Call our Sales Team on 0208 912 2120

Electronics on the move

26th November 1987, Page 124
26th November 1987
Page 124
Page 125
Page 126
Page 124, 26th November 1987 — Electronics on the move
Noticed an error?
If you've noticed an error in this article please click here to report it so we can fix it.

Which of the following most accurately describes the problem?

We look at the Diesel Diagnostic Service available to Mobil's major customers and at some of the equipment on the market for getting our own show on the road

• The benefits, of electronic diagnostic equipment have now become so great that an operator can make real savings by keeping an electronic eye on his vehicles. Unfortunately the cost of a full range of diagnostic equipment is prohibitive to all but the largest operators.

One company that is helping to fill that gap is Mobil, which operates a diesel diagnostic service that is free to its major customers. By travelling from one workshop to another, Mobil can justify the 2150,000 investment which can supply information to build up a comprehensive picture of an engine's performance.

To see how the picture is built up, we accompanied Mike Frost, one of the four Mobil diesel diagnostic operators on a visit to the BBC Transport Department at Acton. A varied fleet of vehicles operate from this depot, and although they do not cover a huge distance, they can spend a long time idling, which can provoke unusual problems.

Operator is Mal

Despite the impressive array of electronic wizardry, the crucial asset in the Mobil armoury is the operator, in this case Mike Frost. Having spent a long time working on engine test beds, he is well qualified to get a realistic interpretation out of his equipment. As he measures a series of the engines functions, he is able to build up a comprehensive picture.

The vehicle that came under scrutiny is a Ford Cargo 2517 tractive unit powered by a Perkins V8 540. The first test is for engine performance, using the Syntec power and torque test. This is sometimes wrongly described as a rolling road in a box, but it does not measure absolute power, rather the state of acceleration of the engine. This is measured with a sticker applied to the flywheel: optics and electronics translating the result.

As the weight of the flywheel is known, it gives a clue to the power output, but most important, a series of tests gives a good overall picture of how consistently an engine is performing. That is the real strength of all the tests, the picture that they give an operator of how his fleet is wearing. An annual summary of all the tests is supplied by Mobil.

The Syntec, which is Swiss built, gives its results both numerically, and as a graph. By using the graph paper from an earlier test, an exact comparison can be made of an engine's performance over a period of time.

Timing error common

The most common fault found is an error in the injector timing. Two or three years ago, Frost was finding that some of the worst timing errors were to be found on new engines, but recently new engines have improved greatly, and the greatest number of errors are found in engines that are settling down. One manufacturer that employs a right-angle drive to the injector pump, has taken steps to eliminate a steady rate of wear in the drive gears, which meant that the injectors tended to run permanently retarded.

As a rule of thumb, every degree of error in the injector setting results in one per cent more fuel being burnt. To check the accuracy of the timing, Mobil uses an AVL timing device, that senses the pressure waves inside the injector pipes, and so fires a strobe light. This is adjusted so that when the top dead-centre mark on the flywheel aligns with the static register point, the amount of advance is read off the control box.

The sensors, or transducers, are clipped to the injector pipe close to the pump, once the paint has been removed. Being a dynamic test it is inevitably more accurate than a static test, as wear in the pump drive is automatically accounted for. The engine is tested at the lowest speed that it will run at, without hunting.

Although Frost has the ability to adjust any error he finds in the timing, because his job is to test rather than fix, when he finds an en-or, he tells the fitter, who does the adjustment, Unfortunately Frost has often left by by the time the job is done, so cannot do a retest to verify the accuracy of the adjustment.

Another test that is relative rather than absolute is the compression test. Rather than measuring the actual compression of each cylinder, this test leaves the injectors undisturbed and uses electronics. By measuring the voltage drops over the battery terminals while the engine is being cranked over, and recording them as a graph, the effort required to compress each cylinder compared to its neighbours can be seen easily.

Art of interpretation

The clever part of this test comes not from the machine, but from the operator. Frost has been doing this test for long enough to be able to say from the shape of the curve what the cause of any compression loss is likely to be. In this particular case, he checked that the pattern repeated itself over eight cycles (the engine having the eight cylinders). The shape of the peaks of the curve indicated that the tappets needed adjusting. As the injector pipes are routed over the top of the rocker covers, this was bad news for the fitter, but may have prevented a valve being burnt out at a later date.

Before this test could be satisfactorily done, the fuel cut-off had to be wired out of the way, as even in the off position, it still let enough fuel through to allow the engine to fire lightly, so affecting the reading. Once again the operator's practical background proved vital. Recognition of starter motor wear, or wear in the pinion or ring gear is obviously essential, but should a serious compression loss be detected, there is a further weapon in the Mobil armoury. A borescope is another piece of equipment that an operator might find very useful, but occasionally costs too much for something that will only be used very occasionally. One is carried on the Mobil van, and although not often used, allows the inside of the combustion chamber to he inspected and even photographed.

A smoke test completes the jobs that are done on the actual vehicle. This test measures the blackness of the smoke rather than the chemical content of the emissions, and completes the picture given by the compression test and the timing test, so giving a good impression of the actual combustion conditions.

