. One bolt, two plastic clips and an electrical connection later and the pedal was off. Gone are the days of the throttle cable. The throttle response is now done by a sensor on the pedal which works out how far the pedal is being pushed and tells the engine how to respond. It is clever stuff,  when it works.
        
    A pedal replacement on the Golf only takes five minutes and another clear of the fault code before taking the car for a road test. On the test drive cruise and climate control were checked as well as making sure no dash lights had appeared.
        
    Modern mechanics have become very computerised. Dash lights appear whether it is indicating an issue with the airbag systems, ABS or engine and diagnostic computers are so important to narrow down what the issue could be. I dislike the reliance that some workshops put on just trusting what appears on the screen of the diagnostics. It is still imperative that mechanics test sensors and look into live data to make sure that unnecessary components are not replaced and the costs put onto the customer, who will have to pay.


  • Issues of rotation 

    I received a phone call from another garage: 'We've seen you in the Top Technician magazine and are wondering if you would be interested in looking at an ABS fault for us?' The call went along the usual lines, can the symptoms be recreated? What is the repair history? The vehicle was booked in for me to take a look.

    The car in question was a 2011 Honda
    CR-V, which had been taken as a trade in at a local garage, the fault only occurred after around 50-70 miles of driving, at which point the dash lights up with various warning lights. The vehicle had been prepped and sold to its new owner unaware a fault was present.

    Fault-finding
    After only a few days the fault occurred and the vehicle returned to the garage. They had scan checked the vehicle and the fault code ‘14-1- Left Front Wheel Speed Sensor Failure’ was retrieved. On their visual inspection, it was obvious a new ABS sensor had already been fitted to the N/S/F and clearly not fixed the fault. Was this the reason the vehicle had been traded in? They fitted another ABS sensor to the N/S/F and an extended road test was carried out. The fault reoccurred. This is when I received the phone call; the garage was now suspecting a control unit fault.
        
    My first job was to carry out a visual inspection for anything that was obviously wrong and had possibly been over looked: correct tyre sizes, tyre pressures, tyre tread and excessive wheel bearing play. All appeared ok. The ABS sensors fitted to this vehicle are termed 'Active' meaning they have integrated electronic and are supplied with a voltage from the ABS control unit to operate. The pulse wheel is integrated into the wheel bearing, which on this vehicle makes it not possible to carry out a visual inspection without stripping the hub.

    Endurance testing
    With the vehicle scan checked, all codes recorded and cleared, it was time for the road test. Viewing the live data from all the sensors, they were showing the correct wheel speed readings with no error visible on the N/S/F. The road test was always going to be a long one, fortunately at around 30 miles, the dash lit up with the ABS light and lights for other associated systems; the fault had occurred. On returning to the workshop, the vehicle was rescanned, fault code '14-4 - Left Front Wheel Speed Sensor Failure’ was again present. Again using the live data the sensor was still showing the wheel speed the same as the other three, so whatever was causing the fault was either occurring intermittently or there was not enough detail in the scan tool live data graph display to see the fault. It was time to test the wiring and the sensor output signal for any clues.
        
    Using the oscilloscope, the voltage supply and the ground wire were tested and were good at the time of test. I connected the test lead to the power supply wire and using the AC voltage set to 1V revealed the sensors square wave signal. Then rotating the wheel by hand and comparing the sensors output to one of the other ABS Sensors, again all appeared to be fine. A closer look at the signal was required, zooming in on the signal capture to reveal more detail; it became easier to see something was not quite right with the signal generated by the sensor when the wheel was rotated. With the voltage of the signal remaining constant, a good earth wire and the wheel rotated at a constant speed the signal width became smaller, effectively reporting a faster speed at that instant, not consistent with the actual rotational speed of the wheel. It was difficult to see the error, zooming out of the capture to show more time across the screen it could be seen that this appeared in the signal at regular intervals, although not visible all the time because it was such a slight difference. Using the cursors to measure between the irregular output and counting the oscillations, it was clear that it occurred at exactly the same interval every time. It had to be a physical fault on the pulse wheel.
        
    This meant a new wheel bearing was required. The vehicle was returned to the garage as they wanted to complete the repair, a new wheel bearing was fitted and extended road testing confirmed the vehicle was now fixed.

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