The smoke output varies hugely depending on the conditions that the engine is running under. Frost waits until the engine is warm, although it will never reach full operating temperature in neutral. He then measures the "initial high", which is the smoke given off in initial acceleration, and "steady state", which is the engine running at a constant high speed.

Final test: oil analysis

The final test for the vehicle is an oil analysis. A sample is lifted out of the sump, nixed with an anti-coagulant solvent, and separated out in a centrfuge carried in the back of the van. If the oil contains more than 3% of insolubles, then the oil must be changed. A viscometer test completes the oil analysis, but if there are signs of any metal deposits in the oil, it is sent to the Mobil laboratories to be analysed.

The Mobil Diesel Diagnostic Service is not restricted to the road haulage industry. Frost increasingly finds himself monitoring the performance of marine engines and heavy industrial power plants. It is, however, restricted to major customers of Mobil oil. There is no strict cut-off point and every case is treated on its merits.

Marketing is the obvious justification for Mobil running this free service, but Frost thinks that it could provide real benefits and savings to the smaller operator, or owner-driver. He feels that there is a market for such an operation, but run as a profit-making centre in its own right. The worth of the service is not only proved financially, but also by the BBC fitter vto was waiting for the Mobil diagnoses before he started working on a particularly troublesome vehide.

For the operator who wants to establish his own diagnostic service, Souriau in conjunction with Perkins, has developed an electronic diagnostic system called the Perkins Powertune. Able to test either diesel or petrol engines, from two to 12 cylinders, it displays its findings on a

screen, as well as providing a printout.

Like the system operated by Mobil, the Powertune 2611P uses a clamp-on sensor to measure the pulse in the injector pipe feeding number one cylinder. When the lines marking top-dead centre are aligned under the strobe light, both screen and printout will give the number of degrees advance. There is also a clamp-on sensor for the ignition leads of a petrol engine.

The rest of the Powertune test uses information gleaned from the battery terminals. A pair of robust crocodile clips on the terminals measure the voltage drop as the engine is turned over, so measuring the relative compression in the cylinders.

Menu driven system

If a cylinder is more than 15% down on any of its neighbours, the "menu" on the screen will recommend further investigation, and the Powertune will then analyse the compression loss further. The results are recorded digitally rather than graphically, the Perkins claims that this is unambiguous, unlike "wavy lines on screens", and that the "menu driven system" does not require vast amounts of expertise to operate. A day's free training comes with every Powertune 2611 purchased.

The Powertune tests do not stop at the engine. The crocodile clips measure the voltage across the battery, and a further probe, which uses the hall affect, measures the current or ampage passing down the battery lead. Between the two is derived the wattage, or power.

By running the engine up to between 1,000 and 1,500rpm, the performance of the voltage regulator and cut-out is measured, and then the alternator is put under load by turning on all the electrical systems. The performance of the entire charging system is then checked, including the rectifier, which converts the alternating current from the alternator into direct current.

The Powertune is available as either the 2611, or the 2611P, the P standing for portable. The only difference between the two is that the portable version is mounted onto a smaller frame for fitting into a vehicle. They both cost 26,890, and to enable the portable version to be run from the vehicle battery; an inverter is available for a further 250. The inverter also doubles as a battery charger.

The Powertune has been designed with the future in mind, as modules can be added to the existing package, to cater for advances such as electronic fuel injection, which engineers at Perkins feel sure is just around the corner.

There is a further device in the Powertune range, and that is the 1591. This is universal timing unit, which can be used for either diesel or petrol engines, runs off the battery of the vehicle being tested, and costs £1,450.

Bernard Miles, a control systems analyst at Perkins, says that electronic diagnosis of diesel engines is now suffering from the same attitudes that greeted the use of electronics to diagnose faults in petrol engines ten years ago. He believes that once the benefits of electronic diagnosis have been demonstrated, and operators have started to reap the increased profits from a carefully monitored vehicle, its adoption will become universal.

Having invested in an expensive set of electronics to equip a mobile diagnostic centre, there is a further problem: how to stop all your valuable kit bouncing around in the back of the van. Mobil has solved the problem in a thoroughly four-star fashion, with fittings that befit an operation that is essentially a marketing exercise. As it's a purely diagnostic service, there is no need to carry tools.

The Swedish concern Edstrom has recently expanded its range of vehicle racking available in the UK. The strength of the system is that it is made up from a series of interlocking modules, comprising the shelves, drawers, working tops, and so on. Because each of these modules is inherently very strong, there is no framework as such, and the interlocking modules are easily taken apart and reassembled, or added to should the need arise. Edstrom claims that a set of interior fittings will last up to three times the life of the vehicle that is carrying them.

A further device to enable work to be done on site, is an aluminium deck that slides out from the floor of a van. Legs take the weight of the platform, which can carry up to 400kg, therefore making a much more solid workbench than one mounted solely on the van: the Qualdeck comes from Quality Industries.

As a commercial vehicle powerplants ' become increasingly finely tuned, servicing is inevitably going to become more and more specialised and the type of service being pioneered by the Mobile Diesel Diagnostic Service, will become more popular. The cost of much of the equipment means that for the smaller operator to have access to electronic diagnosis, it will have to be a mobile serVice. It is a market that is waiting to be exploited.



People: Bernard Miles

comments powered by Disqus